The Iberian Rivers

Chapter 4

The Iberian Rivers Sergi Sabater

Maria Jo~ao Feio

Manuel A.S. Gra¸ca

Institute of Aquatic Ecology, University of Girona, Campus Montilivi 17071, Girona, Spain Catalan Institute for Water Research (ICRA), Girona, Spain

IMAR and Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal

IMAR and Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal

Isabel Mun˜oz

Anna M. Romanı

Department of Ecology, Faculty of Biology, University of Barcelona, Avenue Diagonal 645, 08028 Barcelona, Spain

Institute of Aquatic Ecology, University of Girona, Campus Montilivi 17071, Girona, Spain

4.1. 4.2.

4.3.

4.4.

4.5.

Introduction The Guadiana 4.2.1. Historic Changes and Human Impacts 4.2.2. Biogeographic Setting 4.2.3. Physiography, Climate, and Land Use 4.2.4. Geomorphology, Hydrology, and Biogeochemistry 4.2.5. Aquatic and Riparian Biodiversity 4.2.6. Management and Conservation The Guadalquivir 4.3.1. Historic Changes 4.3.2. Biogeographic Setting 4.3.3. Physiography, Climate, and Land Use 4.3.4. Geomorphology, Hydrology, and Biogeochemistry 4.3.5. Aquatic and Riparian Biodiversity 4.3.6. Management The Duero 4.4.1. Historic Changes and Human Impacts 4.4.2. Biogeographic Setting 4.4.3. Physiography, Climate, and Land Use 4.4.4. Geomorphology, Hydrology, and Biogeochemistry 4.4.5. Aquatic and Riparian Biodiversity 4.4.6. Management and Conservation The Ebro 4.5.1. Historical Perspective 4.5.2. Biogeographic Setting 4.5.3. Physiography, Climate, and Land Use 4.5.4. Geomorphology, Hydrology, and Biogeochemistry

Rivers of Europe Copyright Ó 2009 by Academic Press. Inc. All rights of reproduction in any form reserved.

4.6.

4.7.

4.5.5. Aquatic and Riparian Biodiversity 4.5.6. Management and Conservation The Tagus 4.6.1. Historical Perspective 4.6.2. Biogeographical Setting 4.6.3. Physiography, Climate, and Land Use 4.6.4. Geomorphology, Hydrology, and Biochemistry 4.6.5. Aquatic and Riparian Biodiversity 4.6.6. Management and Conservation Additional Rivers 4.7.1. The Ag€ uera 4.7.2. The J ucar 4.7.3. The Mondego 4.7.4. The Segura 4.7.5. The Ter 4.7.6. Conclusions and Perspectives Acknowledgements References

4.1. INTRODUCTION The Iberian Peninsula encompasses a variety of climatic influences within a relatively small geographical space. There is a 4  C difference between the annual average temperature in the septentrional and the meridional coasts of the Iberian Peninsula. The complex orography causes large variations in climate at local and regional scales. For example, summer temperatures in the Guadalquivir river basin may reach 47  C, while winter temperatures may reach 20  C in the 113

114

PART | I Rivers of Europe

at >30%. Rainfall can be intense in the Mediterranean area (50 mm in 1 h), in particular at the end of summer and autumn that causes Horton runoff. Rainfalls of 400–600 mm in a single episode are common in the Mediterranean and, at times, in the Atlanticarea (Martın-Vide & Olcina 2001). However, extended dry periods up to 160 days are also common in some areas. Consequently, runoff coefficients range from 16% in some Mediterranean areas to >50% in the Atlantic region. Rivers of the Iberian Peninsula can be separated by those flowing to the Atlantic and those flowing to the Mediterranean. The separation between these two large basins is asymmetrical with the Mediterranean basin encompassing 182 661 km2 (31% of the total surface area) and the Atlantic 400 839 km2 (69% of the surface area) (Teran & Sole Sabarıs 1978). The largest rivers flow to the Atlantic and include the Duero, Tagus, Guadiana, and Guadalquivir. The Ebro is the only large river in the Iberian Peninsula that flows into the Mediterranean (Figure 4.1, Table 4.1).

Central Plateau (Mesetas). There is also large spatial variation in rainfall, which decreases from north to south and from west to east. Therefore, the Iberian Peninsula can be divided into arid, humid, and semi-desert areas. The division between the humid and arid areas is established at the precipitation isoline between 600 and 800 mm/year, while that between the arid and semi-desert area is 300–350 mm/year (Martın-Vide & Olcina 2001). The humid area (1000–2000 mm/year) not only occupies the north, but also includes many mountain ranges within the Iberian Peninsula. The arid area is the largest, as it includes the Meseta, Ebro and Guadalquivir depressions as well as the Mediterranean littoral area. The semi-desert zone is small and constrained to the southeast. Interannual variability in rainfall is high, being most pronounced in the arid and semi-desert areas. This variability is >20% inthe Mediterranean front and upto40% in the southeast of the Peninsula (Martın-Vide & Olcina 2001). Those basins showingthe highest variability are the Seguraand Guadalquivir TABLE 4.1 General characterization of the Iberian Rivers

Mean catchment elevation (m) Catchment area (km2) Mean annual discharge (km3) Mean annual precipitation (cm) Mean air temperature (C) Number of ecological regions Dominant (25%) ecological regions Land use (% of catchment) Urban Arable Pasture Forest Natural grassland Sparce vegetation Wetland Freshwater bodies Protected area (% of catchment) Water stress (1–3) 1995 2070

Ter

Ebro

J ucar

659

770

817

Segura Guadalquivir Guadiana Tagus 644

566

3010 85362 21208 19182 57527 0.83 13.41 0.81 0.82 7.22

504

599

Mondego Duero

Ag€ uera

391

358

874

67048 80600 6670 6.18 9.93 3.10

97290 13.56

145 0.10

78.6

67.2

44.8

39.8

52.1

53.2

59.9

93.7

66.5

106.0

11.7 2

11.4 6

13.1 3

14.4 3

15.5 3

15.2 4

13.8 4

14.4 3

11.4 4

11.7 1

48

37

37

37

37; 66

37

37

12; 50; 66

37; 50

12

2.6 30.0 1.1 50.3 14.3 1.1 0.0 0.6

0.6 47.1 1.9 22.3 25.5 2.7 0.1 0.6

0.7 51.6 0.0 17.2 29.8 0.3 0.0 0.4

1.7 53.4 0.0 14.6 24.9 4.9 0.2 0.3

1.1 62.0 0.0 12.8 20.9 1.6 0.8 0.8

0.6 68.4 0.1 7.8 21.8 0.2 0.2 0.9

1.7 45.6 0.3 21.5 28.8 0.8 0.0 1.0

1.9 33.4 0.1 38.2 23.9 1.8 0.2 0.5

0.7 55.1 1.0 17.5 23.5 1.8 0.0 0.4

0.2 7.3 14.6 48.8 24.4 4.7 0.0 0.0

2.0

3.2

0.1

4.9

15.8

3.5

2.2

10.8

1.2

0.0

1.7 2.3

2.9 2.9

3.0 3.0

3.0 3.0

3.0 3.0

2.9 2.9

2.9 3.0

1.5 1.6

2.0 2.9

2.0 2.0

Fragmentation (1–3) 3 Number of large dams (>15 m) 3 Native fish species 6 Nonnative fish species 9 Large cities (>100 000) 0 108 Human population density (people/km2) Annual gross domestic 20 387 product ($ per person)

3 70 27 20 5 34

3 13 19 11 1 207

3 15 3 4 1 78

3 55 22 7 3 69

3 87 29 13 0 24

3 72 23 10 2 136

3 3 12 7 0 96

3 75 21 13 5 37

2 0 4 ? 0 36

19 587

14 873

13 782

12 994

12 303

13 818

8550

15 058

19 055

For data sources and detailed explanation see Chapter 1.

Chapter | 4 The Iberian Rivers

FIGURE 4.1 Digital elevation model (upper panel) and drainage network (lower panel) of the Iberian Rivers.

115

116

This apparent asymmetry is caused by the structure and geology of the Iberian Peninsula. The central plateau (Meseta) is tilted to the west and the Iberian Range delimits its east border. As a consequence, waters flowing to the Atlantic follow the tilted plain of the Meseta: Duero to the north, Tagus and Guadiana to the south. The orography of the Meseta determines the length and fluvial character of the rivers, with the Atlantic rivers being longer and lower gradient than the Mediterranean rivers. These rivers tend to be torrential and irregular, producing devastating floods in autumn and droughts in summer. Rivers flowing from the Cantabric Range are quite short, but transport large amounts of water because of high rainfall. Water from the Pyrenees feeds the large river Ebro, while those of the Bethic Mountains feed the Guadalquivir. The variation in orography and climate also influences the different flow regimes of Iberian rivers. Rivers of the Pyrenees have a nival regime with a maximum in spring and a relatively constant flow in summer. Mediterranean rivers have a rainfall-based flow regime with maxima in spring and autumn and a minimum in summer. Rainfall-fed Atlantic rivers have much higher inputs with a slight decrease in summer flow. Because of the length and complexity of the landscape, flow regimes of some rivers also can vary. For example, headwaters of the Ebro are in the karstic area of Fontibre with an Atlantic influence. Downstream in the Ebro Depression, the flow regime progressively shifts to a Mediterranean type. The lower Ebro has a pluvio-nival flow regime after rivers from the Pyrenees enter the system. The geology of the Iberian Peninsula is complex and affects the biogeochemistry of its waters. In general, the west is siliceous and the east is sedimentary and calcareous. Armengol et al. (1991a) characterized four types of waters based on total dissolved solids (TDS) and ionic composition. Western water bodies draining igneous geology have low TDS and high levels of sodium and potassium relative to calcium and magnesium. Eastern waters, for example systems in the Ebro and Duero catchments, have moderate TDS and are high in bicarbonates. A small group of waters in the southeast in the J ucar and Segura basins are high in sulphates and TDS. Finally, a small number of waters in the southwest have the highest TDS values and high chloride concentrations. Human influence on water ecosystems has a long history in the Iberian Peninsula; for example there are remnants of hydraulic structures built by the Romans and the Arabs. In recent times, water scarcity in systems with irregular flow regimes has resulted in the construction of dams and canals, resulting in the regulation of many Iberian rivers. Over 1000 reservoirs have been built along most of the large rivers. Large rivers in the northwest, however, are less regulated. Some rivers have been interconnected, allowing interbasin transfer of biota and endangerment of sensitive species. Many rivers, especially those in the arid region, are dependent on groundwater. This has particular relevance in future climate scenarios that predict base flows to decrease and the number of temporary systems to increase (Alvarez Cobelas et al. 2005).

PART | I Rivers of Europe

4.2. THE GUADIANA The Guadiana derives its name from the Roman Anas or Ana with the addition of the prefix Guadı (river) by the Arabs. Although the Guadiana is the smallest of the large rivers in the Iberian Peninsula, it is remarkable for the nature of its drainage network and flow regime. Because of the porosity of its substrate and a moderate rainfall in the catchment, groundwater plays an important role in river flow. The catchment also has high human impacts that influence its flow regime, water chemistry, riparian vegetation, and biological communities (Photo 4.3). The Guadiana catchment is wide and flat, and its flow is derived only from rainfall. Most of its headwaters are in the Meseta and are of low gradient. The Guadiana catchment covers 67 048 km2 and most lies in the driest area of the Meseta. Because of the high permeability of the limestone bedrock, rainwaters disappear quickly from the surface and form large underground aquifers. The river has a highly variable flow regime. Where the chalk and limestone are interrupted by an impervious layer, springs originate and are characteristic of the Guadiana hydrography. The river is unconstrained for most of its 818 km, being constrained partly in the Campos de Calatrava and later when entering Portugal. The river drops by only 1 km from the headwaters to the mouth. The Guadiana originates from a diffuse number of tributaries, and thus the primary source is still under discussion. The main headwater tributaries include the Zancara, Gig€uela (or Cig€uela), Jabalon and Zujar. The lower tributaries, Bullaque and Estena, drain the Toledo mountain range and originate in Cabaneros National Park. They are some of the best conserved in the entire Guadiana basin. The Gig€ uela contributes the most flow in the upper Guadiana, while the Zujar has the highest flow in the catchment. The lower Guadiana has a number of short streams with highly unpredictable flows. Particularly important is the Vasc~ao because of its good condition in an area where most flowing waters have been seriously altered by humans. Human impacts in the catchment are mostly related to agricultural practices that use a large number of wells and reservoirs. The Guadiana catchment holds the largest man-made lake in Europe, the Alqueva reservoir in Portugal, with water storage of 4.15 km3. The catchment has a high water deficit, indicating a scarcity of water for aquatic biota.

4.2.1. Historic Changes and Human Impacts By the end of bronze era, the southwest Iberian Penınsula had its own identity with several fortified villages along the lower Guadiana. Here, the Tartessos kingdom was the first political entity of Iberia. This area was later occupied by Phoenicians (7th century BC), Greeks (6th BC) and then by Carthaginians and Romans because of its high metal abundance. For example, San Domingos mine has been in use intermittently for >2000 years. Mertola, several km upstream of the Guadiana

117

Chapter | 4 The Iberian Rivers

PHOTO 4.1 Guadiana at Pulo-do-Lobo (Photo: Manuel Gra¸ca).

mouth, was an important port during the Arabic period with evidence of Greek and Jewish merchants and Berber warriors. Badajoz, with 3000–5000 habitants, was an important Arab city in the 10th–11th century, replacing Merida as one of the most important cities in the south.

4.2.2. Biogeographic Setting The Guadiana mostly flows through the Meseta highlands (600 m asl on average), an area of primary materials partly covered by tertiary sediments (Teran & Sole Sabarıs 1978). The southern Meseta geology consists of: (1) the original primary materials in the west, (2) the Toledo Mountains in the north, (3) an interior depression, later filled by Tertiary deposits, limestones and gypsum, and (4) the northeast Iberian Range made up of Mesozoic materials.

The Meseta was formed by Alpine foldings that created mountain ranges on each side and caused its western tilt. During this Alpine forcing, Tertiary depressions were separated from the sea and erosion of the surrounding ranges contributed sediment materials to the depression. Most of this process was completed during the Miocene. The sediment layer is 300 m on average; the lower layers are sands and silts and the upper layers are gypsum and limestones. Finer materials were deposited in the centre of the depression, whereas more gypsum, limestones, and halites are found in the east.

4.2.3. Physiography, Climate, and Land Use Schists, gneisses and granites constitute the Paleozoic bedrock of the upper Guadiana basin. There are a series of

118

Triassic, Jurassic, Cretaceous and Tertiary detrital and carbonate materials covering the bedrock. In Portugal, deposits of alkaline meta-sedimentary and meta-volcanic sediments occur along with acidic areas of Cenozoic sediments. Climate in most of the Guadiana basin is Continental Mediterranean with cold winters, low rainfall, and long dry summers. Low winter temperatures may last for nearly two months, an unusual phenomenon for a Mediterranean climate. Summer temperatures are high but humidity is low. The annual range in air temperature can be nearly 50  C, and diel temperature variation in summer can be 20  C. Mean annual rainfall is 400 mm, mostly occurring during winter and spring. The catchment is mostly dedicated to agriculture, which is highly dependent on irrigation. In 2002, there were >350 000 ha irrigated in the catchment with 57% relying on phreatic waters. Irrigation has decreased the phreatic level in recent times, surpassing the renewal capacity of these waters by 300 Hm3 per year. There are over 60 847 wells being used in the catchment. Most of the catchment in Portugal is covered by cork-oak forest and Mediterranean shrubland, and has a low human density (230 000 inhabitants; 20 inhabitants/km2). Industry is scarce with some olive processing plants and pig farms.

