Palaeoproductivity and environmental changes during the Holocene in central Italy as recorded in two crater lakes (Albano and Nemi)

Quaternary International 88 (2002) 57–68

Palaeoproductivity and environmental changes during the Holocene in central Italy as recorded in two crater lakes (Albano and Nemi) P. Guilizzonia,*, A. Lamia, A. Marchettoa, V. Jonesb, M. Mancaa, R. Bettinettia b

a CNR Istituto Italiano di Idrobiologia, 28922 Verbania Pallanza, Italy Environmental Change Research Centre, University College London, 26 Bedford Way, WCH1 OAP London, UK

Abstract Three cores from two crater lakes in central Italy (Albano and Nemi) spanning the last ca. 11 kyr BP are discussed here. They were analysed for organic matter, dry density, algal and photosynthetic bacteria pigments, diatoms and Cladocera. These palaeolimnological records show great internal consistency in their response to distinct, but inter-related, aspects of the lakecatchment system, and reflect major changes in these systems particularly in lake productivity. The early Holocene was characterised by very high productivity at both sites. Trends in productivity are similar for many proxies in the Holocene records of Lake Albano and Lake Nemi. Trophic levels throughout much of the period of human activity (ca. 4000 yr BP onward) are lower but have remained relatively high and stable at both lakes. It is only in the last few decades that inferred productivity levels have exceeded those of the early Holocene. Statistical analysis (CONstrained Incremental Sum of Square cluster analysis, CONISS) showed five distinct periods during the Holocene characterised by major variations in the abundance and community structure of biological remains and geochemistry. A comparison of results from the different taxonomic groups has enabled the reconstruction of phases of increased productivity and the recognition of signals of anthropogenic impact on the lakes and their catchments. From published pollen diagrams, nine major deforestation events are recognised during the Holocene. These events, in particular the one which occurred in both lakes at 1800 yr BP and identifies the Roman Period, plus another at 3000–3500 yr BP related to agricultural activity during the Bronze Age, produced profound changes in the pelagic community structure of diatoms and Cladocera, which in some cases were even more marked than the accelerated eutrophication seen in recent times. The mid-Holocene climatic transition is also clearly evident and is characterised by a strong decrease in the concentrations of the biological proxies. Most of the observed lacustrine environmental changes are almost synchronous in the two lakes indicating the importance of regional rather than local changes. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.

1. Introduction During the last decade several large projects have focussed on the impact of environmental and climatic factors as recorded in maar lake deposits. These have shown the potential for detailed reconstructions of natural and anthropogenic changes (e.g. Negendank and Zolitschka, 1993; Guilizzoni and Oldfield, 1996; Siffedine et al., 1996). Maar sediments are commonly varved and thus provide excellent chronological resolution, while the small catchment areas of such lakes may amplify the proxy palaeoclimatic signals. Central and South Italy provide a rich and sensitive region and a challenge for palaeoclimatologists, having numerous sites located in a critical area in terms of pattern, periodicity and expression of Quaternary climatic change (Kelly and Huntley, 1991; Francus *Corresponding author.

et al., 1993; Guilizzoni and Oldfield, 1996; Watts et al., 1996a, b; Ramrath et al., 1999a, b). Besides, the Mediterranean region is clearly one of extreme vulnerability to the combined effects of climate and human activities. Reconstruction of vegetation and climate changes on the central and southern Italian peninsula during the Holocene and late Pleistocene have been reported from several lake records (e.g. Hutchinson, 1970; Kelly and Huntley, 1991; Follieri et al., 1993; Mergeai, 1995; Guilizzoni and Oldfield, 1996 and references therein; Watts et al., 1996a, b; Zolitschka and Negendank, 1996; Allen et al., 1999). Climatic and tectonic histories of lakes in the Latium Region have also been studied (Niessen et al., 1993; Vigliotti et al., 1999; Ramrath et al., 2000). This paper focuses on palaeoproductivity and environmental changes during the Holocene as revealed by multi-proxy analysis of sediment cores from the crater lakes Albano and Nemi (central Italy). In particular, we