4.2.4. Geomorphology, Hydrology, and Biogeochemistry The total drainage network of the Guadiana equals 33 707 km with an annual discharge of 6168 Mm3. Regardless, many sections of the river, the upper catchment in particular, are intermittent, especially in summer. Rivers in the upper catchment are closely interconnected with underground aquifers. The combination of low rainfall and high evaporation causes flows to be typically low. In fact, most waters in the upper catchment infiltrate as groundwater and form four large aquifers (Fornes et al. 2000). The largest (5500 km2 surface area) is the West Mancha aquifer (Number 23). Formerly, the outflow from this aquifer was the ‘Ojos del Guadiana’ (Guadiana’s Eyes) in the La Mancha plain (608 m asl). Here a number of diffuse springs emerged that were considered the ‘real’ Guadiana headwaters, but which vanished >30 years ago. Today, surface waters of the Guadiana originate from karst formations in the Montiel range. These waters form the Ruidera lakes (15 in total) and have a high carbonate load. Water levels in the lakes are associated with rainfall in the upper mountains, having a delay time of 4–6 months. These small lakes are interconnected by a series of small waterfalls and by subsurface flow. The first lake in the series is La Blanca (White Lake after the white-coloured carbonate precipitates). Colgada is the largest lake (100 ha surface area), while the others range from 12 to 38 ha. Water depths in the lakes range from 8 to 19 m. The lower lakes become progressively shallower and are covered by emergent macrophytes. The Penarroya reservoir collects

PART | I Rivers of Europe

the waters from Ruidera, but water infiltrates and the river disappears for the first time. Fifty kilometres downstream are found the Tablas de Daimiel, a group of large shallow ponds and swamps that is susceptible to flooding because of the low gradient. This wetland covers an area of 1712 ha, is rectangular in shape, and consists of small lacustrine openings with islands and palustrian vegetation of fens, reeds and rushes. Although originally fed by the Gig€uela and aquifer 23, the wetland now obtains water from other watersheds because of aquifer depletion. From the Tablas, the Guadiana flows west and then south through La Mancha plains, penetrating the Toledo range. Downstream, the Guadiana is dammed, forming Cıjara reservoir. It is the first of three reservoirs (Cıjara, Garcıa de Sola and Orellana) that are later joined by Zujar reservoir on the tributary Zujar. Further downstream, the Guadiana enters the Alto Alentejo in Portugal with a hercinic substrate partially covered by quarternary and tertiary deposits. The river alternates between waterfalls (e.g. the 16 m high Pulo do Lobo waterfall) and unconstrained reaches with slopes <5%. The Guadiana at Merida has an average discharge of 157.4 m3/s, but ranges between 2.2 and 463 m3/s. The Guadiana mouth forms a small delta in the estuary, where small islands alternate with sandbars. Because of the low elevation, tidewaters can reach Mertola about 70 km upstream from the mouth. Brackish waters dominate only from Alcoutim to the mouth, and there are several marshes. Tributaries are commonly dry during summer and some even in winter. The Gig€uela at Tablas de Daimiel has an average discharge of 57.1 Mm3/year (1995–2001), with maxima in February and minima in winter and summer (CH Guadiana 2002). The Zancara has a maximum flow of 2.4 m3/s, whereas the Zujar is regulated and discharge ranges between 2.9 and 66.5 m3/s. Water transparency is high in the Guadiana headwaters, in particular in the upper ponds of Ruidera. Suspended solids in this area reach 4.8 mg/L, but quickly increase downstream because of inputs of sediments, treated wastewaters, and agricultural and urban runoff. Reservoirs reduce suspended solids in the river. Pools are frequent along the river and often have dense phytoplankton communities, including cyanobacteria, which increase water turbidity. At the mouth, the concentration of suspended solids is 38 mg/L, but can reach 84.6 mg/L at Sanlucar de Guadiana. Water conductivity is high (1000 mS/cm) in the headwaters as well as in Zancara and Zujar because of the calcareous substrate. Conductivity of the Gig€uela and the Tablas is also high (1400–2400 mS/cm, locally reaching 8000 mS/cm). In the Zancara and Gig€uela, conductivity can reach 3000 mS/ cm. Water conductivity decreases downstream because of inputs from poorly mineralised springs and chemical changes in the reservoirs (CH Guadiana 2002). Conductivity values of 490–550 mS/cm have been recorded in the Alqueva reservoir, and the tributaries Xevora, Vasc~ao, Ardila and Degebe in Portugal have conductivities of 350–400 mS/cm.

Chapter | 4 The Iberian Rivers

Pollution, indicated by high ammonia levels, is occasionally detected below wastewater treatment plants and from direct inputs of wastewater. Dissolved phosphorus is high in some areas downstream of large cities. Nitrate is higher in winter as a result of increased runoff; whereas ammonia and phosphate have higher values during summer during low flows. Organic and inorganic contaminants are rarely recorded in the Guadiana (CH Guadiana 2002), their occurrence being related to the agricultural land use. Tributaries flowing through villages, farms and agricultural lands in the lower Guadiana (i.e. Olivenza, Ardila and Asseca) receive high pollution loads. In summer, the combination of low flow, high temperature and high nutrients, particularly phosphates, results in periodic blooms of Cyanobacteria or Azolla. Cyanobacteria blooms usually occur in the estuary at the end of summer, and the sediment load into the estuary ranges between 58 and104 m3/year.

4.2.5. Aquatic and Riparian Biodiversity Planktonic development in the Guadiana mostly occurs during low-flow periods in the main channel as well as in several reservoirs in the basin. Blooms of the Cyanobacteria Microcystis aeruginosa, Aphanizomenon flos-aquae, Oscillatoria spp. and Anabaena spp. have been recorded during summer and early autumn in the river. Recent construction of the Alqueva dam has modified the hydrology of this river reach, causing more Cyanobacteria blooms (Sobrino et al. 2005). Before construction (1996–1998), phytoplankton in the river was dominated by chlorophytes (e.g. Pediastrum spp.), diatoms (Aulacoseira granulata, Melosira spp.) and cyanobacteria (Chroococcus spp. and Microcystis spp.). The lacustrine environment of Tablas de Daimiel and Ruidera lakes causes a well-developed planktonic community. In Ruidera lakes, the most common taxa were Cyclotella ocellata, C. kuetzingiana, Rhodomonas minuta, Cryptomonas erosa and Peridinium umbonatum (Bort et al. 2005). Planktonic chlorophyll-a concentrations ranged from 1 to 8 mg/L in the lakes. In the Tablas, massive growths of the cyanobacterium Planktothrix agardhii occur in summer, the diatom Cyclotella meneghiniana in spring, and the chrysophycea Ochromonas in winter (Lionard et al. 2005). Benthic diatoms are distributed according to the physiography and water chemistry of the Guadiana (Urrea & Sabater 2008). In calcareous tributaries, the diatom community is dominated by Cymbella taxa (C. affinis, C. microcephala, C. cymbiformis, C. minuta). In tributaries with siliceous substrata, the diatom community is dominated by Tabellaria flocculosa and Anomoeoneis vitrea. In eutrophic waters, the diatoms Navicula atomus var. permitis, Nitzschia acicularis, N. capitellata and N. umbonata dominate. Aquatic vegetation (submergent and emergent) is highly abundant in several areas, and especially in Ruidera and Tablas. In the upper Ruidera lakes with transparent, good quality waters, occurs an abundance of submergent vegeta-

119

tion. In the lower lakes, the water is less transparent because of sediment inputs and mostly emergent macrophytes are found. In Tablas de Daimiel, shallow and littoral areas are inhabited by several charophytes as well as other macrophytes. Cladium mariscus has an extensive development in the Tablas, probably more than in all of Occidental Europe. Riparian forests in saline soils of the Tablas are dominated by Tamarix canariensis, while Populus alba develops in less saline areas. In the river where water flow is low, helophytes such as Phragmites sp., Typha sp. and Arundo donax are common. In the estuarine zone, aquatic vegetation is mostly dominated by the invasive Arundo donax. Nerium oleander is a characteristic plant in extreme dry channels with stone substrate that are subject to floods. In headwaters of the Gig€uela, there are a few populations of the native crayfish Austropotamobius pallipes. Plecoptera, Ephemeroptera and Trichoptera, which are normally associated with running waters, are relatively less abundant in the Guadiana than in the other large Iberian Rivers. Even so, four groups of Ephemeroptera are locally abundant in the Guadiana and its tributaries (Baetis sp., Cloeon sp., Choroterpes sp., and Caenis sp.) along with Chironomidae, Simulidae and Hydropsyche sp., and the shrimp Athyaephyra desmarestii all feeding on fine particulate organic matter. The fish fauna in the lower basin is dominated by Leuciscus alburnoides and Barbus steindachneri. Some 85 km upstream from the mouth, there is a natural barrier that impedes fish migration, apart from eels (Anguilla anguilla), except during high flows. In this section, three other migratory fish also are found: Alosa alosa, A. fallax and Petromyzon marinus. The sturgeon Acipenser sturio was once present in the Guadiana, but the last specimen was caught in the early 1980s and it is now considered extinct. The Guadiana River holds the largest number of Iberian endemic fish in the Iberian Peninsula (13 out of 42 species, including introduced fishes). Some areas of the Guadiana, in particular the Tablas and streams of Cabaneros National Park, have a high diversity of fishes. The endemic Jarabugo, Anaecypris hispanica, is a small ciprinid (<6 cm in length) restricted to the Guadiana and Guadalquivir. Its habitat is limited to small slow streams with abundant submerged vegetation. Other notable endemics in the Guadiana include the Iberian barbel Barbus comiza (also present in the Tagus), Barbus microcephalus, the Pyrenean chub Leuciscus pyrenaicus, and the Iberian nase Rutilus lemmingii. Tropidophoxinellus alburnoides (Calandino), found in the Bullaque and Estena rivers in Cabaneros, is a hybrid between L. pyrenaicus and another extinct species. In fact, all T. alburnoides are females and they require the sperm of the Pyrenean chub to reproduce. Other endemics found in the upper and middle Guadiana include Chondrostoma lemmingii, Squalius alburnoides, Squalius pyrenaicus, and Cobitis paludica. A total of 15 species of reptiles and amphibians have been described from the lower Guadiana catchment. The most remarkable species are the water lizard, Lacerta scheibreri, water snakes (Natrix natrix and N. maura) and the

120

tortoise Emys orbicularis, which have some of the largest populations in the western Iberian Peninsula. The Guadiana hosts a large number of palustrian birds, especially in the less-disturbed lakes of the Ruidera and Tablas, and also in the middle Guadiana and the estuary. The Tablas is an important nesting area for the red-crested pochard. The otter is now common in Ruidera as well as in some sections in the lower river and tributaries.

4.2.6. Management and Conservation Management problems in the Guadiana catchment are mostly related to the scarcity of water in the face of high water demands. The better-protected areas are in constrained sections in Portugal and in the upper Guadiana (Ruidera and Tablas de Daimiel) along with streams having poor access. The upper Guadiana suffers from water resource exploitation. A progressively greater water abstraction in the 60s and 70s caused aquifer 23 to level off at <35 m (Bromley et al. 2001), and a pumping rate >2/3 of the maximum historical rate (400 Mm3/year) was found unsustainable (Fornes et al. 2000). Aquifer 23 was officially declared overexploited in 1994, and complete recovery would require the total cessation of water extraction for 5–15 years or at least the implementation of sustainable irrigation practices (Bromley et al. 2001). Regulations are difficult to enforce because of resistance by farmers that use irrigation for crops. Other impacts to the river are related to water extraction (Fornes et al. 2000). For example, groundwater depletion has sharply decreased surface flows in the Guadiana, Zancara and Gig€ uela over the last 30 years (Alvarez Cobelas 2006). This is particularly noticeable during dry periods in the upper Guadiana. The drying of several km of the upper Guadiana over 15 years caused severe damage to riparian forests. Here the water table was lowered by 30– 40 m below the river channel, the river flowing only in a wet period in 1995/1996. Historically, wetlands covered 250 km2 of the catchment, but only 70 km2 remain today. Most wetlands were drained for agricultural lands. Some wetlands are now on the RAMSAR list or have been classified as National or Regional Parks. In 1981, UNESCO designated the Tablas de Daimiel wetlands as a Biosphere Reserve due to its ecological importance. The Tablas de Daimiel is now a National Park and is an area of special concern under RAMSAR and ZEPA agreements. The declaration of Tablas de Daimiel as a National Park forced an emergency resolution to conserve its aquatic habitats, in which 30 Mm3 per year is diverted from Tagus-Segura to Guadiana-Gig€ uela and, therefore, to the Tablas. In the middle and lower Guadiana, human impacts are expressed in the poor state of river habitat and riparian vegetation. A river survey evaluating riparian vegetation, estimated that about 80% in the Gig€ uela, 94% in the Zancara, 8% in the Z ujar and 15% in the Guadiana were in a poor or degraded condition (CH Guadiana 2002). In many areas,

PART | I Rivers of Europe

especially in arid lands, riparian vegetation practically does not exist because land use extends to the riverbanks. In the lower river, the ‘Castro Marim’ salt marsh is a Natural Reserve encompassing 2090 ha of tidal influenced land. It is an important nursery area for fish, molluscs and crustaceans and habitat for large birds including storks and flamingos. The Guadiana is a highly regulated river. In Spain, the Guadiana has 86 reservoirs >1 Mm3, with an overall retention capacity of 9114 Mm3 (CH Guadiana 2002). In Portugal, 13 dams have been built on the Guadiana basin, the largest being Alqueva. When completely filled, the Alqueva will be the largest reservoir in Europe, covering an area of 250 km2 and (among other consequences) will threaten the habitat of the few remaining Iberian lynxs.

4.3. THE GUADALQUIVIR The Guadalquivir derives its name from the Arabic word wadi al-Kabir (‘large river’), whereas the Romans named it Betis. The catchment area of the Guadalquivir is 57 527 km2. The catchment includes a well-defined geographical depression, bounded by the Sierra Morena range in the north, the Bethic range in the south, and the Atlantic Ocean in the southwest. Most of the Guadalquivir network (90.2%) drains through Andalucia, with smaller tributaries draining parts of Castilla-La Mancha, Murcia and Extremadura. The Guadalquivir has a complex catchment, resulting from the orography and configuration of the depression and surrounding mountain ranges. The Guadalquivir headwaters are in the Canada de las Fuentes at 1350 m asl in the Cazorla range. The river flows southwest, merging with the Aguascebas on the left and further downstream with its largest tributary Guadiana Menor (area 7251 km2), and then Guadalbullon. The Genil enters the lower river and has a catchment 8278 km2. The headwaters of the Genil are in Sierra Nevada and it later flows through the city of Granada. After Guadiana Menor, the Guadalimar enters from the right, and further downstream enter Jandula, Yeguas and Genil from the left and Bembezar from the right. In the lower river, Guadiamar and Arroyo de la Rocina (from Donana National Park) enter from the right and Corbones, Rivera de Huelva and Guadaira from the left. The middle and lower Guadalquivir flow through large cities such as Cordoba and Sevilla, and is navigable to the mouth. In the estuary, the river divides into several arms and forms a marsh called Marismas del Guadalquivir with Donana National Park to the west. The Guadalquivir enters the Atlantic Ocean by the city of Sanlucar de Barrameda, a historical trade harbour between Spain and America.

4.3.1. Historic Changes Agriculture, forestry and mining have a long history in the catchment. Early signs of mining (silver and copper) date back to 3000 BC. Mining was intense during the Phoenician

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PHOTO 4.2 Guadalquivir River at Cordoba (Photo: Sergi Sabater).

and Roman periods, and again in the 19th century. Copper and silver attracted the Romans, who also tended olives and vineyards. Humans have caused major alterations in vegetation and land use; especially visible in the landscape of Jaen and Cordoba. A former landscape of evergreen oaks (Quercus rotundifolia Lam.) is now replaced by olive trees and other extensive crops. The natural vegetation has been reduced to small areas.

4.3.2. Biogeographic Setting Although variable, a Mediterranean climate influences the entire catchment. Well-preserved patches of evergreen oak forest are found in Sierra Morena, in protected areas of Sierra de Aracena and Picos de Aroche (Huelva), Sierra Norte in Sevilla and Sierra de Hornachuelos (Cordoba). On siliceous and more humid soils grow cork oak Quercus suber, forming a dense forest, especially in the GuadaleteBarbate, Sierra Morena and Aljibe ranges. In drier areas, pines (Pinus halepensis) grow, especially in lowlands of the Bethic range and in the Guadiana Menor basin. Climate variation in the catchment is also evident by the presence of Andalusian fir (Abies pinsapo), an endemic species that thrives in a few humid areas having shade and moderate temperatures.

4.3.3. Physiography, Climate and Land Use The Guadalquivir catchment has three main physiographical units: the Sierra Morena range, the Bethic range, and the Guadalquivir valley. The northern Sierra Morena is 400 km long and has an east–west formation that abutts the Meseta bedrock. Paleozoic bedrock rises in the north with some mountains >1000 m asl (Sierra Madrona; 1323 m asl; Almaden; 1107 m asl, Aracena; 912 m asl). The southern part of the range determines the flow direction of rivers with constrained channels in a saw-like landscape. The Cambric carbonates of Cazorla and Sierra Morena have important subterranean aquifers. In this area, cattle predominate because of limited agricultural soils and low human density (18 inhabitants/km2). The area has a high annual rainfall that gradually decreases towards the east. The catchment contains a number of small lakes and wetlands (Guerrero et al. 2006). The Bethic range in southeast of the catchment is one of the largest geologic structures on the Iberian Peninsula. Orogenic activity caused deep limestones and marls to be folded in two parallel ranges (the Prebethic and Subbethic ranges) with an intermediate depression (the Penibethic Depression) in between. The same activity formed the Guadalquivir Depression. The Guadalquivir has its headwaters in the Prebethic range. The headwaters of the Genil and the Guadiana

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Menor are in the Penibethic Depression. High erodibility and estepary vegetation in this region allow gully-type watercourses in the Genil and Guadiana Menor watersheds. These rivers drain the widest and better-preserved badland landscape of the Iberian Peninsula (Teran & Sole Sabarıs 1978). The Guadalquivir Depression is a wide triangular plain (150 m asl on average, 330-km long, 200-km wide in its lower part) with an Atlantic influence. The Depression was formed after the Alpine foldings and later filled with Tertiary marine sediments. Gentle hills are the predominant landform in the Guadalquivir Depression. Most of the Guadalquivir catchment is characterised by a warm temperate (Mediterranean) climate with mild temperatures (annual average 16.8  C) and a relative paucity in rainfall (annual average 630 mm). In the Guadalquivir Depression, maximum summer temperatures may reach 50  C (average is 40  C) and is one of the warmest areas of the Iberian Peninsula. In the north, the Sierra Morena has average annual temperatures between 14.5 and 16.5  C, while air temperatures range between 11.5 and 14  C in the Cazorla range. Lowest temperatures occur on north slopes of the Sierra Nevada and in the Genil headwaters, which are snow-covered during winter. Frost is rare, except in the Bethic range, and day light totals 2500–3000 h per year. A characteristic of the Guadalquivir climate is dry summers (rainfall <10 mm), and wet winters. The openness of the catchment to the Atlantic Ocean allows the influence of western storms that create a southwest/northeast gradient in rainfall with highest rainfall in the mountains (up to 1700 mm in Aracena and Cazorla). Rains are highly irregular and usually torrential, typical of the Mediterranean regime. High rainfall also occurs in mountains of the Sierra Nevada that are exposed to the Mediterranean. This Ocean influence causes more rainfall in Guadalquivir than in the nearby J ucar and Segura catchments. Minimum rainfall, around 300 mm annually, occurs in the Bethic highlands.

PART | I Rivers of Europe

the Genil, flows range from 0.0 to 3342 m3/s. The usual low flow in summer can also extend into other periods of the year such as in 1990–1991 when flow was nil for most of the year (Figure 4.2). The middle and lower Guadalquivir have conductivities between 700 and 1400 mS/cm with values decreasing in summer (May-September). The Genil and Guadaira have the highest conductivity of the Guadalquivir tributaries (CH Guadalquivir data), averaging 2163  670 mS/cm in Guadaira from 1994 to 2005. The Guadaira is saline in its headwaters because of high evaporation. In the estuary, water conductivity is highest in May–September because of a marine influence. Freshwater inflow in the lower river is strongly regulated by the Alcala del Rıo dam about 110 km from the river mouth. In this section of the river, water temperature is >22  C from May to October and can reach 26  C in July. Minimum average temperatures are 12  C in December–January. Water quality of the Donana marshs is influenced by sediment deposition, eutrophication and heavy metal pollution. In particular, the eastern Donana is affected by low quality incoming water and a general increase in nitrate has been detected in the marsh (Serrano et al. 2006).

4.3.4. Geomorphology, Hydrology and Biogeochemistry The floodplains of most rivers in the Guadalquivir catchment have been transformed into agricultural land. Lateral arms, meanders and wetlands have been channelized or drained and converted into agricultural land such as rice fields and orchards. Just recently, an extensive riparian corridor has been restored in the catchment (Marın Cabrera & Garcıa Novo 2005). The Guadalquivir has a highly variable flow regime. Runoff coefficients range from 15% in the Guadiana Menor and Jandula to 24% in the Genil and 29% in the Corbones. Annual discharge in the Guadalquivir is 7230 Mm3 (229 m3/s). The Genil and Guadiana Menor contribute 29.4 and 15.7 m3/s, respectively. Discharge in the lower Guadalquivir ranges from 0.09 to 1640 m3/s. At the confluence with

FIGURE 4.2 Long-term discharge patterns of selected Iberian Rivers.

Chapter | 4 The Iberian Rivers

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Some tributaries transport large concentrations of suspended solids associated with the high erosion and aseasonal runoff. This effect is particularly evident in rivers draining the left side of the catchment and those of the Sierra Morena. For example, average suspended solids in Guadiana Menor were 1064  6046 mg/L in 1994–2005, with maximum values >50 000 mg/L in spring and fall. Lowest suspended solids occur in the tributaries from the right side of the catchment and those in Sierra Nevada. In the main river, TDS range between 60 and 800 mg/L, but values may reach 3600 mg/L in certain areas and times of the year. Some areas in the Guadalquivir catchment contribute major inputs of industrial and, especially, urban effluents. The most effected tributaries and reaches are the Guadiel (at Bailen), Guadalbullon (receiving the waters from Jaen), Guadaira, Genil (downstream of Granada), Guadalete (at Jerez), and Guadalquivir (downstream of Cordoba and Sevilla). For example, the Genil had average values of 4.24  6 mg/L PO4 from 1994 to 2005. In areas with intensive agriculture and farming (irrigated crops and livestock), high nitrate concentrations (from 20 to 67 mg NO3 L 1) characterize surface and ground waters (Figure 4.3). Olive pressing produces a residue called alpechin that constitutes one of the major organic pollutants in the catchment. Alpechines cause high levels of nitrate, ammonia and phosphate in receiving waters. The effluents of alpechin in Andalusia in the past were equivalent to 6.3 million inhabitants, but this presently has been reduced with the introduction of novel environmentally friendly technologies.

4.3.5. Aquatic and Riparian Biodiversity The Donana marshes are distinct from the estuary and could be considered as an interior delta. The marshes are a wide, open area, covering 27 000 ha with an impermeable clay substrate that retains rainwater. The hydrology of the system is complex, with a 6-month receiving/storage period, followed by 2 months water retention from flooding, then a dry period in summer (Garcıa Novo et al. 2007). The hydrology influences the water chemistry of the various water bodies over time (Montes et al. 1982). A marine influence is limited to small areas. The area also is geomorphologically diverse with permanent waters (lucios or round ponds), river channels and inundated shallow but temporary marshes. The marshes retain a high biodiversity. The Donana host a cosmopolitan flora of diatom and filamentous algae. Planktonic communities are made up of nanoplankton, in which flagellates and euglenales are most common. Also common are iron-fixing taxa such as Tribonema, Trachelomonas, Oedogonium and Bulbochaete (Margalef 1977). The presence of Anabaenopsis is related to nitrogen-limited waters. Salinity is associated with the presence of Nodularia (Cyanobacteria), and Cylindrotheca, Nitzschia, Chaetoceros and Campylodiscus (Bacillariophyta). Crustaceans are the most abundant

zooplankton (Marın Cabrera & Garcıa Novo 2005) with Diaptomida at 13 taxa, Cladocera at 50, and Rotifera at 80 taxa. Zooplankton communities are, in general, made up of circum-mediaterranean taxa, some of them with a North African distribution (Diaptomus kenitraensis, Copidiaptomus numidicus, Hemidiaptomus maroccanus). The diaptomid Dussartius baeticus and rotifer Lecane donyanensis are local endemics (Marın Cabrera & Garcıa Novo 2005). The isopod Asellus coxalis and ostracod Isocypris beauchampi are particularly special taxa to these waters. The estuary is also an important breeding and nursery ground for many marine species.

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The rivers Tinto, Odiel, and Guadiamar contribute high levels of heavy metals to the estuary and its sediments (Cabrera et al. 1987) that directly influence its flora and fauna. These rivers drain a major part of the Iberian pyrite belt, a massive sulfide deposit in southern Spain and Portugal (van Geen et al. 1999). The estuary is inhabited by iron-oxidizing bacteria, sulphur-oxidizing bacteria and filamentous fungi (Lopez-Archilla & Amils 1999). Their activity causes high concentrations of iron, copper, zinc and lead in the water. In spite of the acidity of the waters, a luxurious algal community and various animals inhabit the river (Sabater et al. 2003). Riparian vegetation along permanent channels of the Guadalquivir is somewhat independent of the local climate, providing a higher humidity even in dry areas. Willows (Salix atrocinerea, S. alba) and aspens (Populus nigra), as well as other deciduous trees, are common riparian vegetation. A large number of Ephemeroptera taxa is found in the upper Guadalquivir, (Alba-Tercedor et al. 1992). In the headwaters of the Genil, Coleoptera, Trichoptera and Ephemeroptera are common. In seasonally dry rivers with permanent flowing sections, there is an even balanced assemblage of Ephemeroptera, Coleoptera, Trichoptera, Odonata and Heteroptera. In periodically dry rivers, the channel comprises a series of ponds (such as those occurring in the Guadaira), and lentic species of Coleoptera are most common (Alba-Tercedor et al. 1992). Small streams, particularly in the Sierra Morena and Bethic ranges, are open-canopied and temporary, causing initial heterotrophic conditions to shift to autotrophy (Molla et al. 1994). Flow regulation can affect the life cycles of macroinvertebrates in the Guadalquivir. For instance, significant changes in the diet of the mayfly Rhyacophila nevada were related to changes in flow hydrology that altered resource availability (Bello & Alba-Tercedor 2004). The red-swamp crayfish (Procambarus clarkii) was introduced to Guadalquivir marshes in 1973 for commercial reasons, and is now a common invader in Iberian waterbodies, especially in the south. The increase of this invader coincided with a decline in the native white-clawed crayfish (A. pallipes). It was observed that P. clarkii inhabits the lower and middle reaches of rivers up to 820 m asl, whereas the native whiteclawed crayfish inhabits the upper reaches and may persist following invasion (Gil-Sanchez & Alba-Tercedor 2002). There are 29 fish species in the freshwater reaches of the Guadalquivir, and the Iberian chub (S. pyrenaicus) is an Iberian endemic. This species is found in central and southern catchments of the Iberian Peninsula (Doadrio 2001), inhabiting all kinds of flowing waters. S. pyrenaicus is an omnivore (Blanco-Garrido et al. 2003), a characteristic feeding habit in seasonal environments (Magalh~aes 1993). In the estuary, the number of fish species increases to 70 (Drake et al. 2002).

resources within the basin are 3357 Mm3/year and the total water demands equal 3598 Mm3/year. The water demand is high and leads to water scarcity when rainfalls are low. River regulation affects the main river and all large tributaries. There are 55 dams in the basin (one every 160 km), with a potential water storage of 7109 Mm3. The regulated water volume equals 51% of the surface water resources and 55% when groundwater resources are included (CH Guadalquivir, unpublished report). The Guadalquivir marshes are the most severely impacted area in the catchment because of agricultural and urban activities. The marshes covered 136 000 ha into the 1950s, but after much of the marshland were converted to farm and agricultural lands. The marsh system is controlled by a series of dikes and drainage canals, and the marshes are now under restoration and monitoring (Gallego Fernandez & Garcıa Novo 2002). Pollution is a major problem in many parts of tributaries and the main river. Water treatment is still limited to larger urban areas, and smaller cities and villages still add untreated sewage waters directly to adjacent watercourses. Other pollution sources are related to industry and mining. In the Jandula, some pollution is associated with hydrocarbons from oil processing. Mining activities have also caused significant impacts in the watershed. A retaining dike of a mine tailings reservoir failed in Apri1 1998 in the Guadiamar catchment that released 5 Mm3 of toxic sediments and water into the river near Donana National Park. The released sludge contained 0.6% arsenic, 1.2% lead and 0.8% zinc dry weight (Pain et al. 1998), and cumulated as a several centimetre thick layer along 40 km of the river (Grimalt et al. 1999). Mine tailing residue was found in periphyton (Sabater 2000, Martın et al. 2004), macroinvertebrates (Sola et al. 2004), fishes and waterfowl, as well as in water and sediment. An immediate cleaning of the entire area, including riparian and agricultural land and stream sediments, probably reduced the effect and allowed a quick recovery of the system (Montes 2002). The present heavy metals situation for aquatic systems of the Guadiamar is good with no observed systems being contaminated (Sola et al. 2004). Indeed, the mining accident and its follow-up triggered major programs of monitoring and recovery for the Guadiamar and Donana marshes. The Spanish administration developed the Donana 2005 Project as well as Green Corridor of the Guadiamar (Garcıa Novo et al. 2007). Both aim to restore the ecology of the affected areas and facilitate the biological connectivity between the Donana and Sierra Morena.

4.3.6. Management

The Duero (Douro in Portuguese) is in the northwest Iberian Peninsula. It is the 3rd largest river (after the Tagus and Ebro) in length (927 km, 597 in Spain and 330 in Portugal) and the largest in catchment area (97 290 km2, 80% in Spain and 20% in Portugal). The river originates in the Iberic range

Water regulation has always been viewed as the only possibility to improve the management of the Guadalquivir River because of its overall water deficit. The available water

4.4. THE DUERO

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PHOTO 4.3 Duero at Soria (Photo: Sergi Sabater).

at Picos de Urbion (2140 m asl) and flows west towards Portugal, reaching the Atlantic Ocean at the city of Oporto. The Spanish part of the Duero catchment drains the Cantabric Mountains in the north, the Iberian Mountains in the east, and the Carpetovetonic Mountains in the south. The river flows through the cities of Soria and Zamora. At the border of Spain and Portugal, the Duero flows through a deep valley and enters the Atlantic via a simple estuary with a sedimentary deposit along the south margin that forms Cabed^elo do Douro. Major tributaries include the Pisuerga and Esla on the right and the Eresma and Tormes on the left. The Tormes flows through the cities Avila and Salamanca. Downriver in Portugal, the Duero receives the T^amega, Sabor, Tua,  Agueda and Coa. The right-side tributaries in Portugal are larger than the left-side tributaries.

4.4.1. Historic Changes and Human Impacts Paleolithic remains are evident on the Duero and Pisuerga floodplains as well as on the banks of the Coa. The first fortified settlements in the coastal Duero area are from the 10th century BC (e.g. Cit^ania de S.Juli~ao). The Celts colonized the Meseta along the river network 900 BC. Paleobotanical records show a decrease in forest cover for agriculture and livestock use already in the 10th century BC. During the Roman period, urban development, mining, agriculture and road construction caused major effects on the natural environment. By 430 AC, the Sueves had established themselves in the Douro basin in Portugal. In the Middle Ages, cavalry development was responsible for the desert fields such as Tierras de Toro y Campo near Zamora. Remains of Roman architecture are evident in the Duero catchment, with many churches from the 12th–13th century.

During the 15th–17th centuries, livestock were intensively used on the catchment. In the 20th century, rural population sharply decreased and moved into urban areas. Today, the area around the river mouth has a high human density (1462 inhabitants/km2) and a high density of small industries.

4.4.2. Biogeographic Setting The Duero catchment has Atlantic, Mediterranean and Alpine influences and lies in the Ibero-macaronesian ecoregion. About 17% of its surface area is forest and 25% is thicket. The most common tree in the catchment is Quercus ilex, the subspecies ilex in the northeast and rotundifolia elsewhere. Quercus pyrenaica is also abundant, especially in the Cantabrica range where it inhabits montane areas and other high elevation areas of the central plain. Pine forests cover the central plain of the Duero catchment where Quercus forests have decreased. The Mediterranean Juniperus thurifera grows on carbonate soils. The Euro-Atlantic oaks Quercus robur and Quercus petraea are found on the Cordillera Cantabrica, mixed with Fagus sylvatica, Castanea sativa and Pinus sylvestris. Fagus sylvatica dominates forests on acidic soils and temperate slopes at 1200–1700 m asl. Castanea sativa forests are found along Sanabria Lake and southwest of Leon. Thickets of Erica australis and Sarothamnion scoparia occur in the Iberic and Central ranges following deforestation. Riparian forests consist of Populus sp., Alnus glutinosa, Ulmus sp., Fraxinus sp. and Salix sp. The present configuration of the Duero catchment is a result of historic geological processes. The amphitheatre defined by the mountains surrounding the catchment, contains sediments from the ancient lake formed in the Tertiary.

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Quaternary glaciers covered most headwaters of the Esla, Duerma, Eria and Tera. The glacier in the Tera valley was the largest, being 5 km long. Today, several moraines are evident near Sanabria lake. The upper Pisuerga and Carrion also show effects of glaciation. Towards the Atlantic, the Hercinian massif formed the Zamora and Salamanca highlands as well as mountain ranges in north Portugal. Most of the catchment is in the northern Meseta, mostly above 800 m asl, and the highest in the Iberian Peninsula. The Duero catchment has had a progressive lowering of its surface since the Miocene, causing the loss of some former tributaries to the rivers Ebro, Sil and Tagus, and a reduction in its area.

4.4.3. Physiography, Climate, and Land Use In the headwaters, the Duero flows over Cretacic materials, later replaced by Tertiary materials as the river flows through Soria. After Zamora, sediment deposits are composed of slates, siluric quarcites and granites. The lower river flows over granitic, metamorphic and paleozoic rocks. In Portugal, the catchment is in the Hesperic Massif, mainly made up of granites and schists. The Pisuerga and Esla flow over a diverse lithology. Their headwaters originate on carbonate and devonic soils, later flowing over cretacic and liasic soils, and finally over quaternary soils with miocenic deposits. The lower Esla and the Tera flow over siluric, crystalline and granitic soils, which form the basin of the glacial Sanabria Lake. In the central Duero basin and left bank of the river, soils have a sandy texture. Here the substrate is sandstones, conglomerates and detritic limestones, in addition to fluvial deposits of conglomerate, gravel and sand. The Duero catchment has a Mediterranean climate, although in the most eastern part the climate is more continental. Near the Portuguese border, the climate becomes milder because of Atlantic influences. Winters are long and cold, especially in septentrional Meseta where average temperatures are 2  C and frost occurs for 120 days per year. In the west, winters are milder (mean January temperature is 4  C and on average 80 frost days per year). Intense cold waves (from 13 to 20  C) are associated with invasions of continental polar air from the northeast. Summer maximum temperatures (July) occasionally reach 30  C, but in the north reach only 20  C. Highest rainfall occurs in the upper Tera (>1800 mm year) and Porma (1500 mm/year). Annual precipitation decreases to 800–1000 mm in the Central and Iberian ranges, and even more so in the plains (400– 550 mm). Rainfall is irregularly distributed in the year, but mostly occurring from autumn to spring and being nearly absent in July and August. Interannual variability is even more extreme with average annual rainfalls ranging from 350 to >800 mm. Average evapotranspiration ranges between 675 and 730 mm per year. There is a strong gradient in precipitation from the Spain/Portugal border to the Ocean. The mean annual evapotranspiration and precipitation are

PART | I Rivers of Europe

<400 mm near the border, but evapotranspiration increases to >800 mm and precipitation up to 2000 mm per year on the coast. The population in the catchment is mostly in mediumsized cities (Leon, Burgos, Valladolid). There are many villages with <1000 inhabitants and few have 50 000. Most of the catchment is covered by forest and agriculture. The central region (700–800 m asl) has undergone an intensive process of agricultural exploitation over time with a predominance dry farming such as cereals (wheat, oats and barley) and vineyards. The little forest cover is composed of Q. ilex var ballota and Pinus pinea. In Portugal, vineyards are especially important (Porto wine) in the catchment. Recently, agriculture has become less important and many agricultural fields have been abandoned, whereas industrial activity of chemicals and metals as well as production of electricity has increased.