1040-6182/02/$ - see front matter r 2002 Elsevier Science Ltd and INQUA. All rights reserved. PII: S 1 0 4 0 - 6 1 8 2 ( 0 1 ) 0 0 0 7 3 - 8

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highlight and synthesise some of the main results derived from a range of lacustrine biological remains (pigments, diatoms and Cladocera). We also discuss results (e.g. chironomids, complete taxa profiles of diatoms and Cladocera) from former investigations (Ryves et al., 1996; Manca et al., 1996). The core sections were also analysed in detail for dry density, organic matter content, preserved pigments (chlorophylls and carotenoids from algae and sulphur photosynthetic bacteria). We seek to unite and compare the lacustrine archives to reconstruct both the pattern and amplitude of primary climatic forcing and the nature of aquatic ecosystem responses to this forcing for the Holocene record (last ca. 11 kyr BP). The important reason for working on sites that are closely located is that one can distinguish site-specific signals from those reflecting regional events. If non-synchronous changes are shown, then local hydrological variables will be more important than regional (atmospheric) changes. In contrast, strong parallelism in proxy records from the sites should indicate a regional ‘orchestration’ of the changes. Fossil pigments can serve as valuable indicators of past environments and can act as indices of present and past trophic conditions (e.g. Guilizzoni et al., 1983; Leavitt, 1993). Since many of the factors that control trophic state and lacustrine primary productivity are climatically related, plant pigments as well as biological fossil remains are useful in obtaining information on palaeoenvironment and palaeoclimate (Sanger, 1988; Leavitt et al., 1997; Vinebrooke et al., 1998). Diatoms are sensitive ecological indicators and have been widely used to quantify past changes in pH (Battarbee and Renberg, 1990), salinity (Fritz, 1989) and nutrients (e.g. Bennion, 1994), and transfer

functions have been established for several regions (Battarbee, 2000). Cladocera give an insight into the pelagic environment and have been extensively used as indicators of changes in primary productivity, pH and water level variations due to both anthropogenic and climatic effects (Frey, 1974; Hann et al., 1994; Palacios-Fest, 1994). Quantitative reconstruction of these environmental variables is possible where transfer functions are available. In addition, changes in predation pressure as well as alteration of the pelagic food web induced by different types of disturbances, can be seen from their body size, biomass, population structure and taxonomic composition (Kerfoot, 1974; Kitchell and Kitchell, 1980; George and Harris, 1985; Carpenter et al., 1986; Hann et al., 1994).

2. Study sites Lakes Albano and Nemi occupy two craters in the complex Alban Hills caldera about 10 km south-east of Rome (Fig. 1). A detailed review of the geology of the area, as well as the physiographic, hydrological, morphometric and limnological features of these lakes, is given by Niessen et al. (1993) and Chondrogianni et al. (1996a). Table 1 summarises the main morphological characteristics. Both lakes are hydrologically closed basins, receiving water mainly from atmospheric precipitation and underwater springs. In order to facilitate recovery of two Roman ships the water level in Lake Nemi was artificially lowered by 23 m between 1928–1932, and the original level was re-established in 1943 (Stella et al., 1978).

Fig. 1. The Mediterranean area, lakes and cores location.

P. Guilizzoni et al. / Quaternary International 88 (2002) 57–68 Table 1 Location and main morphometric characteristics of the lakes Albano and Nemi Lake Albano Latitude Longitude Max. depth (m) Mean depth (m) Residence time (a) Surface area (km2) Catchment area (km2)a Volume (109 m3) a

0

41145 N 121400 E 175 77 47 6 3.68 0.5

Lake Nemi 411430 N 121430 E 32 17 15 1.8 10.3 0.03

Lake area excluded.