4.4.4. Geomorphology, Hydrology, and Biogeochemistry The main river channel is 572 km long. The first 72 km flows through steep valleys in the Iberic range with an overall slope of 14. The remaining 500 km of the river meanders through an open valley over soft tertiary sediments (slope 1). At the border (rkm 112), the river has a canyon shape (Canones de Arribes) with a mean slope of 3. The 402 m drop in height has been used to produce hydroelectrical power via several hydroelectric  dams in both countries. From the confluence with the Agueda River to the mouth at the ocean (213 km), the river flows through narrow valleys and has a low gradient (0.6 m/km). The upper reaches have a nivopluvial flow regime with an oceanic influence. However, there is a strong relationship between rainfall and hydrology of the river. Maximal discharge occurs in spring and minimum in summer, but differences are not extreme. Major floods can occur in the Duero due to intense winter rains, although floods can also occur at late summer because of heavy storms. High discharge periods, such as in January 2006, are usually correlated with peaks in suspended solids. Discharge in the middle reach averages 101.2 m3/s (Duero at Zamora, 12 year average). Among the tributaries, the Esla and Pisuerga have the highest discharge and the Adaja has a mean discharge of 11 m3/s. Mean flow near the river mouth is 903 m3/s (Figure 4.2). The mean water temperature ranges from 11.2  C in the headwaters to 14  C at Toro and in the lower Tormes (12 year average). Minimum temperatures range from 0 to 2.8  C (in Pisuerga headwaters and Duero at Toro and Tormes). Maximum water temperature ranges from 21 (headwaters) to 28 (at Adaja river). The geology of the catchment causes a low mineralization of its waters. The Pisuerga has the highest conductivity, while the Esla and Tormes the lowest. Conductivity increases along the main channel (from 128 mS/cm at Garray to 582 mS/cm at Toro) due to water from the Pisuerga (562 mS/cm). Most headwaters in the catchment have a

Chapter | 4 The Iberian Rivers

low nutrient content (Fernandez-Alaez et al. 1986, Escudero Berian et al. 1986) and increased nutrient concentrations in rivers are related to human activities (urbanization and agriculture). Low nutrient concentrations and conductivities characterize the upper Tormes and Eresma (10–16 mg/L N–NH4, 15–23 mg/L P–PO4, 700–800 mg/L N–NO3, and 16.2–67.5 mS/cm). In the alluvial aquifer of the Pisuerga, irrigation and industry have degraded groundwater quality as well as the seasonal recharging of the aquifer (Helena et al. 2000). Waters in most tributaries and the main channel have high nitrate levels (2.5–2.6 mg/L) and relatively low phosphates (Figure 4.3). There is a trend of decreasing phosphate and ammonium levels, but not nitrate, in the last 12 years. Reservoir outflows have caused significant increases in nutrient concentrations and in benthic algal biomass (Camargo et al. 2005). Contamination episodes in the Duero have been related to timber industries in the catchment. Most of the chemicals used to improve wood properties produce toxic effects on aquatic fauna. However, dissolved oxygen values <6 mg/L have not been recorded recently, and nearly 75% of the rivers are classified in good condition using biotic indices. The trophic analysis of lakes and reservoirs on the Duero (CH Duero 2004) indicate that Sanabria Lake and several reservoirs are oligotrophic. Lake Sanabria has low chlorophyll values (1.9 mg/L) with a phytoplankton dominance of cryptophytes and small chlorophytes (Negro et al. 2000). Most oligotrophic or oligo-mesotrophic reservoirs are in the north Duero catchment, especially in the upper Pisuerga, Carrion, Esla and Orbigo. These reservoirs also have low chlorophyll (<4 mg/L), phosphorus and nitrogen contents. The most eutrophic and hypertrophic reservoirs are in the south Duero catchment, and are typically small and affected by urban inputs. Reservoirs on the main channel are also eutrophic, and 70% of the reservoirs can be classified as mesotrophic. In several reservoirs (13 of the 40 monitored by the CHD), a significant growth of cyanobacteria was evident. In Portugal, diffuse pollution is moderate and the pollution load is limited to some agricultural industries.

4.4.5. Aquatic And Riparian Biodiversity Riparian vegetation in the catchment has diverse distributions. In areas where phreatic levels are high but rarely inundated, willows (Salix spp., Salix alba), oaks (Quercus pyrenaica), elms (Ulmus minor), and spiny plants (Rubus ulmifolius, Crataegus monogyna, Lonicera spp., Prunus spona and Rosa spp.) dominate. In upper mountain areas, riparian vegetation is dominated by Betula pendula, Prunus lusitanica, Reseda gredensis and Biscutella gredensis. In torrential siliceous streams that dry in summer, buckhorns (Flueggea tinctoria) may be present. Boxwood (Buxus sempervivens) is dominant on the stony substrate in the Sabor River, the largest unregulated tributary of the Duero in Portugal. In many human impacted areas, the riparian forest is

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dominated by rapidly growing trees such as poplar, and in the middle reach of the Duero, riparian vegetation is scarce due to the agricultural use of river margins (Photo 4.1). Benthic chlorophyll values are low in the upper Tormes and Eresma (5–11 mg/m2), but increase significantly below deep release reservoirs (52–126 mg/m2) (Camargo et al. 2005). Scrapers and collector-gatherers also increase below the dams (Camargo et al. 2005). Macrophytes are quite diverse in the Duero catchment. Macrophytes in the Tormes are characterized by Juncus acutiflorus and Carex hirta at open sites, and Oenanthe crocata, Myosotis scorpioides and Epilobium obscurum at shaded sites (Escudero Berian et al. 1986). The most abundant submerged species are Ranunculus trichophyllus, O. crocata, Apium nodiflorum, and M. scorpioides; depending on current velocity (Escudero Berian et al. 1986). In the headwaters of the Bernesga, macrophytes are dominated by Carex acuta var. broteriana, Agrostis stolonifera and Mentha longifolia, also depending on current velocity (Fernandez-Alaez et al. 1986). Macroinvertebrate richness and biodiversity in the Duero in 1980 showed good quality in most low-order reaches. The index of biological quality decreased after the city of Soria and even more so after the Pisuerga confluence by Valladolid. Biological quality in the middle Duero slightly recovered after Zamora and the inflow from Esla and Tormes (Gonzalez del Tanago & Garcıa de Jalon 1984). In the right-side tributaries in Portugal, the mayflies Habroflebia, Caenis and Baetis, the stoneflies Leuctra spp., chironomids and oligochaeta occur frequently or in large numbers (Gra¸ca et al. 2004). There is a large diversity of caddisflies, including Limnephilidae (e.g. Allogamus ligonifer, Limnephilus guadarramicus, Potamophylax rotundipennis, Chaetopteryx lusitanica), Leptoceridae (e.g. Setodes argentipunctellus, Athripsodes braueri/tavaresi), Hydropsychidae (Hydropsyche siltalai), Philopotamidae, Calamoceratidae, and Sericostomatidae. Stoneflies account for 7 families and 17 species (e.g. Leuctridae, Nemouridae, Capniidae, Perlidae) in two examined streams (Cortes et al. 1998). Two endemic macroinvertebrates are found in the Duero catchment. One is the native crayfish (A. pallipes), and the other is the river mother-of-pearl (Margaritifera margaritifera). This endangered bivalve has been found in some areas in the Tera and Negro (Esla tributary) having low mineralization and cold oligotrophic waters (Morales et al. 2004). Three introduced invertebrate species are important in terms of biomass: the clam Corbicula fluminea, the Louisiana red crayfish P. clarkii and the introduced signal crayfish Pacifastacus leniusculus. The most common fish species in the Duero are Chondrostoma arcasii (living in mountain lakes and rivers associated with Salmo trutta), C. lemmingii (found in rivers in the southeast), Squalius carolitertii, Barbus bocagei (in the entire basin but currently decreasing in abundance), Chondrostoma duriense (endemic Duero fish found in high current rivers and reservoirs), and Cobitis calderoni. In the lower river, the endemic ruivaco Rutilus macrolepidotus, and the

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endangered, vulnerable or rare P. marinus, Alosa alosa, A. falax, S. trutta, B. bocagei and Chondrostoma polylepis are present (Moreira et al. 2002). These Iberian fishes are threatened by the introduction of exotic species such as sunfish, American perch, carp, red fish and gambusia. Reservoirs also impede fish migrations and create unsuitable habitat conditions for riverine fish. Other abundant fishes are trout, pike, tench and Gobio gobio. Trout (S. trutta fario L.) show two genetically divergent groups in the catchment (north and south) that suggest successive colonizations after the Pleistocene glaciations (Bouza et al. 2001). Sixteen species of amphibians and reptiles have been recorded in the catchment. Particularly important is the Lusitanic salamander Chioglossa lusitanica in areas with precipitation >1000 mm. Other endemic species are Triturus boscaii, Discoglossus galganoi, Alytes cisternasii and Rana iberica. The cliffs of Duero International Park along the border with Spain (Arribes del Duero) are an important nesting area for the griffon vulture, Egyptian vulture, peregrine falcon, golden eagle, black kite and hen harrier. The white stork, black stork and Chough also are frequent in this area. In fast flowing waters of mountain streams, water birds are uncommon except for the dipper. An interesting mammal of the Duero in Portugal is the water mole; an Iberian endemic found only in unpolluted flowing waters.

4.4.6. Management and Conservation The largest reservoir in the catchment is La Almeda on the Tormes with a storage capacity of 2586 Mm3. The most important water use in the catchment is irrigation that requires >3603 Mm3/year, whereas urban supply uses 214 Mm3/year and industry 43 Mm3/year. Nearly 10% of the water demands are met by groundwater. The hydrological plan of the Duero basin (1998) assigned 645 Mm3/year downstream to the main reservoirs for environmental objectives. Many shallow lakes are found along the main channel, especially in the central region. These lakes are classified as ‘natural spaces for special protection’, and include Isoba and Ausente lakes (in Leon), Laguna Negra (a glaciar lake in Soria), Lagunas de Villafafila (in Zamora), and Fuentes Carrionas (in Palencia). The last two are also wildlife reserves. The Natural Park of Lago de Sanabria and its surroundings include the largest glacial lake of the Iberian Peninsula (369 ha) and many dispersed lagoons hosting patches of Sphagnum, as well as glacial canyons and valleys. This Natural Park is included in the Natura 2000 network. The Natural Park of Arribes del Duero includes the canyon of the river Tormes and its surroundings. This area has been declared a special protection zone for birds (ZEPA) since 1990. Montesinho Natural Park is at the source of one of the most important and best preserved tributaries of the Duero, the Sabor. Lastly, Alv~ao Park is an area aimed to protect several endangered mammals and its rivers are probably some of the best studied in terms of aquatic invertebrates and fish. The

PART | I Rivers of Europe

Duero river basin authority in Spain is the Hydrogrologic Basin Authority of the Duero (CHD). It was created in 1927 to administer the use of water for irrigation and hydroelectric power, and currently manages water planning, water quality, flood prevention, environmental issues and water rights. Spain and Portugal have an agreement (Convenio de Albufeira signed in 1998) created to manage all river basins shared between the two countries.

4.5. THE EBRO The Ebro catchment is in northeast Iberian Peninsula and covers 85,362 km2. Most of the catchment is in Spain with some of it in Andorra and France (445 and 502 km2, respectively). The Ebro is the largest Iberian river flowing into the Mediterranean Sea and is the largest catchment in Spain, encompassing 17.3% of its surface area. The catchment is delimited by the Cantabric Mountains and Pyrenees in the north, the Iberian range in the southeast, and the Coastal Catalan Mountains in the east. Historically, the river originated at Fontibre (from the latin Fontes Iberis, Springs of Iberia) at 880 m asl near Reinosa in Cantabria. Today, the river source is at 1980 m asl in Penalara (27 km upstream from Reinosa). The main river is 910 km long and flows northwest to southeast from the Cantabrian Mountains to its delta at the Mediterranean Sea. Major tributaries include the Aragon, Gallego, and Cinca-Segre from the Pyrenees and Cantabrian Mountains and the Oja, Iregua, Jalon, Huerva, and Guadalope from the Iberian range. The total drainage network equals 12 000 km. The main channel flows near the Iberian range. The Ebro catchment includes one of the largest depressions on the Iberian Peninsula besides the central Meseta. The delta covers 330 km2, 20% of it being a natural protected area and the rest being urban and agricultural land. Rice is the most significant crop. The catchment contains several small lakes, mainly in the Pyrenees, including the karstic lake of Montcortes. Several endorheic lakes are also scattered (Sarinena, the brackish lakes of Chiprana and Gallocanta) in the middle and lower basin. Both freshwater and brackish lakes are significant in the delta region. The Ebro is subject to regulation by many reservoirs. The most important reservoirs are in the lower catchment (Flix, Mequinenza and Ribaroja) that reduce sediment transport to the delta (Photo 4.4).

4.5.1. Historical Perspective The Ebro flows through the regions of Cantabria, Castilla, Leon, Rioja, Navarra, Aragon and Catalonia. The most significant cities, historically, along the Ebro are Miranda de Ebro, Haro, Logrono, Tudela, Alagon, Zaragoza, Caspe and Tortosa. The catchment was inhabited since the Paleolithic. Prehistoric records are evident in the Pyrenees and prePyrenees with remnants of dolmens and megalithic graves,

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PHOTO 4.4 Upper part of the river Ebro River in Haro (Photo: Sergi Sabater).

as well as in the Iberian range in the Guadalope basin. Ibers and celts inhabited the catchment from 15th to 3rd century BC. About 200 BC, the romans colonized from the south, settling in cities such as Zaragoza, Huesca and Teruel. The Arabs arrived on the Peninsula in 711 AC, settling in the cities Zaragoza and Tortosa that were connected by the Ebro. Irrigation ditches were dug and iron and copper industries were developed at this time. The Arabs also settled at Tudela, Calatayud, Huesca and Barbastro. The Aragon Kingdom, which occupied most of the catchment, began 1000 AC. During its history, the Ebro played an important role as a frontier line and also as a communication link. The Ebro catchment was the scene of many bloody battles, such as those in the lower basin in the Spanish Civil War (1936– 1939). River hydrology played a military role during this battle, with sudden floods from upstream reservoirs to interrupt infantry crossings. Agricultural development and navigation needs resulted in infrastructure construction after 1400 AC. The Canal Imperial was completed in 1446 and Pignatelli dam was finished in 1789 by the Conde de Arana, Minister of Charles III of Spain. The Canal Imperial was constructed to connect the Cantabric and Mediterranean Seas. While this project was never finished, the channel flows 108 km along the main river from El Bocal (Navarra) to Fuentes de Ebro (Zaragoza).

4.5.2. Biogeographic Setting A broad spectrum of landscapes make up the Ebro catchment, including boreal-alpine coniferous forests, mixed decideuous forests, Mediterranean evergreen and mixed for-

est and shrubs, and semi-arid treeless formations. Paleartic and cosmopolitan species are characteristic along the river valley in the riparian zone. Some species typically found in the headwaters, such as Cornus sanguinea and Brachypodium sylvaticum, are also found along the river corridor. In the floodplain are species of Mediterranean and iranoturanian, iberonorth African, and endemic species typical of arid gypsum substrate. Water availability allows for the close proximity of typical upland species within the depression with those in the riparian zone. Although vegetation in the Ebro catchment is less altered than in other Iberian catchments, forests represent only 3.1% of the potential forested area (Molina Holgado 2002). The Ebro catchment had a long period as a closed intramountain drainage basin resulting from tectonic topography in the Pyrenees, Iberian range, and Catalan Coastal range. In the late Oligocene, a dry climate probably lowered the lake level and prolonged this endorheic basin stage. The Ebro gradually opened to the Mediterranean in the Miocene between 13 and 8.5 Ma. Groundwater flow was important for the formation and evolution of evaporitic lacustrine facies in the Iberian range and Ebro catchment. The hydrogeology of the basin today is similar to that during the Miocene, allowing groundwater and dissolved salts to cumulate in large areas of diffuse discharge and creating lakes where the evaporites would precipitate. Weathering of underlying evaporitic formations caused the catchment to subside during the Tertiary and Quaternary (Benito et al. 1998). Lake sediment analysis (geochemistry and pollen analysis) from the central basin indicates that some areas experienced a more positive water balance than today. These data suggest that the Ice-Age climate in the

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western Mediterranean region was characterized by cold winters with relatively high humidity.

4.5.3. Physiography, Climate, and Land Use The Ebro catchment has a triangular shape with the larger sides being the Iberian range and the Pyrenees. These two ranges converge in the northeast. The internal Ebro depression increases in width from west to east. The topography causes a Mediterranean climate with continental characteristics in most of the catchment, which becomes semi-arid in the center of the depression. The western side (Pyrenees and Iberian mountains) has an oceanic climate. Mean annual precipitation in the catchment is 622 mm (mean from 1920 to 2000) with high monthly and annual variability. Long periods of low precipitation are typical in late autumn and winter, and higher rainfall occurs in spring and autumn. The rainfall is irregularly distributed in the catchment, ranging from 900 mm in the Atlantic headwaters to 500 mm in the southern Mediterranean zone. Extreme values of 3000 mm/ year in the Pyrenees and <100 mm/year in the central plain have been recorded. Long-term records (1916–2000) show no clear trend in rainfall decrease in the catchment, except for a slight decrease south of Zaragoza (CH Ebro 2005). Stromatolithic microbial mats at the delta revealed long-term effects of El Nino Southern Oscillation events (SanchezCabeza et al. 1999), as did sediment records in an endorheic saline lake (Rodo et al. 2002). Air temperatures range from mild in the more oceanic western area to high temperatures in summer and intense cold and fog in winter in the central depression. A northwest-southeast cold and dry wind (cierzo) is characteristic in the central depression, and can lead to soil erosion and salt transport (Sterk et al. 1999). A mild warm wind sometimes occurs, especially in summer, in the opposite direction (southeast–northwest). Nearly half of the population resides in the cities Zaragoza, Vitoria, Logrono, Pamplona, Huesca and Lleida in the center of the catchment. The Pyrenees and Iberian range have low population densities (most areas with <2000 inhabitants). Altogether, 40% of the catchment has a population density <5 inhabitants/km2. Land use has been traditionally agriculture (vineyards, orchards and corn), although a progressive abandonment of rural activities has lead to the regeneration of woodland and forest cover (Gallart & Llorens 2002). Today, industry is an important activity in the basin with hydroelectric production using 8297 m3/s from 340 hydroelectric plants within the catchment.