The present-day limnology of Lake Albano shows that below ca. 100 m oxygen is absent all year around and the lake is characterised by meromictic and mesoeutrophic conditions. Reactive phosphorus and N-NH4 range from zero in the epilimnion to ca. 170 and 500 mg l
1 in the hypolimnion, respectively. In contrast, N-NO3 concentration is high (ca. 200 mg l
1) in the epilimnion and zero in the hypolimnion. pH along the whole column ranges from ca. 8.0 (surface) to ca. 7.0 (bottom). High concentrations of CO2 (ca. 200 ppm) in the bottom water have been measured by Martini et al. (1994) and interpreted as reflecting an input from volcanic gases. The phytoplankton assemblage is dominated by cyanobacteria, Chlorophyceae, and diatoms. Lake Nemi is a much more productive environment with frequent blooms of cyanobacteria (e.g. Oscillatoria rubescens) and it lacks oxygen in the hypolimnion during summer stratification. Nutrient concentrations are high: total P is ca. 90 mg l
1 for most of the year. pH values range from 9.0 in the epilimnion to 7.5 in the hypolimnion. In contrast to Lake Albano, alkalinity is lower in Lake Nemi ranging from 2.86 (surface) to 3.10 meq l
1 (bottom). Alkalinity is quite high in both lakes and it reflects the geological features of the catchments.

3. Methods A seismic survey of lakes Albano and Nemi identified suitable sites for coring and several cores were taken in June 1994 using a Kullenberg piston corer (Chondrogianni et al., 1996b). The cores discussed here were collected at a water depth of 70 m (PALB 94-1E, 13.875 m long; the Holocene spans the topmost 5.30 cm) and 120 m (PALB 94-3A, 12.20 m long) in Lake Albano, and at 30 m in Lake Nemi (PNEM 94-1B, 9.15 m long). These are hereafter referred to as cores 1E, 3A and 1B. In core 1E a hiatus representing ca. 2500 yr was identified in the Holocene interval. Although core 1E spans a longer period (ca. 30 kyr;

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Guilizzoni et al., 2000), only the Holocene part is described here. The whole cores 3A and 1B spans the last ca. 11.5 kyr. The sediment cores were sub-sampled every 2–10 cm in 1–2 cm increments with closer sampling over sections displaying marked changes in lithology. The Cladocera remains in Lake Albano were analysed at a lower resolution compared to Lake Nemi for the last 4 kyr BP. The temporal resolution is roughly decadal for part of the geochemistry record (pigment included) whilst most of the other proxy-records are at century scale. Organic matter content was estimated by loss on ignition (LOI) at 5501C. Total pigments (chlorophyll plus chlorophyll derivatives, CD; and carotenoids, TC) were extracted with 90% acetone. For comparison with previous studies, chlorophyll derivatives were calculated as absorbance units per gram organic matter (Adams et al., 1978), whereas total carotenoids were expressed as mg per gram organic matter. Specific algal and sulphur bacterial pigments were determined by ion pairing, reverse-phase HPLC and expressed as nMoles per g organic matter to avoid problems of dilution with clastic material entering from the catchment (Lami et al., 1994). Pigment preservation, and thus the quality of pigment data, can be assessed by a variety of sedimentary indices. One is given by the native chlorophyll, i.e. the proportion of chlorophyll not degraded to phaeopigments (Swain, 1985), and another is the ratio 430 nm: 410 nm (ratio between the spectrophotometric absorbencies of acetone extract at the two above wavelengths), i.e. the degree of conversion of chlorophyll to phaeopigments as a measure of the state of conservation of the pigments in the sediment (Guilizzoni et al., 1992). Conditions for pigment preservation are generally good in both Lake Albano and Lake Nemi (Ryves et al., 1996). Diatoms were prepared using standard digestion procedures (Battarbee, 1986). Diatom frustules were identified and counted using both light (  1250) and electron microscopy. To analyse fossil Cladocera, a known weight of wet sediment (about 1 g) was deflocculated in warm 10% KOH for 2 h and then digested in HCl 10%. The remaining concentrate was then transferred into 5% formalin. We counted up to 200 remains per sample identifying them to genus or species (Manca et al., 1996). The data for biological remains are expressed as relative percentages and in absolute counts per gram of dry sediment (No. mg-1 d.w.). CONISS (CONstrained Incremental Sum of Squares cluster analysis), with square root transformation to optimise the signal to noise ratio, was used for the analysis of geochemical and pigment data only; these were the only data common to all cores.

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4. Results and discussion 4.1. Chronology Based on four AMS radiocarbon dates from core 3A (calibrated according to Stuiver and Reimer, 1993), core correlations, tephra chronology and pollen, the boundaries between Late Glacial/ Holocene and the age-depth for the Holocene period were established for each core (Fig. 2). The correlation of palaeomagnetic directional data and a geomagnetic master curve from other dated cores (e.g. Thouveny et al., 1990; Guilizzoni et al., 2000), were also used to precisely date the cores. One welldated tephra layer (‘‘Avellino’’ tephra; Calanchi et al., 1996) was detected in cores from both lakes and used as an absolute time marker (4.1 cal. kyr BP; 4.02 kyr cal. BP according to Ramrath et al., 2000) as well as for core correlation. Detailed between-core correlations at each site were also obtained from high-resolution magnetic susceptibility measurements (Rolph et al., 1996) and by planktonic diatom analysis. In the case of the core from Lake Nemi no 14C dates were available due to the lack of any terrestrial woody remains. However, the ages reported for this core were obtained from a number of estimates based on the correlation of (1) whole core magnetic (Rolph et al., 1996 and paper in preparation) and pigment data, (2) the ‘‘Avellino’’ tephra marker, and (3) pollen diagrams from Lake Albano, and a southern crater lake, Monticchio (Watts et al., 1996b). The chronology is also consistent with the date at which Zea mais pollen is first encountered, the Roman cultivation of Juglas, Castanea and Cannabis. Besides, a new more detailed age-depth model is in progress and this may change the upper ca. 2 m of the core chronology (T. Rolph and L. Vigliotti, personal communications). Lead-210 analysis and varve counts were applied to the recent sediment (Masaferro et al., 1993; Lami et al., 1994; Alvisi and Frignani, 1996). 4.2. Sediment features Using CONISS chemical and pigment data sets, the cores 1E, 3A (L. Albano) and 1B (L. Nemi) were split into zones. Five main zones of similar duration and of similar onsets (except zone IV) were identified in both lakes (Fig. 3). The Holocene sediments of lakes Albano and Nemi are rich in organic material (ca. 20% d.w.). The sedimentation rates are estimated to range from 0.042 to 0.058 cm yr
1 (core 1E), 0.071–0.12 cm yr
1 (core 3A) and 0.061–0.16 cm yr
1 (core 1B). There appear to have been several sudden changes in stratigraphy on a century time scale (between ca. 200 and 700 yr) in the early middle Holocene period (Figs. 3–5). For example, there is a noticeable sharp reduction in dry density in both lakes (most evident in L. Albano) at ca. 9700 yr BP

Fig. 2. Calendar age-depth curves for the three study cores: PAL94 3A and PAL94 1E from Lake Albano, PAL94 1B from Lake Nemi. The different types of evidence are also indicated (i.e. 14C, tephra layer of ‘‘Avellino’’ Plinian eruption from Somma-Vesuvius volcanic centre, pollen peaks, master palaeomagnetic curve) and used to establish the chronology.

(zone I; Fig. 3), and there are numerous peaks in dry density during the early and mid-Holocene (zones II and III). A common peak is also evident around 1800 yr BP when major deforestation occurred in both catchments and which is also evident in the Central Adriatic cores (Lowe et al., 1996). Several marine cores analysed in the

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Fig. 3. Summary of lacustrine records of Holocene palaeoenvironmental changes from lakes Albano and Nemi sediment cores. Zones I–IV resulting from cluster analysis (CONISS) of all the available chemical and pigment data from cores 3A (L. Albano) and 1B (Lake Nemi) are also indicated. T=‘‘Avellino’’ tephra. HOL/YD=Holocene/Younger Dryas transition.

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Fig. 4. Summary of fossil diatoms from two cores from lakes Albano and Nemi. Single taxa are expressed as percentages whereas total cells as concentration. T=‘‘Avellino’’ tephra, HOL/YD=Holocene/Younger Dryas transition.