4.5.4. Geomorphology, Hydrology, and Biogeochemistry In the first 240 km, the river meanders and flows through rocky canyons at high current velocity. Downstream to rkm 510, the river flows through the plain and has many meanders. In the middle reach, tributaries from the Pyrenees are

PART | I Rivers of Europe

larger than those from the right margin. The main tributary from the right is the river Jalon; and those from the left are the Aragon, Gallego, and Cinca-Segre. Tributaries from the Cantabric Mountains and the western Pyrenees have a pluvial oceanic flow regime. Snow retention in the central and eastern Pyrenees causes a nivopluvial flow regime in those streams. The Segre is the longest tributary of the Ebro, and drains the Pyrenees. The Cinca merges with the Segre just before its confluence with the Ebro. Near the reservoir of Mequinenza, the Valcuerna, Guadalope and Matarranya enter the Ebro. The hydrological regime is more continental in the east, while the southeast has a stronger Mediterranean and continental character with no snow. The Mediterranean pluvial regime dominates streams in the Guadalope and Matarranya catchments. The lower Ebro flows through 120 km of canyon meanders and is quite deep. The river widens at Mora d’Ebre and crosses the Catalan Range before reaching the sea as the Ebro Delta. The Ebro itself shows the lowest interanual variation in flow than other Iberian rivers. Groundwater inputs further smooth its flow regime. A groundwater influence is especially notable in the Jalon up to the Matarranya on the right side and the Ega, Arga, Irati and Alcanadre from the left. High discharge occurs on average from October to March because of the oceanic climate, and into May downstream because of snowmelt from the Pyrenees. Low discharge occurs from July to October. Historical flow records at the mouth (mean annual runoff 13 408 Mm3) show a decrease of nearly 40% in mean annual flow in the last 50 years, resulting from a decrease in precipitation and increase in water consumption for irrigation. An increase in forest cover in the headwaters and the associated increase in evapotranspiration may also be related to the lower discharge (Gallart & Llorens 2004). Regulation of the Ebro in the 1960s caused a major change in the discharge pattern by altering flow timing and, particularly, flood peaks (Lopez-Moreno et al. 2002) (Figure 4.2). Batalla et al. (2004) analyzed flow records from 22 rivers before and after dam construction to determine the effects of reservoirs on flow regime. Variability in mean daily flow was reduced in most cases due to water storage in winter and increased flow in summer (related to irrigation). Water temperature ranges from on average 13  C in the headwaters to 17  C in the lower reach, and with a clear seasonal pattern. A slight decrease in temperature occurs in summer in the lower reach due to thermal inertia of water in the reservoirs (Val et al. 2003). An inverse effect is found in autumn and winter. The Ebro has high conductivity because of its geology. An abundance of gypsum is responsible for the high salinity of waters in the Zaragoza area. Conductivity increases from the headwaters (200 mS/cm) downstream to Zaragoza (2500 mS/cm). The Gallego also contributes waters with high conductivity (1600 mS/cm) probably due to gypsum in its lower watershed. In contrast, conductivity is much lower in the Aragon and Segre (450 and 550 mS/cm, respectively). Conductivity decreases below the

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Chapter | 4 The Iberian Rivers

reservoirs (<900 mS/cm), being related to the input of Segre waters and internal processes. The Ebro at Tortosa transports 13 mg/L of suspended solids with peaks reaching 40– 100 mg/L. High levels of suspended solids (3500 mg/L in the Aragon, 14 000 in the Gallego) can occur at times. Transport of suspended solids in the headwaters is mainly related to discharge, while in the middle Ebro upstream of the reservoirs it is regulated by sediment availability (Roura 2004). Dams in the lower Ebro retain >95% of the suspended fine sediment in the river and alter its quality (Vericat & Batalla 2005). In 1998–1999, the organic fraction before dam operation was 9% of the total suspended matter and had a C:N ratio of 13:52, but was 56% of the total suspended matter with a C:N ratio of 6:11 after the dams because of high plankton abundance (Roura 2004). Average phosphate concentrations ranged from 0.08 to 0.27 mg/L P–PO4 in 1980–2004, and decreased to 0.02– 0.06 mg/L (in Tortosa) in 2004–2005 because of the construction of water treatment plants. No significant changes have been observed for nitrate (Figure 4.3). Nutrient loads are high during high flows, but dilution causes NO3 and DOC concentrations to be relatively low and oxygen content relatively high. During low flows, the river receives considerable nutrient loads from point and non-point sources. The lower dilution capacity causes higher concentrations of nitrate and DOC as well as phosphate. Nutrient pollution is a concern in the middle and lower reaches of the river, both related to industrial activities and non-point sources. Nonpoint sources contribute annual nitrate loads of 25 Tm NO3/ day (Torrecilla et al. 2005). Non-point agricultural sources account for 64% of the nitrate loads in this area of the river, while urban and industrial point sources are responsible for 88% of the phosphate and 71% of the DOC loads (Torrecilla et al. 2005). Other sources of pollution are mines in the north, mercury pollution from the chloro-alkali industry, production and use of solvents and chlorinated pesticides, and flame retardants in auto and electrical plants in the middle-lower reaches. Organic compounds on sediments such as polycyclic aromatic hydrocarbons, alkylphenols and polybrominated diphenyl ethers have been detected along the entire river, and DDT and chlorobenzene have been detected at several sites (Lacorte et al. 2006). Bioaccumulation of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) in fish and sediments was detected below the heavily industrialized city of Monzon (Eljarrat et al. 2005). In the lower Ebro, high concentrations (20–225 ng/ L) of atrazine and other pesticides have been recorded, while endocrine–disruptors have been detected at some hot spots in the middle and lower reaches (Lavado et al. 2004). The marine salt wedge in the Ebro delta reaches 25 km upstream, especially in summer, and disappears during high flows in spring. Today, flow regulation favours the persistence of the saline wedge (Ibanez et al. 1999), leading to a decrease in oxygen content and even anoxia (Munoz & Prat 1994). The lower sediment input affects the physical struc-

ture of delta sediments, and is associated with the current regression of the delta.

4.5.5. Aquatic and Riparian Biodiversity Planktonic (riverine) chlorophyll levels range between 10 and 17 mg/L from the headwaters to Zaragoza, and then increase up to 60 mg/L in the meander plain. Below the large reservoirs, river plankton chlorophyll decreases to <10 mg/L (Sabater et al. 2008). The presence of zebra mussels, the abundance of macrophytes and a certain decrease of phosphorus may be the reason for that decrease in chlorophyll relative to historical values. Chlorophyll concentrations in the lower Ebro in the 1990s ranged from 5 to 46 mg/L, with maximum values in spring and summer (20– 45 mg/L) and lowest values in winter (5–12 mg/L) (Sabater & Munoz 1990). Phytoplankton communities in the lower Ebro (last 60 km) were dominated by diatoms and greenalgae (especially in summer), while Cyanobacteria were frequent in autumn (Sabater & Munoz 1990). Asterionella formosa was most common in winter, while centric diatoms such as A. granulata, Cyclotella sp., Skeletonema potamos and Stephanodiscus sp. were dominant in autumn, spring and early summer, and Scenedesmus sp., Coelastrum sp. and Pediastrum sp. were most abundant in summer. Benthic chlorophyll in the main channel is on average 266 mg/m2 in summer and 196 mg/m2 in autumn (Sabater et al. 2008). In summer, floating algae and macrophytes are present in the lower river, at times covering >40% of the water surface. Epilithic diatoms in the upper Segre are dominated by Achnanthidium subatomus, Diatoma mesodon, Cymbella silesiaca, Fragilaria arcus, F. capucina, Gomphonema pumilum, Meridion circulare and Nitzschia pura (Goma et al. 2005). In temporary saline lakes, the phototrophic community is composed of planktonic (Dunaliella sp., Aphanothece sp.) and benthic organisms (Hantzschia amphyoxis) (Comin 1999). The permanent Lake Salada de Chiprana (78 g/L salinity on average) is covered by microbial mats of Microcoleus chthonoplastes (300 mg Chl a/m2) and the charophyte Lamprothamnium papulosum (de Wit et al. 2005). Microbial mats at the Ebro delta are composed of three pigmented layers of phototrophic organisms: an upper brown layer of Lyngbya aestuarii and diatoms, an intermediate green layer of the cyanobacterium Microcoleus chthonoplastes, and an underlying pink layer of purple sulphur bacteria (Sole et al. 2003). A new amoeba species, Vannella ebro, has been isolated from microbial mats from the Ebro delta (Smirnov 2001). Macrophytes are common in the lower river below the reservoirs. The most abundant macrophytes are Potamogeton pectinatus, P. crispus, P. densus, Ceratophyllum demersum, Myriophyllum spicatum and Lemna gibba (Molina Holgado 2002). At the delta, Potamogeton pectinatus is mainly found in freshwater areas, while Ruppia cirrhosa inhabits transitional zones between freshwater and seawater.

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Mixed stands of Zostera noltii, R. cirrhosa and the floating macroalga Chaetomorpha linum develop in saline areas (Menendez et al. 2002). Healthy riparian forests are still found along the Aragon, Arga, Irati, Cinca, Segre and Gallego, as well as in some sections of the Ebro. Riparian species having rapid growth and being well adapted to water level fluctuations are widespread (S. alba, P. alba, P. nigra, Tamarix africana, Tamarix gallica). Forests of Alnus glutinosa only occur in small areas in the northern catchment. Floodplains are colonized by Polygonum lapathifolium, P. persicaria, Xanthium echinatum and Paspalum paspalodes. In Mediterranean tributaries, the macroinvertebrate genera Ecdyonurus, Physella acuta, and Baetis, and Hydropsychidae are abundant. The Mediterranean influence on these systems is reflected by macroinvertebrate taxa (Perla marginata, Hydroptila insubrica and Hydropsyche instabilis) adapted to avoid the impact of floods (Argerich et al. 2004). Macroinvertebrate communities in the lower river comprise an abundance of filter feeders (Hydropsyche, Ephoron virgo). Where light reaches the river bottom, stones and boulders are covered by grazers such as the gastropods Melanopsis sp. and Theodoxus fluviatilis (Munoz & Prat 1994). Euryhaline species such as the polychaete Ficopotamus and the trichopteran Ecnomus are abundant near the delta (Munoz & Prat 1994). The giant European freshwater pearl mussel (Margaritifera auricularia) present in the lower part of the river has declined dramatically in abundance since the early 20th century (Araujo & Ramos 2000). The introduced zebra mussel, Dreissena polymorpha, was first detected in Ribaroja reservoir in summer 2001, while the helminth Phyllodistomum folium that infects zebra mussels and the Asian bivalve C. fluminea have been recently recorded in the lower Ebro. The fish community of the Ebro is composed of species introduced before 1900 and those introduced after 1900. Most of these fish are vulnerable (such as A. anguilla, P. marinus, C. calderoni and C. paludica), while others are threatened (Aphanius iberus, Valencia hispanica, Gasterosteus gymnurus, Salaria fluviatilis, A. sturio) (CH Ebro 2005). The Ebro catchment encompasses a biogeographic zone where southern and northern fishes occur, making assemblages vulnerable to be introduced and invasive species such as Micropterus salmoides, Sander lucioperca, Gambusia holbrooki, Esox lucius, Ameiurus melas and the large Silurus glanis (CH Ebro 2005). The introduced Asian cyprinid Pseudorasbora parva has recently been recorded in the delta (Caiola & Sostoa 2002). Dam construction also causes an increase in fish density, especially the smaller species.

4.5.6. Management and Conservation The economic use of water for irrigation and reservoir construction is the main environmental disturbance in the Ebro catchment, and has altered the flow regime except in upper tributaries. The Ebro has 187 reservoirs

PART | I Rivers of Europe

impounding 57% of the mean annual runoff. All dams were constructed during the 20th century with 67% of the reservoir capacity built between 1950 and 1975. Three reservoirs have >500 Mm3 in capacity (Ebro, Mequinenza and Canyelles). The Hydrologic Basin Authority (est. 1926) of the Ebro (CH Ebro 2005) was the first organization for managing Spanish rivers. The first objective was to organize irrigation for agriculture. Today, it is responsible for the control of catchment master plans based on the Water Framework Directive. A recent bioassessment indicates ‘good’ and ‘very good’ status of 70– 77% of the examined rivers (CH Ebro 2005). The Spanish National Hydrologic Plan (2001) proposed a water transfer from the lower river (maximum of 1050 Mm3/ year) to the Segura and Jucar in the southeast. The plan also included the construction of 100 new dams and infrastructure for new irrigation areas, as well as for water treatment plants and river channelization. Fortunately the plan was rejected because of environmental concerns (Biswas & Tortajada 2003; Getches 2003). The Ebro headwaters host two National Parks, the National Park of Ordesa and Monte Perdido, and the National Park of Aig€uestortes and Sant Maurici. At the delta, the Natural Park of the Delta de l’Ebre is an important wetland, especially for migrating birds. Apart from these areas, many ZEPAs and LICs (included in Net Natura 2000) occur in the Ebro catchment, mostly in the headwaters (CH Ebro 2005).

4.6. THE TAGUS The Tagus (Tajo in Spanish, Tejo in Portuguese) is one of the largest Iberian rivers, covering a drainage area of 80 600 km2 in Spain (70%) and Portugal (30%). The river runs for 1007 km from east-central Spain in the Sierra de Albarracın (1590 m asl) to the Atlantic Ocean at the estuary at Lisbon, the largest of Europe. It is the longest river on the Iberian Peninsula and third in respect to surface area and discharge. Its name (Tajo = Cut, in Greek) reflects the abrupt fracture that the river forms on the landscape. The main tributaries are the Jarama, Alberche, Tietar, Alagon, Guadelia, Almonte and Salor in Spain, and the Erges, Ponsul, Z^ezere and Sorraia in Portugal (Photo 4.5). The Tagus defines the political border between Spain and Portugal just downstream of Alcantara reservoir. The river flows through Lisbon in Portugal and Toledo and Aranjuez in Spain. The Tagus is navigable for 160 km upstream from its mouth, although several large dams retain water for irrigation and hydroelectric power. The catchment supports the water needs of the largest population (11 million people) in the Iberian Peninsula, including those of two European capitals (Madrid and Lisbon). Some of the Tagus is diverted to the Segura basin, supplying water for another 1.5 million people in southern Spain and supporting the existence of the Tablas de Daimiel ecosystem in the La Mancha Natural Reserve.

Chapter | 4 The Iberian Rivers

PHOTO 4.5 Tagus River at Toledo in 1958 (A) and today (B).

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4.6.1. Historical Perspective Human history in the Tagus originates in the Bronze Age (10th century BC), when inhabitants in the central basin (Spanish and Portuguese Extremadura) engraved stones and erected monoliths along the river, particularly around the city of Caceres. The founding of Lisbon may be related to a Phoenician settlement since recovered objects date from 1200 BC. The Tagus was the central axis of the Roman province of Lusitania in the second-century BC, with the colony of Iulia Augusta Emerita (the present city of Merida) as the capital. During the Arabic domain (11th century), Lisbon was one of the most important cities of Al Andalus with >20 000 Christian, Jewish and Islamic inhabitants.

4.6.2. Biogeographical Setting The creation of the Tagus catchment can be traced back to the late Permian, when an extensive tectonic regime prevailed across the eastern half of the Iberian plate. The Tagus is biogeographically within the Mediterranean region. Mild conditions are expressed by average air temperatures that range from 13 to 17  C with a minimum in the coldest months from 1 to 5  C. The potential vegetation is made up of Q. rotundifolia and Q. ilex, which changes to thickets of Quercus coccifera and Quercus faginea under human pressure.