Fig. 5. Summary of fossil Cladocera from two cores from lakes Albano and Nemi. Single taxa are expressed as percentages whereas total remains as concentration. T=‘‘Avellino’’ tephra. HOL/YD=Holocene/Younger Dryas transition.

PALICLAS project provided high-resolution records of the Holocene and all show clear evidence of widespread deforestation from the Mesolithic period onwards (Guilizzoni and Oldfield, 1996). A major change in allochthonous minerogenic input, which could be related to deforestation, is also seen in lakes Mezzano and Monticchio (Ramrath et al., 1999a, b), suggesting a regional climate forcing. Particularly evident in the continental (lakes Nemi, Albano, Mezzano, Vico and

Valle di Castglione; Ramrath et al., 2000) and marine records are the two main phases of forest clearance and increased cultivation that took place between 3600 and 3000 yr BP and around 700 yr BP (Oldfield et al., 2000). Many parts of the record in both lakes are annually laminated (zone II in core 1E; almost all core length for cores 3A and 1B). In these laminated sections the pigments belonging to anaerobic, sulphur bacteria are more abundant (see below).

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In general the concentrations of pigments in Lake Nemi are much higher compared to those from Lake Albano. The presence of photosynthetic sulphur bacterial carotenoids (i.e. okenone and isorenieratene) in early and mid-Holocene (zone II; 10–5 kyr BP) is significant (Fig. 3). These pigments, however, are also abundant throughout much of the Holocene, except in the mid Holocene (zone III). These organisms proliferate in strictly anoxic conditions in the presence of H2S in lake waters or at the water/sediment interface (Zullig, . 1985). Cyanobacterial pigments (as sum of specific algal carotenoids such as echinenone, oscillaxanthin, myxoxanthophyll and zeaxanthin) characterise the early phase of the Holocene (zone II), although there are very few in zone I, their concentrations rise near the top of the core (zone V; Fig. 3). These periods of high concentration are phases of fairly high lake productivity with a seasonally anoxic water column. They are separated by colder, oligotrophic periods as inferred from the diatoms (see below), Cladocera (Figs. 4 and 5) and chironomid remains (not shown: see Manca et al., 1996). Six clear events of high pigment peaks occurred in zone II (Fig. 3). The balance of evidence from Lake Albano sediments (e.g. presence of varves, high percentages of planktonic communities) points to substantially higher lake levels during these periods. In contrast, the lake level was lower in Lake Albano between 3000 kyr BP and 3500 yr BP, a period during which a human settlement was established on the lake shore (Chiarucci, 1985) and nearby lakes (Magri, 1999). No information about settlements in that period is available from Lake Nemi. The concentrations of algal and bacterial pigments are remarkably low at ca. 9.5, 8.5, 6 kyr BP, between ca. 5.0 and 3.8 kyr BP as well as at 1800 yr BP. The absence or reduction in concentrations of photosynthetic sulphur bacteria in many periods of the Holocene (e.g. between 5000 and 4000 yr BP; zone III) is very likely related to high water turbidity (high concentrations of dry density is noted here) which limited light availability and hence the bacterial development.

1990). As a whole, for very long periods of the early to mid-Holocene, ‘‘small’’ Stephanodiscus (S. minutulus) dominated over Cyclotella ocellata, indicating generally meso-eutrophic conditions (cf. Bennion et al., 1995) Similar species successions have been observed in other lakes experiencing nutrient enrichment (Battarbee, 1978; Nimmergut et al., 1999). The early Holocene is characterised by a diatom signal primarily consisting of simultaneous planktonic blooms of several small Stephanodiscus taxa. The diatom concentrations are much lower in the more eutrophic Lake Nemi. Silica concentrations are reduced in productive lakes and usually cyanobacteria have a competitive advantage and predominate over diatoms (Wetzel, 1975). We do not think that frustule dissolution is an important process in Lake Nemi since the most important chemical factors such as alkalinity, pH and generally hard water conditions (Brugam, 1983), are lower in this lake, or very similar to Lake Albano. A distinct difference between the lakes is the reduction of Stephanodiscus in Nemi between 4 kyr BP and 2000 yr BP (Fig. 4) suggesting that the lake became less productive. In this period in Lake Albano, Stephanodiscus spp. and Cyclotella spp. coexist. At ca. 2000 yr BP Stephanodiscus spp. increases and S. hantzschii is also abundant; this indicates a gradual increase in trophic state in both lakes, which can be linked to anthropogenic impact. Previous work has suggested that the onset of human interference on catchments (such as the forest clearance and their replacement with agricultural land use, e.g. Castanea, Juglans, Olea at ca. 2700–3000 yr BP (Lowe et al., 1996; Accorsi et al., in preparation; Guilizzoni and Lami, 1999) is linked to increasing nutrient inputs (e.g. phosphorus) and elevated nutrient levels in surface waters (Ryves et al., 1996). The rise in small Stephanodiscus taxa before this period may be independently linked to the climatic amelioration of the early mid Holocene (9000–5000 yr BP). Thus, for the first half of the Holocene, the close correspondence between the main diatom and pollen zones suggests that climate is likely to be an important determinant on lake levels and changing aquatic productivity.

4.4. Diatoms

4.5. Cladocera

The diatom assemblage in the cores from both lakes Albano and Nemi is dominated throughout the core sequences by centric, planktonic taxa (often over 80%) and during the first half of the Holocene the diatom floras are very similar at both sites (Fig. 4). The diatom abundance in both lakes is highly variable but the highest values are coincident with the largest peaks in Stephanodiscus spp. (S. parvus and S. minutulus). In contemporary systems, small Stephanodiscus taxa are linked to highly eutrophic waters (Anderson et al.,

The concentration of total Cladocera remains is generally very low in the early Holocene sediments (Fig. 5). Predator Cladocera in Lake Nemi are far more strongly represented than in Lake Albano, confirming a relatively higher trophic status than Albano. Daphnia dominates from the onset of the Holocene to ca. 7.5–6.5 kyr BP. Then it declines, first in Lake Albano (at ca. 7.5 kyr BP), then in Lake Nemi (at ca. 6.7 kyr BP), and Bosmina becomes dominant. In Lake Nemi in the mid-Holocene deposits, from ca. 4700–3500 yr BP,

4.3. Pigments

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the concentration of remains (and pigments) is relatively low and Daphnia spp. is again dominant, followed by a sharp increase in Bosmina. In both lakes Daphnia longispina gr. is the most representative zooplanktonic Cladocera. In Lake Nemi the Cladocera remains fluctuate more (probably due to the different sampling resolution) and some peaks are out of phase with the Lake Albano assemblages. However, the major rise in the total assemblage at 3.5 kyr BP is common in both lakes. Similarly, in both lakes Daphnia spp. is replaced by Bosmina spp. from 7.5 and 7.0 kyr BP, respectively, up to 5.0 kyr BP, and then again there are a number of fluctuations in these two cladocerans during the last 3.5 kyr (Fig. 5). The replacement of Daphnia by Bosmina and the decrease in size (Manca and Comoli, 1996) indicate a period of increased (1) predation pressure by fish (Kerfoot, 1974) and a low grazing efficiency of herbivores (Kitchell and Kitchell, 1980; Leavitt et al., 1994), (2) productivity and (3) total in-lake phosphorus concentration (Jeppesen et al., 1996; see Manca et al., 1996 for further discussion). In the early middle Holocene (10–4 kyr BP) of Lake Albano a large number of chironomid remains were also observed, especially in the layers between 8.4–8.5 kyr BP and at 3.9 kyr, suggesting an improvement in climate (warmer and more humid) and a greater development of littoral aquatic vegetation (Manca et al., 1996). In both lakes the shifts from a Daphnia-dominated to a Bosmina-dominated community match quite well the forest clearances (Table 2; cf. Lowe et al., 1996). For the last ca. 3 kyr BP these changes are a clear sign of human impact, which can also be detected from pollen data, revealing the beginning of cultivation of edible fruit plants (Lowe et al., 1996; Guilizzoni and Lami, 1999). The Bosmina-phase, which shows many fluctuations in Lake Nemi, may also indicate high predation pressure by fish and a low grazing efficiency of the zooplanktonic herbivore community (Leavitt et al., 1994), the latter also evident from phaeophorbide a concentration. This unique chlorophyll derivative pigment is formed by herbivores and can be used to monitor grazing pressure Table 2 Occurrence of deforestation (cal. yr BP) in the catchments of lakes Albano and Nemi (years calibrated BP) Lake Albano