4.6.3. Physiography, Climate and Land Use The Tagus catchment is delimited by the Iberian Central Range in the north, the Toledo Mountains and Sierra of Montanchez in the south, and the Iberian Mountains (Serranıa de Cuenca and Sierra de Albarracın) in the east. The highest mountains are in the Central Range (2000 m asl), while the Iberian Mountains are <1800 m asl and the Toledo Mountains are <1600 m asl. The river has a relatively steep gradient profile, flowing through deep gorges with waterfalls. Along the Portuguese–Spanish border, the valley side-slopes are steep, but then the river enters into a low hill area and finally onto a flat plain. The Tagus catchment is bordered to the north and west by Precambrian and Palaeozoic mountains of igneous rocks, slates and quartzites, and to the south and east by relatively low lying hills of Mesozoic carbonates. The river runs mainly over schist-greywacke rocks from the pre-Ordovician along the border, although granites are scattered through the areas of Salvaterra do Extremo and Segura. The remaining areas are covered by Tertiary detritic deposits. The Tagus first flows northwest, but later flows west. The tributaries are distributed asymmetrically within the catchment, and the most important (Gallo, Jarama, Guadarrama, Alberche, Tietar and Alagon) enter from the right side. Left tributaries are generally shorter and with less discharge. In Portugal, tributaries originate from the mountains of Serra da Estrela,

PART | I Rivers of Europe

A¸cor and Lous~a. The main tributaries here are the Erges, Ponsul, Ocreza and Z^ezere from the right side, and the Sever and Sorraia from the left side. The Z^ezere and Sorraia together cover 50% of the surface area of the Tagus in Portugal. Mean annual precipitation in the Tagus catchment is 670 mm, and ranges from 500 to 1000 mm. Highest rain fall occurs in the Tietar, Alagon and Arrago basins, where microclimatic conditions allow rich cultures of tobacco, pepper, and apple and cherry trees. Lowest precipitation occurs along the left side of the middle Tagus. In the upper Tagus, winter temperatures are cold and summer temperatures do not exceed 20  C. In the middle and lower catchment, annual mean temperature ranges between 4 and 10  C in the mountains and 14–17  C in the valleys. Precipitation also differs, being 1300 mm and 500 mm, respectively. Nearly 80% of the precipitation falls during the three winter months. The average evapotranspiration ranges from 400 to 720 mm. Steep slopes, as well as hot dry summers, restrict agriculture to near the Portuguese–Spanish border, although other areas are intensively cultured by humans. In the case of the Jarama basin (Vizcaıno et al. 2003), the area occupied by agriculture increased by 5% and industrial use by 26% from 1950 to 1990, whereas riparian forest areas decreased by 31%. In the Sorraia, a system of irrigation channels was built between 1935 and 1965, allowing the transformation of the fertile alluvium to rice plantations.

4.6.4. Geomorphology, Hydrology and Biochemistry The present morphology of the Tagus is a consequence of dam construction throughout the basin. The dams and their regulation have decreased the frequency of high flows and associated sedimentation rates (Martin-Vide et al. 2003). Construction of levees along the river has caused changes in the river channel, especially with respect to riparian vegetation and the formation of sedimentation bars. The floodplain of the Jarama decreased in area from 1750 ha in 1956 to 580 ha in 1999 (Vizcaıno et al. 2003). While meanders and palaeochannels were evident in the floodplain up to the 1950s, there was an obvious reduction by the 1990s because of restrained lateral expansion by the river, as well as a decrease in river width by 50%. The Tagus flow regime shows high seasonality and interannual variability. Discharge is maximal from February to March and minimal in August. The outflow into the Tagus estuary is 315 m3/s, and monthly averages range from 30 to 2050 m3/s. Floods occur mainly in December and January, and can have peak discharges up to 45 times the average. Historical records show a similar pattern in flood distribution (Benito et al. 1998). From 1942 to 1949 and 1971 until today, only two floods exceeded 1500 m3/s, while four surpassed 1000 m3/s. The highest recorded flood was in March 1947, and was estimated between 2500 and 3700 m3/s (Benito et al.

Chapter | 4 The Iberian Rivers

1998; Martin-Vide et al. 2003). Analysis of slackwater deposits suggests that floods of similar magnitude have occurred at least nine times in the past millennia (Benito et al. 1998). The Tagus drains a basin mainly composed of siliceous rocks, as reflected in moderate conductivity values of 650 mS/cm in the upper river and 300 mS/cm downstream of Alcantara reservoir. Major tributaries also have low conductivities (Alberche, 130 mS/cm; Tietar, 135 mS/cm), except for the Jarama at 1300 mS/cm because of heavy industrialization in the catchment. Water conductivity in the Tagus below its confluence with the Jarama is 1800 mS/cm. Mean annual temperature in the main river is 14  C in the upper reach and 18  C downstream of Alcantara reservoir. The Jarama is the most polluted of the main tributaries. This river has high average nutrient concentrations (10.8 mg NO3/L, 12.5 mg NH4/L, 2.18 mg P/L; averaged over the last 10 years). The Alberche (3.86 mg NO3/L, 0.13 mg NH4/L, 0.23 mg P/L) and Tietar (4.04 mg NO3/L, 0.35 mg NH4/L, 0.44 mg P/L) contribute lower levels of nutrients. Around 80% of the basin aquifers show nitrate contamination problems, with the Ocana, Tietar and Alcarria having values >100 mg/L (ITGE 1998). In irrigation channels in the lower Tagus, aquatic macrophytes and algal mats (up to 1 kg fresh mass/m2) are abundant and can cause serious environmental problems (Ferreira et al. 1999). Nutrients have increased significantly in the last 11 years in the middle Tagus. Ammonia is 100 higher in the Toledo (6.41 mg NH4/L) than in the Trillo (0.08 mg NH4/L) and nitrates increase from 3.3 mg NO3/L in the Trillo to 15 mg NO3/L in the Toledo. Mining activities are important in the catchment. Lithic industries are common in the main valley and northern tributaries. Major deposits of sepiolite are found in the Tajo basin and actively mined. Total chromium concentrations in the Jarama (mainly in its hexavalent form) reach 0.05–0.10 mg/L. Levels of this metal in sediments (9–5128 mg/kg DW) and interstitial waters (0.03– 0.75 mg/L) are high as well (Arauzo et al. 2003). The river between the Jarama and Tagus rivers to the Toledo is the most polluted, also from chemicals such as anionic surfactants and arsenic. At the Tagus estuary, there is a large input of industrial pollutants. Arsenic emissions from industrial complexes have been estimated at 1000– 2000 tons/year (Andreae et al. 1983).

4.6.5. Aquatic and Riparian Biodiversity The irrigation channels in the lower Tagus and Sorraia create conditions for algal proliferation. Filamentous algae are common, dominated by Cladophora glomerata and diatoms such as Fragilaria construens, Achnanthes subhudsoni and Navicula goeppertiana. Macrophytes in slow-water areas include Digitaria sanguinalis, Echinochloa crus-galli and Cyperus diformis. Degraded, nutrient rich areas are typically invaded by giant reed, reeds and cattails. Riparian areas

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along the Tagus are frequently vegetated by willows, white poplar, and elms. In torrential reaches subject to summer low water, tamarix (T. africana) and rose bays (Nerium oleander) are common. Large gray willows were quite common in the lower Tagus, their disappearance being related to rice cultivation. Exotic invaders (Eichhornia crassipes, Myriophyllum aquaticum) show high local densities and may outcompete the native Potamogeton crispus, Ceratophyllum demerson and M. spicatum (Ferreira & Moreira 1999). Small streams in the flat-lands of the southern Tagus are inhabited by mayflies of the genera Baetis, Caenis, Paraleptophlebia, and Ephemerella, stoneflies such as Isoperla, and the Coleoptera Oulimnius. In the north at Serra da Malcata, small streams have a higher diversity of macroinvertebrates than streams in the south. Taxa include caddiflies such as Atripsodes (Lepidostomatidae) and Tinodes (Pychomyiidae), dragonflies (Chalcolestes), Notonectidae (Notonecta), coleopterans (Oulimnius, Helophorus, Laccobius, Anacaena, Dytiscus), stoneflies and mayflies (Caenis, Choroterpes, Cloeon), and common dipterans (Chironomidae, Tipula) (INAG, unpublished data). Among the introduced invertebrates, four species are relevant in terms of biomass, numbers, potential impact or their geographic distribution: the freshwater asiatic clam C. fluminea, the Chinese mitten crab Eriocheir sinensis, the Louisiana red crayfish P. clarkii, and the snail Potamopyrgus jenkinsi. M. auricularia was once abundant in the Tagus basin (Araujo & Ramos 2000). The rice fields are important habitats for a large variety of invertebrates including P. clarkii, Gastropods, Oligochaetes, Daphnia, Siphlonurus, Lestidae, Gerridae, Anisops, Dytiscidae, Hydrophilidae, Coelostoma, Tipulidae, Culicidae and Chironomidae. The Tagus catchment is transitional between the north containing some central European fishes and the south inhabited by endemic species. It forms the southern limit for B. bocagei, Rutilus arcasii, Leuciscus carolitertii and C. calderoni, and the northern limit for Barbus comizo, B. microcephalus and Rutilus lemmingii. The subspecies of C. polylepis also have their distribution limits in the Tagus basin (Doadrio et al. 1991). Today, three native Iberian Peninsula fish (B. bocagei, C. polylepis and L. pyrenaicus) can be found in the Tagus basin, in particular in the rivers Ambroz, Guadiela, Jarama, Lozoya, Sorbe, Tajuna and upper Tagus (Martınez Capel & Gracıa de Jalon 1999). In Portugal, native fishes include the barbel Barbus comiza, the endemic cyprinid Chondrostoma lusitanicum, and the endemic R. macrolepidotus and R. alburnoides. Good populations of brown trout (Salmo truta fario) can be found in the headwaters of some tributaries (Mayo-Rustarazo et al. 1995). Carmona et al. (1999) highlighted the distinctive fish community in the Alagon River, where the local endemic Cobitis vettonica is found. C. polylepis, B. bocagei and Tropidophoxinellus alburnoides have a wide distribution throughout the lower Tagus. C. paludica, L. pyrenaicus and R. lemmingii usually prefer lowland reaches with slow currents. Non-native fish species in the Manzanares comprise 80% of the fish

136

community (Morillo Gonzalez del Tanago et al. 1999). Migratory fish species (such as P. marinus and Lampreta fluviatilis) can only move upriver until Alcantara dam. At least six species of amphibians and reptiles inhabit the Tagus estuary, including the Iberian or Portuguese Painted Frog (D. galganoi), the Common Tree Frog (Hyla arborea), the Mediterranean Pond Turtle (Mauremys leprosa) and the Iberian Spadefoot Toad (Pelobates cultripes). The geomorphology of the upper Tagus provides habitats for several birds of prey (Aquila chrysaetos, Neoprhon percnopterus, Hieraetus fasciatus, Bubo bubo and Gyps fulvus). The Tagus wetlands are highly important for wintering populations of avocet, black-tailed godwit, redshank, grey plover, shoveler and lesser black-backed gull (Moreira 1999). Other species that appear seasonally in the estuary are Egretta garzetta, Charadrius alexandrinus, Charadrius hiaticula, Calidris alba, Limosa limosa, Arenaria interpres, Anas crecca, Anas lypeata, Recurvirostra avosetta, Limosa lapponica, Numenius arquata, Tringa totanus, Larus ridibundus, Larus fuscus, Pluvialis squatarola, Calidris canutus, Calidris alpine, and Anas platyrhynchos (Moreira 1999). Migratory birds and birds of prey use the Natural Park of Tejo International as refuge and for nesting, including the Egyptian vulture, Short-toed eagle, Bonelli’s eagle and the Black stork. In the alluvial sediments and fluvial islands in the middle river are found Circus aeruginosus, Ciconia nigra, Falco peregrinus and numerous limnetic birds like Nycticorax nycticorax, Egretta garzetta and Bubulcus ibis. In the Natural Park of Tejo International, some protected species are found, including the otter, the small spotted Genet, the wild cat, elk, and the Egyptian mongoose. Water moles are present in pollution-free mountain streams. The Eurasian otter and the European polecat have been recorded in the estuary.

4.6.6. Management and Conservation Management of the Tagus catchment is strongly influenced by water needs for irrigation. The total irrigated land increased from 9340 to 230 720 ha since 1940. Reservoir capacity in the upper and middle Tagus is 12 000 Mm3 and in the overall catchment is 14 500 Mm3, corresponding to 74% of the average annual runoff. River flow is strongly regulated. The Tagus is also used to transfer water from the Entrepenas-Buendıa reservoir in central Spain to the Segura basin (so-called Tagus-Segura Transfer), being in operation since 1979 to meet the needs for human consumption and irrigation in the Segura basin. Part of the flow (<5%) is redirected to the Guadiana basin for the maintenance of the Natural Reserve of Tablas de Daimiel. The Tagus–Segura Transfer has caused severe impacts in both river basins. The UNEP (2003) report indicates that the water demand in the catchment has doubled in the last 24 years to 500 Mm3 because of irrigation and tourism. Water no longer flows in some places in summer, and the legal minimum flow of 6.0 m3/s is sometimes not enforced.

PART | I Rivers of Europe

The Natural reserve of the upper Tagus comprises the headwaters of the Tagus and the main tributaries of Hoz Seca, Tajuelo, Cabrillas, Gallo, Bullones, Arandilla and Ablanquejo. There are two fluvial karstic systems in the south, The Barranco of the Dulce River and the Salado river valley. The Henares River has an excellent riparian forest and special geomorphology. Several reaches with Atlantic riparian forest are proposed as LICs on the Canamares, the Tajuna, Valfermoso de Tajuna and Brihuega rivers. Other important riparian areas considered as LICs are along the Alberche and middle Tagus (Tagus in Castrejon, Barrancas of Talavera). The Tagus estuary encompasses 18.2 km2 of marshland covered with halophytic vegetation and is periodically flooded with saline water. In the upper estuary, the saltmarshes have been a Nature reserve since 1976 (Reserva Natural do Estuario do Tejo). In the lower Tagus, the marsh ‘Paul do Boquilobo’ is a Biosphere reserve. The Tagus basin is managed by the Hydrologic Basin Authority of the Tagus (CHT) in Spain and by the National Institute for Water (INAG) in Portugal. Preliminary studies had to be completed by December 2004 by each river basin district, including the identification, delimitation and characterisation of water bodies, research into the anthropogenic pressures, and the selection of potential reference sites. A large study on the biological and chemical quality of the river, classified 30% of the catchment as being in a very good ecological state, and 30% to be strongly polluted (Moreira et al. 2002). The environmental problems are mainly related to industry in the estuary, the presence of dams, river abstraction for irrigation, and levees. As a consequence, riparian areas have decreased nearly 52% in the Tagus basin and 88% in the Jarama due to changes in land use (mainly agricultural activities in the floodplain) and changes in the hydrological regime (Molina Holgado 2002). Several reservoirs are eutrophic, and some even hyper-eutrophic (Pena-Martınez & Serrano-Perez 1994; Bai~ao & Boavida 2005).

4.7. ADDITIONAL RIVERS €era 4.7.1. The Agu The Ag€uera drains 145 km2 in the Cantabric region in north Spain, between the Basque Country and Cantabria. It has a typical Atlantic-influenced flow regime (Atlantic ecoregion) with a humid oceanic climate and high discharge relative to its size. Most streams like the Ag€uera also have high gradients. The Ag€uera is one of the most natural rivers in the region and one of the best studied in the Iberian Peninsula, especially from a functional viewpoint. The Ag€uera flows through Cretaceous materials, especially sandstones. Limestones dominate its middle catchment and the infiltration water here forms springs and diffuse groundwater sources to surface waters. The Ag€uera receives 1500 mm precipitation annually, and rains are regularly distributed throughout

Chapter | 4 The Iberian Rivers

the year. The average annual temperature is 14.3  C, ranging from 9.8  C in January to 18.5  C in August (Photo 4.6). There is a low human density in the catchment with larger villages having 2000 people, although the coastal area is becoming increasingly populated in recent years. Primary activities in the catchment include forestry, livestock and agriculture. Nearly 50% of the catchment is covered by tree plantations, in particular Eucalyptus globulus and Pinus radiata, especially in the lower basin. The remaining landscape is occupied by meadows and grasslands, and 17% by native oak and evergreen oak forests. Interesting saltmarshes and sand dunes form at the mouth of the Ag€ uera. This basin was formed by Pyrenean orogeny that caused several foldings and faults, and the north-northwest flow of the main channel. The river originates at 450 m asl and is 30 km long. Channels are mostly straight and incised, and disconnected from the floodplains. The annual average discharge of the Ag€uera ranges between 2 and 4.5 m3/s at the mouth, and interannual variability is low. The steep gradient causes torrential flows at any time in response to rains. The Ag€ uera has relatively clear, moderately mineralised waters. The longitudinal variability of its chemistry reflects the local geology as well as land use and sewage inputs. The upper river is low in mineralization, which later increases in the middle reach because of calcareous geology, especially during low flows. Nutrient content increases with the increase in conductivity. Nitrate values are moderate, rarely

PHOTO 4.6 Ag€ uera River in its middle section (Photo: Sergi Sabater).

137

exceeding 1.2 mg/L, and decrease in the middle and lower sections under low flows. Phosphates are low in the headwaters and middle sections of the river, except downstream of villages. In the lower river, nutrients increase because of the influence of towns and lack of water treatment plants. This situation has improved somewhat in the last few years. Oxygen levels can be low in tributaries receiving dairy sewage, and phosphorus concentrations are 10-fold higher than in the main river (Elosegui et al. 1995). Algal biomass is low in the Ag€uera headwaters, being dominated by diatom assemblages. Downstream, when the shade is reduced, filamentous algal communities dominated by Cladophora are abundant. Algal biomass is higher during stable flow periods, although light availability limits biomass in shaded reaches of the river (Elosegi et al. 2006). Macrophytes other than mosses or liverworths are rare in the Ag€uera. Riparian forests are generally present and in a good state along the Ag€uera, and consist of mixed forests of alder, ash and oak, as well as plantations of London pine. In moist areas, rare ferns like Woodwardia radicans or Trichomanes speciosum can be found. Macroinvertebrates are diverse in the middle and lower reaches of the Ag€uera, dominated by collectors and generalist invertebrates (Riano et al. 1993). The most abundant groups are Oligochaeta, mayflies, chironomids and elmid beetles. Filterers (Simuliidae and Hydropsychidae) occur below pollution inputs, and shredders (Echinogammarus

138

and several stoneflies) are abundant in the forested headwaters. Shredders make up >25% of the macroinvertebrate biomass in the headwaters. The life cycle of most shredders is asynchronised with the period of leaf fall (Basaguren et al. 1996). Nutrient pollution based on the BMWP bioassessment index seems to have little effect on the macroinvertebrate community, except for some areas in the middle and lower river. Fish communities are relatively diverse, although densities seem to have decreased during the last few years. Brown trout (S. trutta) and minnow (Phoxinus phoxinus) are the main species found along most of the river. Salmon (Salmo salar) reproduces in some sections, and Chondrostoma toxostoma is found in slow waters. The metabolism and functioning of the river is tightly related with the dynamics of organic matter entering and decomposing in the system (Elosegi et al. 2006). The replacement of native forest by eucalyptus plantations has reduced nutrient levels, increased inputs of oils and phenolics, and changed the timing of leaf fall (being more evenly distributed during the year). These changes certainly influence the macroinvertebrate fauna, although the high retention of organic matter in the Ag€ uera may reduce the effect on consumers (Pozo et al. 1997). The Ag€ uera has a large volume of large woody debris (Diez et al. 2000). Extensive knowledge of the river made possible to detect the effects of drought as well as that of severe clear-cuts in the basin. Water quality is an issue below the two largest villages (Trucios and Guriezo) as well as in some small tributaries. Promising is that some wastewater treatment plants will begin operating in the near future and should improve the nutrient situation and assist the self-purification capacity of the stream (Elosegui et al. 1995). Intensive forestry operations on eucalyptus plantations are a serious problem in the catchment. Parts of the headwaters, middle and lower sections are Natura 2000 sites, and part of the catchment also will be included in the Natural Park of Armanon, to be created in 2007.

car 4.7.2. The Ju The J ucar catchment is in the eastern Iberian Peninsula and ucar has nine major covers an area of 21 208 km2. The J tributaries (Cenia, Mijares, Palancia, T uria, J ucar, Serpis, Marina Alta, Marina Baja and Vinalopo). The basin has a diverse and irregular hydrology, common to most Mediterranean rivers. The J ucar is densely populated (4.4 million inhabitants in 2001), plus 1.5 million in tourists. The hydrological resources of the J ucar are estimated at 3400 Mm3/year and the total water demand of the basin is 3650 Mm3/year, mostly for agricultural use, creating a large water deficit. Agricultural water demand is high because 22% of the 1.8 million ha of agricultural land is irrigated (Photo 4.7). Geographic differences cause climatic irregularities between the north and south, and the east and west regions of the basin. The average annual rainfall is 500 mm, ranging

PART | I Rivers of Europe

from 250 mm in the south to 900 mm in the north. The headwaters have the lowest mean temperatures and the highest precipitation in the basin (Una: 5  C, 929 mm). In the La Mancha plain (southwest), mean annual temperature is 15  C, but differences between minimum and maximum temperatures can approach 20  C due to the Mediterranean continental climate. The Jucar discharge shows high seasonality (maximum in autumn and winter, and minimum in summer) and interannual variability. In littoral areas, rainfall is dominated by humid easterly winds that can lead to local intense rains at the end of summer. The climate causes frequent floods at the end of summer and autumn, although these are mostly attenuated by reservoirs. In October 1982, a flash flood caused the breach of Tous dam in the lower Jucar that claimed 12 casualties. Average river discharge at El Picazo (1952–2006; CHJ) is 82.7 Mm3, ranging from a maximum of 295 Mm3 and minimum of 12 Mm3. Discharge has decreased between the period 1952–1983 (100 Mm3) and the period 1984–2006 (58 Mm3). The intensive use of water has resulted in deep morphological alterations in the catchment. A total of 43 reservoirs are presently found in the basin, used mainly for irrigation and energy generation. Of these, 18 are on the Jucar, 11 on the Mijares, and 4 on the Turia. Small dams for irrigation are also distributed along the drainage network. Mean water temperature in the middle and lower river is 16.2  C (ranging from 7.2 to 24.6  C), and conductivity is 800 mS/cm. The mean ammonia concentration is 0.07 mg/ L (maximum = 0.36 mg/L) and nitrate reaches 10 mg/L. Total phosphorus concentration is 0.07 mg/L with maximum values of 0.64 mg/L. A total of 128 species of macrophytes, 266 species of diatoms and 390 species of macroinvertebrates were listed for the Jucar catchment. Notably, the endemic crustacean Dugastella valentine is found in the natural reserve of Pego-Oliva. The macroinvertebrate comunity indicates that reaches with good ecological status are mostly in the high altitudes, while those at middles altitudes (800–200 m asl) are regulated but have good or acceptable ecological quality. Reaches in the lowlands (<200 m asl) have poor or bad quality (Martınez Mas et al. 2004). The Jucar basin has a diverse fish community. Trout (S. trutta) is common in the headwaters and Barbus and L. pyrenaicus in the middle and lower reaches. The presence of non-native species is low in the headwaters of the J ucar, Turia and Mijares, but in the middle and lower reaches there is a higher presence of cyprinids. Blennies (S. fluviatilis) have been observed in the Jucar as well as in the tributaries Cabriel and Escalona, and in several irrigation channels (Hernandez et al. 2000). V. hispanica and A. iberus are two endemic fishes found in fresh and brackish water areas, as well as in channels and ponds along the littoral. These species have disappeared from the main lagoons due to G. holbrooki that was introduced in the Albufera 80 years ago to fight paludism. It uses the same habitats as A. ibericus and V. hispanica (Soria 2006).

Chapter | 4 The Iberian Rivers

139

PHOTO 4.7 J ucar River at Alcala de Jucar (Photo: Sergi Sabater).

There are numerous valuable wetlands with protective status in the catchment, and four of these are included under the RAMSAR agreement. The L’Albufera de Valencia is a natural park that includes the coastal line between the Turia River and Cullera Mountains, the Albufera lake, and the rice fields around the lake up to the Jucar River. Salinity of the Albufera lake is near 2 g/L. The lake area is visited by >250 species of birds and some 90 of these nest in the area. The other three RAMSAR sites are the Prat de Cabanes-Torreblanca, the Marjal de Pego-Oliva, and the Santa Pola Saline. Besides these, another 48 wetlands have been inventoried in the basin (Nebot 1997). Proposed protected areas include the Hoces del Cabriel and Hoces of the J ucar. The Jucar River basin was selected as The Pilot River Basin of the WFD in Spain in 2002 as part of the European Water Framework Directive as managed by the Jucar Water Authority (CH J ucar 2000).

4.7.3. The Mondego The Mondego is entirely in Portugal with a total length of 237 km and drainage area of 6670 km2. It originates at Serra da Estrela, the highest mountain range in Portugal. The river is traditionally divided into three sections. The upper Mondego is 31 km long with a mean slope of 2.5%

and lies partly within a glacial valley. The middle sector is the largest at 168 km with a slope of 0.4–0.1%. This sector is constrained by a steep and closed valley. The final sector of 38 km flows from the city of Coimbra where a narrow valley opens to a wide alluvial plain with low slope (0.05%). Here, it flows over Meso-Cenozoic limestone. The Mondego lies in a transition area of Atlantic and Mediterranean climate with an average basin temperature of 13  C and annual precipitation of 1130 mm, 70% of which occurs from October to March. Nearly half a million people currently live in the Mondego catchment. Agricultural activities are intense in the lower Mondego valley, whereas wood extraction for pulp production is important in the remaining basin (Photo 4.8). Mean annual discharge of the Mondego is 88 m3/s, and the flow is highly seasonal and rainfall dominated. Measured runoff at Coimbra before construction of Aguieira dam ranged from 1 to 3000 m3/s (Pardal et al. 2002). Highland tributaries are acidic (pH values occasionally <5) and poorly mineralised (conductivity <50 mS/cm, alkalinity <20 mg/L). In the lower section, the geology typically causes water pH >7, conductivity >200 mS/cm and alkalinity >100 mg/L (Feio 2004). There are 25 reservoirs along the Mondego and its main tributaries that are used for energy production and irrigation purposes. The Aguieira is the main reservoir producing electricity and regulating flows. Before reservoir construction, in particular the Aguieira, Raiva and Ponte-A¸cude, the river

140

PART | I Rivers of Europe

PHOTO 4.8 Mondego at Serra de Estrela (Photo: Manuel Gra¸ca).

transported large amounts of sediments that even elevated the riverbed. A total of 388 taxa of phytoplankton were recorded in the basin, 232 of them being diatoms (Santos et al. 2002). Aquatic plants include the curly pondweed, the pond water-crowfoot, the pond water-starwort, water milfoils and the introduced parrot feather. Widely spread riparian trees include ash, black-poplar, willows and alder. Over 200 invertebrate taxa were cited in recent studies of the river (Feio 2004). Due to low pH, crustaceans and gastropods are rare in the upper basin, whereas stoneflies (e.g. Leuctra sp., Nemoura sp., Perla sp.) and caddisflies (e.g. Sericostoma sp., Hydropsyche spp., Lepidostoma hirtum, and Rhyacophila spp.) are common. In the middle and low sections, these species are replaced by mayflies (Habroflebia, Habroleptoides, Ephmerella sp. Serratella sp., Caenis sp.), other caddisflies (Chimarra marginata, Cheumatopsyche lepida, Lype auripilis) and some gastropods (e.g. Ancylus fluviatilis, Potamopyrgus spp., Physa sp. and Lymnae sp.) (Gra¸ca et al. 2004, Feio 2004). In the lowlands, the shrimp Athyaephyra desmarestii and the introduced Louisiana crayfish P. clarkii are widespread. A total of 19 fish species were identified in the basin (Pardal et al. 2002). Taxon richness is highest in the lower section. Important native species include the ruivaco (R. macrolepidotus), escalo (L. carolitertii), Iberian barbel (B. bocagei) and Iberian nase (C. polylepis). Common intro-

duced fish include the goldfish, carp, gudgeon, rainbow trout and mosquito fish. The Mondego is one of the most important rivers in Portugal for four commercially important diadromous fish, the sea lampre, allids shad, twaite shad, and eel. Sixteen species of amphibians are found in the basin, with high densities in the lowland section because of the freshwater marshes. One distinctive species is the goldstriped salamander (C. lusitanica). Two aquatic reptiles occur in the Modengo basin, the water lizard Lacerta scheibreri and the freshwater tortoise M. leprosa. Nearly 70% of the Mondego basin is classified as being in good biological and chemical condition. Critical conditions are only found in the lowland section (Moreira et al. 2002). The lower Mondego has been straightened and the banks reinforced for flood control. Due to agricultural activities, the area is heavily impacted from runoff of nutrients and pesticides, which end up in the estuary. The connectivity between the river and its floodplain was lost because of bank reinforcements that facilitated plant invasions in the lower Mondego. Today, nearly 10% of the recorded 212 riparian species are invasive species (Aguiar et al. 2001), and the dominant taxa are exotic. Other environmental problems include the invasion of the lower Mondego by the Louisina red crayfish. The 25 reservoirs along the river also block fish migration (mainly eels and lampreys). Lastly, large-scale Eucalyptus plantations have been associated with a lower diversity of aquatic hyphomycetes in some streams (Gra¸ca et al. 2002).

Chapter | 4 The Iberian Rivers

The Mondego catchment contains a wide variety of habitats for birds, particularly in the marshlands and estuary, where 137 species have been recorded. Many of these are winter visitors, including the wader (Dulin calidris), the lundin (Calidris alpina), and the avocet (Recurvirostra avoseta). Summer visitors include the black-winged stilt (Himantopus himantopus) and kentish plover (C. alexandrinus). Aquatic mammals in the river are represented by two main species: the otter (Lutra lutra) and the water mole (Galemys pyrenaicus).

4.7.4. The Segura The Segura basin is in the southeast Iberian Peninsula, covering an area of 19182km2. The Segura is 325 km long. The romans called the river Thader and the arabians WarAlabiat, which means ‘white river’. The term ‘white’ might be due to the presence of carbonate and sulfate deposits in some areas from gypsum marls and the arid and semi-arid conditions of the basin. The river originates in the Segura Mountains (1413 m asl) near the Guadalquivir source. The river flows from the Bethic Mountains to the east and into the Mediterranean Sea. The basin is delimited by the Bethic Mountains to the north and west (separating the Guadalquivir basin), the Prelitoral Murcian range to the southwest, and the Carche range to the east. The Segura is separated from the J ucar basin in the north by the Pinilla and Alcaraz ranges (Photo 4.2). The Segura is in the most arid zone of the Iberian Peninsula. Rainfall is irregularly distributed in the year and large floods can occur that affect human settlements throughout the drainage. In spite of this, a diversity of climates and hydrologies are found within the basin, being related to the basins diverse geography. Most of its water is collected in the upper river in the Segura, Mundo and, later on, the Guadalentın River. The middle reach has an arid landscape, with highlands and dry hills. A few green ‘oases’ make up the riparian zone along the river channels. The most important tributaries with permanent flow are the Madera, Tus and Mundo from the left side and the Zumeta, Taibilla and Guadalentın flowing from the right. Agriculture in basin is based on an irrigation system that has greatly altered surface flows. The Romans had already developed the Murcia’s orchard, still one of the most productive areas on the Iberian Peninsula. Orihuela was an important city during the Muslim occupation of the basin. Most people live in cities (such as Cartagena and Lorca) with <50 000 inhabitants. The largest city is Murcia with nearly 400 000 people. The basin has a large number of reservoirs that strongly regulate the flow of the river. High water demand has also resulted in overexploitation of subterranean aquifers in some areas. Today, land use in the basin is mainly agriculture (52%), the remaining landscape comprising forest or seminatural areas (42%) and urbanized areas 2.1% (CH Segura 2005). Agriculture is mostly developed in the

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main valleys of the Segura, Guadalentın and Campo de Cartagena. The Segura basin is within the Mediterranean climatic region. There is evidence that the basin was a refuge for thermophilous plants during the last glacial period (Carrion et al. 2003). Vegetation is sparse in many areas of the Segura river basin today. In the Chıcamo catchment, the vegetation is degraded and includes mostly slow-growing shrubs of Stipa tenaccissima, Thymus hyemalis and Rosmarinus officinalis. The vegetation in the Guadalentın valley is Mediterranean xerophytic scrub plants associated with limestone (Pistacia lentiscus, Olea sylvestris). Bedrock in the lower basin is composed of limestones and marls of Triassic to Cretaceous age, while the sedimentary alluvium comprises materials from the Upper Miocene to contemporary materials (conglomerates, sandstones, marls and gypsums). During the lower Pliocene, the Bajo Segura fault underwent significant activity that raised the southern part of the basin. Since then, sedimentation has been continental (alluvial and fluvial) except in the east where there is a transition to marine deposits. The complex geology of the catchment is responsible for a complex aquifer system that maintains flowing water in the river. In central areas of the basin, soils are poorly developed and highly erodible (Martınez-Mena et al. 1998). The basin exhibits high seasonality in climate with frequent drought, intensive rainfall and floods, periods of high temperatures and periods with low temperatures. Mountains (Segura, Alcaraz, Taibilla) in the upper catchment are oriented northwest to southeast, intercepting the Atlantic fronts from the west that causes rainfall to drastically diminish from northwest to southeast. Precipitation near the coast is <300 mm/year. Temperature ranges from 10  C in the Segura range to 18  C near the coast. The lowest temperatures occur in December and February, while the highest occur in July and August. In summer, winds from North Africa are common and can increase temperatures to 40– 45  C. In contrast, dry polar winds produce low temperatures and freezing conditions. Potential evapotranspiration increases from 600 to 700 mm in the upper basin to 950 mm in the middle and lower areas and 850 mm on the coast (at Mar Menor). The water deficit is high in the middle and lower reaches of the Segura, where demands are twice the resources available. The Segura captures most of water it transports from the upper catchment (Segura and Mundo Rivers). The river has a nivopluvial regime in the upper catchment and a Mediterranean fluvial regime downstream with major floods in autumn. Downstream, mainly intermittent tributaries, called ramblas, of low discharge and torrential regime enter the river. For example, the Chıcamo River drains a watershed of 502 km2 and is 60 km long, but it has stretches of flowing water separated by several discontinuous reaches in which surface flow is restricted to rainy periods. The Rambla del Moro is a more extreme intermittent tributary of the Segura, as 90% of the drainage network carries water only after