Lake Nemi

207 700–730 1160 1800 3000 3650–4000 5100 6450–6680 10150–10450

112–160 575–680 1800 3240 3500–3890 4100–4900 5040–5500 6740 9900–10200

(Leavitt, 1993). The Cladocera concentration peak at ca. 2.7 kyr BP and ca. 3.0, respectively, in Albano and Nemi corresponds to the maximum abundance of chydorids and to a peak in pollen concentrations. Although Bosmina spp. are by far the dominant taxa, the presence of Diaphanosoma at ca. 1.1 kyr BP in Lake Albano, indicates mean summer water temperatures of about 201C and a well-established summer thermocline (Herzig, 1984). During the last 5–6 centuries the concentration of Daphnia remains (and the planktivoricity index, i.e. Bosmina/Daphnia+Bosmina ratio; Kitchell and Kitchell, 1980) increases indicating a high degree of grazing pressure by zooplankton on phytoplankton. Also the qualitative and quantitative composition of chironomid remains observed in this period reflects an increase in the trophic status of the lake following anthropogenic impact. This human effect is also well seen in another lake of Latium, Lake Mezzano, for which archaeological data confirm the presence of several settlements and corresponding human activity in the catchment (Ramrath et al., 2000). The very detailed analysis of recent sediments in Lake Nemi refers to the abrupt artificially lowering of the water level of the lake during 1930–1940, to recover two Roman ships (Masaferro et al., 1993). Specific investigations of the plankton community revealed a sudden eutrophication of the lake and a general impoverishment of the community (Marchesoni, 1940; D’Ancona, 1942). The impact is also very clear in the sedimentary record with a large increase in concentration of rotifer resting eggs, and a decrease in zooplanktonic Cladocera. During the last few decades Daphnia increases sharply, documenting a re-establishment of the zooplanktonic community of Lake Nemi.

5. Summary and conclusions Similarities in the environmental history of the two lakes are evident and these are reflected in the pigment and biological proxy records in the studied cores (Fig. 3). There are also some differences between the two lakes, which may stem from their distinct bathymetry, catchment size and disturbance (e.g. forest clearance; see Table 2), topography and temporal resolution. The significant of the choice of these lakes in this study lies in the demonstration of the sensitivity of their sediment record to environmental change, the qualitative and quantitative documentation of high levels of climatically forced variability. Algae and Cladocera responded promptly to the most important natural variations in the lake water level and climate and/or anthropogenic events, with changes in concentrations as well as in community structure. High erosion rates, low primary productivity, high water level