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heavy rainfall. Ramblas in southeast Spain include habitats with high biodiversity and various endemic species that are vulnerable to a range of human impacts (Gomez et al. 2005). Rain intensity in the basin causes the flow to be mostly Horton runoff, resulting in the formation of gully channels (Vandekerckhove et al. 2000). Salinity and conductivity in the Segura are among the highest of Iberian rivers. High values (ranging from 1 to 10 mS/cm; Toro et al. 2002) are due to the high solubility of the marl substrate as well as to high evaporation and low precipitation. The large variation in discharge is responsible for seasonal variation in water salinity and nutrient content. Conductivity and oxygen also show major changes from the headwaters to the mouth. For instance, the mean conductivity of the Segura is 400 mS/cm at the city Elche, while at Orihuela it reaches 2634 mS/cm (25 year record). In the headwaters, nutrients average 1.2 mg/L nitrate, 0.12 mg/L ammonium and 0.02 mg/L phosphate, whereas values increase to 2.5 mg/L nitrate, 2.5 mg/L ammonium and 0.64 mg/L phosphate downstream at Orihuela. The Mundo River has the lowest nutrient content in the catchment. Suspended solids are typically 100 mg/L with peaks from floods reaching 4400 mg/L (Elche) to 14 000 mg/L (Orihuela). High salinity and nitrates are related to the nitrogen-rich content of the sedimentary marl substratum (Vidal-Abarca et al. 2000). In ramblas, a marked increase in nutrient content (nitrate and phosphate), alkalinity and suspended solids occur after floods, while conductivity decreases due to the dilution effect of high discharge (Ortega et al. 1988). Aquatic and riparian biodiversity in the Segura is related to the different flow regimes in the different rivers and streams in the catchment. Salix sp., Populus sp. and U. minor are the most representative species in permanent waterbodies, and Tamarix sp. and N. oleander may also occur. The most abundant macrophytes in permanent waters are Typha domingensis, Phragmites australis and Juncus sp. Along most rivers on the left side, shrubs are the natural vegetation and much land is dedicated to citrus and horticultural crops. Riparian vegetation is sparse because of frequent floods, with pockets of P. australis, T. canariensis and Juncus maritimus being found. Primary production and respiration in the Segura is high due to its aridity and extreme Mediterranean character (Suarez & Vidal-Abarca 2000, Velasco et al. 2003). Aquatic primary producers found in the Chıcamo include the macrophyte Chara vulgaris (mean annual biomass of 25 gC/m2) and diatoms on fine sediments (Nitzschia, Amphora, Navicula, Gyrosigma and Pleurosigma; mean annual biomass of 5 gC/m2). In comparison with other Mediterranean rivers, the Segura shows a strong gradient in salinity and temperature that can be selective for certain groups of macroinvertebrates such as Plecoptera, Ephemeroptera and Trichoptera. Invertebrate assemblages show adaptations to the fluctuating flow regime of ramblas (high floods, drought). Life cycles of macroinvertebrate are adapted to temporary waters (high P/B ratios, multivoltine life cycles and asynchronous recruit-

PART | I Rivers of Europe

ment) (Peran et al. 1999). The macroinvertebrate community of the upper Segura affected by regulation has a lower diversity than in the unregulated Mundo (Torralva et al. 1996). In the upper Segura and Mundo, salmonids, especially trout, are the main fish. Native salmonids are currently being replaced by introduced rainbow trout. Barbus sclateri is an abundant endemic fish in the mid-southern Iberian Peninsula, including the Guadiana, Guadalquivir and Segura Rivers (Elvira 1995, Doadrio 2001). Fishes in the middle reach of the Segura are characterized by the barbel, coexisting with C. polylepis, G. gobio, S. pyrenaicus and Oncorhynchus mykiss (Oliva-Paterna et al. 2003). Streams with intermittent flows have the lowest fish condition values, while sites with permanent flow have the highest (Oliva-Paterna et al. 2003). The Natural Park of Sierra del Segura, Cazorla y Las Villas (Biosphere Reserve) lies in the headwaters, and the Spanish Ibex Capra pyrenaica is found here. Sensitive areas to nitrate contamination are Laguna del Hondo, Salinas de la Mata, Salinas de Torrevieja, and Mar Menor. The Hydrologic Basin Authority of the Segura (CHS) is responsible for the water management of the catchment and has developed a hydrology plan for the basin. The needs and uses of water was a primary objective in the hydrologic plan due to water scarcity in the region.

4.7.5. The Ter The Ter drains about 3010 km2 in northeastern Spain. Its headwaters are at 2500 m asl in the Pyrenees and it flows 208 km to its mouth in the Mediterranean Sea. The main tributary in the upper catchment is the 30 km long Freser River. In the middle reach, the Ter receives small tributaries such as the Gurri and Major. In this reach are three reservoirs (Sau, Susqueda and El Pasteral; total capacity of 402 Mm3) that strongly influence flow and water quality in the lower river. In the lower river, the main tributary is the Onyar with a Mediterranean flow regime. Here is located Lake Banyoles, a mid-altitude lake and one of the largest in Spain. It has a karstic origin and is fed mainly by groundwater. The Ter is a 5th order river at its mouth. Headwaters and some tributaries in the upper catchment flow over granite and slate, while others drain areas rich in gypsum. The middle and lower river, including many tributaries, drain calcareous and marl areas. Climate differs between the headwaters and the middle and lower parts of the catchment. Headwaters have an alpine influence with cold winters and mild summers, and annual rains ranging from 1000 to 1500 mm. In upland sub-basins, the climate is milder but with abundant rain. In the lowlands and near the mouth, the climate is Mediterranean, with dry summers and mild winters and a rainfall between 700 and 800 mm (Sabater et al. 1995). The Ter basin is strongly influenced by human activity. The first human settlements date from 120 000 to 90 000 years BC, but the first important changes began in the Middle

Chapter | 4 The Iberian Rivers

Ages with the development of wool mills and iron forges that caused major deforestation over large areas. With the Industrial Revolution in the 19th century, human activity and transformation of the river catchment progressively increased. Along the river are a large number of small dams and bypass channels for the generation of water power that has prevailed until today. Regulation of the river was complete by the 1950s with the construction of three large reservoirs in the middle reach. This reservoir system is used for hydroelectric production and water supply for the city of Barcelona and surroundings (700 million litres per day). Agricultural and farming activities are common in the basin. While higher rainfall makes irrigation unnecessary in the upper basin, irrigation is common in the middle and lower parts and is controlled by a series of channels. Farming has caused pollution of both surface and ground waters. Presently, the Ter has only some 1st and 2nd order tributaries that remain undisturbed, whereas the remaining network has been subject to intensive and extensive human pressure that significantly reduced the quality and quantity of the river and riparian habitats. Flow patterns differ between the upper and lower sections of the river. The headwaters have a nivopluvial regime with low flows in winter and higher discharge in spring from snow melt. In the middle and lower parts of the river, discharge is mainly determined by rainfall but regulated by the reservoirs. In these sections, the flow regime is Mediterranean. Flow increases after autumn rains often result in floods. Precipitation is scarce in summer and discharge can decrease substantially in the lower Ter. The average annual discharge of the Ter is 840 Mm3, but there is large interannual variation. Annual water flows from 1955 to 1988 (Armengol et al. 1991b) show two periods of maximum water flow in May (28.6 Mm3) and November (17.6 Mm3); and two minima in August (11.4 Mm3) and February (14.2 Mm3). Water chemistry of the Ter is influenced by the complexity of the catchment and the variability in discharge. In the headwaters, the bedrock is siliceous and the human density is low. Here the concentration of dissolved solids (TDS) are <20 mg/L. Upstream of the reservoirs, the TDS concentration is 50 mg/L and is even higher in polluted tributaries (>50 mg/L in the Gurri). The reservoirs cause a reduction downstream with TDS at 20 mg/L (2000–2005; ACA data base). The chemistry of the Ter waters shows a continuous downstream trend from highly bicarbonate-dominated to chloride-dominated waters (Sabater et al. 1995). Conductivity increases from <100 mS/cm in the headwaters to 600 mS/cm in the lower river (2000–2005; ACA data base), being related to the increase of rock weathering and to higher human activity in the middle and lower river. Nutrient concentrations are related to land use activities and hydrology. The influence of lithology on water chemistry is significant only in the headwaters, while factors related to human activities are more important downstream (Sabater et al. 1990). The N:P ratio (N as dissolved inorganic nitrogen

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and P as reactive soluble phosphorus) is high in the headwaters but decreases downstream, in particular during summer. Values of N:P <30 occur in areas influenced by human activities. Phosphorus inputs from the river (at Roda de Ter) into Sau reservoir increased from 1968 to 1992 due to the increase of industrial and human activities in the basin (Armengol et al. 1999). This pattern shifted during the 1990s because of the completion of wastewater treatment plants. Dissolved inorganic nitrogen (DIN; mainly ammonium) behaved quite differently during that period until the treatment plants began biological treatment. Diatoms are the most widespread algae in the river (Sabater et al. 1995). Siliceous headwaters are characterized by Hydrurus foetidus and Ulotrix zonata ; in the mineralized middle stretches Gomphonema spp., Navicula spp. and Nitzschia spp. are dominant; below the reservoirs the community shifts to a dominance of Achnanthes lanceolata, Amphora pediculus, Melosira varians, Nitzschia dissipata and Fragilaria ulna; in calcareous streams encrusting Cyanobacteria and zygnematales are dominant; and at the mouth and in some polluted areas the diatoms C. meneghiniana, Gomphonema parvulum, Navicula gregaria, Nitzschia palea and N. umbonata are most abundant. Macrophytes are important primary producers in some sections of the river. Below the reservoirs, the macrophytic community is dominated by Myriophyllum verticillatum, P. crispus and P. nodosus. Myriophyllum spicatum and P. pectinatus develop in polluted reaches in the lower river. Bryophytes are mainly found in the headwaters, and Hygrohypnum spp., Philonotis spp., Barbula ehrenbergii, Cratoneuron commutatum, Fissidens rufulus, Fontinalis antipyretica, Cinclidotus fontinaloides, and Leptodictyum riparium are also common at times (Penuelas & Sabater 1987). Headwaters and some tributaries have a diverse macroinvertebrate community (Sabater et al. 1995). Gatherer-collectors, shredders and predators are dominant in the headwaters. Filter-collectors are common in those headwaters influenced by anthropogenic activities. Macroinvertebrates inhabiting the middle river are mainly grazers and filter-feeders, while the collector-gatherers less common in comparison with the upper catchment. The reservoirs affect macroinvertebrate distribution with filtering-collectors being abundant downstream. A pollution-tolerant community is common in the lower river and near the mouth. Two notable invertebrates in the basin are the mussel Unio sp. and the freshwater crayfish A. pallipes-lusitanicus, although both species are becoming less common due to pollution and catchment transformation. In the headwaters thrive the amphibians Euproctus asper and Rana temporaria, while in clean mountain tributaries the salamander (Salamandra salamandra) and the amphibians (Bufo bufo, Alytes obstetricans) are common. Otters (L. lutra) were common in the Ter up to 1950, but since then they have been practically eliminated due to habitat destruction and hunting. Today, the otter has been replaced in some areas by the non-native American mink (Mustela vison).

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The most common fish in the Ter headwaters and mountain tributaries are trout (S. trutta) and barbel (Barbus meridionalis). Downstream, in slower and more temperate waters, the chub (Leuciscus cephalus), barbel and some introduced fishes (B. graellsii, Cyprinus carpio, Tinca tinca) dominate. In the lower reach and near the mouth, some estuary fishes are present (Sostoa 1990). Up to 26% of the fish species have disappeared in the Ter basin from 1940 to 1993 (Camprodon et al. 1995), 33% of them being native. The main causes for the decline include pollution, dam construction, sand extraction and intensive fishing. There are several protected areas in the basin under local management. The Guilleries-Savassona reserve includes a part of the upper Ter as well as that of one main tributary, the Riera Major. It is characterized by its singular geology (Cingles de Tavertet and Montorer). Its riparian habitat hosts several amphibian species (such as Triturus marmoratus, S. salamandra, B. bufo, Rana perezi) and birds (Ardea cinerea, Phalacrocorax carbo, Larus cachinnans). The Montesquiu reserve area is in the middle-upper basin and comprises an important calcareous area with remarkable slab-bottom streams. In the lower Ter, there is a small protected area that includes valuable wetlands and the estuary (Ter Vell). A marine reserve (Medes Islands) is directly affected by the Ter’s water plume. Several areas distributed along the basin are trying to achieve special protection to maintain the Ter basin as a natural green corridor. The Water Framework Directive is progressively being implemented in the Ter basin by the Catalan water authority (ACA; Agencia Catalana de l’Aigua).

4.7.6. Conclusions and Perspectives The Iberian Peninsula has a variety of climates and geological settings that are expressed in a diversity of fluvial regimes, geochemistry and biological diversity. The human influence in the Iberian Peninsula has existed for many centuries, well before the Romans conquered the Peninsula. These two factors need to be taken together to understand the present situation that defines the Iberian rivers. Most of the Iberian Peninsula is semi-arid in terms of rainfall. Although the Mediterranean basin is smaller than the Atlantic basin, there is a northeast to southwest gradient in aridity that affects both. This effect causes some Iberian rivers to have lower water flows than similar systems throughout Europe, and is extreme in the southernmost Mediterranean streams that can be intermittent during the summer. In these streams, rains are concentrated in short periods of time and can cause catastrophic floods. The natural shortage of water and the irregularity of flow in the rivers have influenced the historical relationship between the rivers and humans. Hydraulic infrastructures were already implemented by the Romans and Arabs, and reached a construction peak during the 20th century with the construction of hundreds of medium and large reservoirs. Agri-

PART | I Rivers of Europe

cultural use and protection against floods promoted the construction of large dams in the Iberian Peninsula. The magnitude of infrastructure and its associated management have had lasting and irreversible effects in the geomorphology of many rivers of the Iberian Peninsula. Presently, the Iberian Peninsula watercourses are highly regulated, possibly among the highest in Europe. Additional effects beyond flow regulation include a reduction in floodplain areas, a reduction in meanders and the loss of riparian zones, as well as a lowering of the water table in several basins. In the Tagus, up to 55% of the original riparian zone is gone and nearly 90% in some of its tributaries. In the Guadiana, a decrease in the water table is threatening unique ecosystems such as the Tablas de Daimiel. Its restoration is difficult because it would demand a complete reappraisal of current agricultural practices. The natural water scarcity along with intense water use cause poor water quality in several stretches of most Iberian rivers. Water purification has been implemented in only a few basins, while, in others, it is limited to large cities and results in high inputs of organic matter and dissolved nutrients from smaller communities. This may be especially problematic during summer low flows. Although the progressive implementation of the WFD throughout Iberia is a hope to ameliorate this situation, the effects are still noticable in several systems and periods during the year. Eutrophication affects a large number of rivers in the Iberian Peninsula. A recent official report (Spanish Ministry of Environment 2005) stated that nearly 50% of the water stored in reservoirs is affected by eutrophication, in particular in the Tagus, Guadiana and Guadalquivir catchments. The percentage of subterranean waters affected by nitrate contamination in the Iberian Peninsula ranges between 15% and 19%. Iberian rivers are naturally rich in terms of their biota. Biogeographically, the Peninsula has taxa from Europe in the north and North Africa in the south. This boundary has historically influenced the high diversity of the inland waters in the Iberian Peninsula. The Guadiana basin holds up to 15 endemic fish. The high richness is true for Crustacea to fishes, and also algae and macrophytes (Margalef 1983). The Donana marshes in the Guadalquivir host an enormous biological diversity in a rather patchy aquatic environment. The biological richness in Iberian inland waters is currently under threat because of the high number of biological invasions. For example, the river Ebro has recently been invaded by the molluscs D. polymorpha and C. fluminea, but also by the fishes S. glanis and Ictalurus melas in its lower course. These invasions have resulted in a decrease in habitat diversity and in the number of native species. Water transfer between basins is a constant issue in the different hydrological plans that the governments develop to satisfy the high water demands (Plan Hidrologico Nacional 2001), and which would increase the possibility for species invasion. The management of rivers and their associated disturbance regimes has a cultural or societal component. The human presence and management of watercourses may have

Chapter | 4 The Iberian Rivers

very different affects depending on the cultural perception of rivers. People in arid and semi-arid regions have the least respect towards rivers since the rivers are often dry or have catastrophic floods, and are therefore viewed more as a danger than as a natural resource to be preserved. Moreover, there is a well-rooted perception that any water that reaches the sea is wasted. This perception being difficult to change, the progressive implementation of the WFD in the different basins will hopefully force a change in attitude towards the rivers, as well as the required administrative steps to secure their conservation and sound management.

Acknowledgements Most of the data shown in this chapter have been patiently collected by the staff of the different Hydrologic Basin Authorities (Spain) and INAG (Portugal), to whom we are extremely grateful. Arturo Elosegi read and corrected the section on the Ag€ uera River. Gemma Vidal assessed of the references. The writing of this chapter benefited from funding by the Commission of the European Community (Modelkey, Contract-No. 511237, GOCE).

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PART | I Rivers of Europe

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Chapter | 4 The Iberian Rivers

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PART | I Rivers of Europe

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FURTHER READING ICONA, 1991. Peces continentales espanoles. Inventario y clasificacion de zonas fluviales., Madrid, 221 pp.

RELEVANT WEBSITES http://www.spea.pt/IBA: Sociedade Portuguesa para o Estudo das Aves.  Important Bird Areas. http://www.mma.es/portal/secciones/acm/aguas_continent_zonas_asoc/: Spanish Environment Ministry, general information on inland waters. http://www.mma.es/secciones/biodiversidad/rednatura2000/rednatura_espana/: Natura 2000 network in Spain http://www.gencat.net/aca: Catalan Water Agency. Information about the internal water bodies of Catalonia (Ter and others). http://www.chtajo.es/: Confederacion Hidrografica del Tajo. Data, Maps and reports of the Tagus catchment http://www.chj.es/: Confederacion Hidrografica del Jucar. Data, Maps and reports of the Jucar catchment

Chapter | 4 The Iberian Rivers

http://ec.europa.eu/environment/water/index_en.htm. http://viso.ei.jrc.it/wfd_prb/index.html. The Jucar River basin as a pilot project of the European WFD. http://www.chebro.es/: Confederacion Hidrografica del Ebro. Data, Maps and reports of the Ebro catchment. http://www.chsegura.es/: Confederacion Hidrografica del Segura. Data, Maps and reports of the Segura catchment.

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http://www.chduero.es/: Confederacion Hidrografica del Duero. Data, Maps and reports of the Duero catchment. www.chguadalquivir.es Confederacion Hidrografica del Guadalquivir. Data, Maps and reports of the Guadalquivir catchment. http://www.chguadiana.es/: Confederacion Hidrografica del Guadiana. Data, Maps and reports of the Guadiana catchment.