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and mainly aerobic conditions characterised the early Holocene (11.2–10 kyr BP; zone I). Then, from ca. 10 kyr BP, high productivity levels appeared during the first half of the Holocene (zone II), a period in which inferred primary productivity (and total water phosphorus concentrations) reached values found in very eutrophic lakes today (climatic optimum). However, in both lakes six clear major abrupt changes in pigment concentrations (and to some extent LOI too) occurred in zone II and partially in zone III (Fig. 3), which were probably associated with climatic deterioration (e.g. the widespread cold events at ca. 8.0–8.4 kyr BP; Alley et al., 1997; Barber et al., 1999). The balance of evidence from Lake Albano sediments (e.g. presence of varves, high percentages of planktonic communities) points to substantially lower lake levels during minimum pigment concentrations. In the mid-Holocene (overall in zone III; Fig. 3), a sudden increase in minerogenic clastic input, accompanied both by a sharp decline in pigment concentrations and in biota densities, has been interpreted from a complex of proxy-records (e.g. pollen, sediment magnetic properties) as the first discernible impact of human activity in the catchment (Oldfield, 1996; Table 2). However, it is also possible, as seen in other lake sequences in Europe and in Italy (Ariztegui et al., 1996; Orombelli and Ravazzi, 1996; Magri, 1997; Ramrath et al., 2000), that the lowering in primary productivity between ca. 5.5 and 4.0 kyr BP (zone III, Fig. 3) is the result of superimposed climate change. From pollen studies carried out in central Italy (Magri, 1997), this period is characterised by an increase in wetness. The natural minerogenic inputs generally lowered the productivity of the lake (high influx of particles=high turbidity=low photosynthesis) and when, for instance during Roman times, the lake was probably subjected to nutrient enrichment, the effect on algae was, except in very recent times, less marked than that derived from the natural impact noted during the early Holocene (Lami et al., 1996, 1997). After ca. 3.5–3.0 kyr BP, the productivity (and TP levels) rose to a more sustained high level (zone IV) and remained high until recent times. In general, concentrations of pigments, especially those of cyanobacteria, are higher in Lake Nemi compared to contemporaneous levels in Lake Albano; this may imply a lower anthropogenic nutrient enrichment of L. Albano. Moreover, oscillations in lake productivity, as inferred for the fossil pigments and diatoms mainly, can be compared with major terrestrial vegetation changes (forest clearance) reported for the lakes. The nine deforestation events apparent in the pollen diagrams from both lakes from (Table 2), in particularly the one that occurred simultaneously in both catchments at 1800 yr BP, and the agricultural activity during the late Holocene was accompanied by

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evident alterations in the assemblages of diatoms and pelagic Cladocera, changes that in some cases were similar to those of the accelerated eutrophication of recent times. The close link between catchment surface processes and in-lake productivity is shown by the relationship between forest clearance and the Cladocera assemblages of lakes Albano and Nemi, which shifted from Daphnia to Bosmina (Fig. 5). Similar response was observed in Lago Grande di Monticchio in which any relative lag in the response in the vegetation was less that ca. 60 yr minimum time resolution for that record; Nimmergut et al., 1999). In conclusion, this study also confirms that the Holocene in central Italy was not a stable period and that climate changes and anthropogenic disturbances had very important impacts on the lake ecosystems (Ramrath et al., 2000; Ariztegui et al., 2001). Signals of marked changes detected in sediment record in the last ca. 4000 yr BP are mostly anthropogenic, whereas, for example, the sudden, clear general decrease of all the biota around 5000–4000 yr cal. BP and the fluctuations between ca. 2000 and 3000 yr BP can also be associated with the central Italy cool-wet and dry phase periods, respectively (Magri, 1997). In general, most of the major observed changes and signals reflect regional events rather than local hydrological variables. This is confirmed by a recent study in which the Holocene changes in lakes Albano and Nemi correlated well with the timing of Mediterranean Sea changes, e.g. the warm and humid, high productivity period of sapropel formation between 9.5 and 6.0 kyr BP, the mid Holocene and the 8.5–7.5 cool phase with low productivity (Ariztegui et al., 2000; Oldfield et al., 2000).

Acknowledgements We are grateful to A.M. Mercuri, C.A. Accorsi, S. Juggins and the PALICLAS colleagues for many useful and open discussions on pollen data and chronology. We very much appreciated the constructive and helpful comments by two referees. This study was supported from the EU project PALICLAS (Contract EV 5VCT93-0267, DG XII-FZPA). This is a contribution to the European Lake Drilling Programme (ELDP).

References Adams, M.S., Guilizzoni, P., Adams, S., 1978. Sedimentary pigments and recent primary productivity in northern italian lakes. Memorie dell’Istituto italiano di Idrobiologia 36, 285–287. Allen, J.R.M., Brandt, U., Brauer, A., Hubberten, H.W., Huntley, B., Keller, J., Kraml, M., Mackensen, A., Mingram, J., Negendak, J.F.W., Nowaczyk, N.R., Oberhansli, H., Watts, W.A., Wulf, S., Zolitschka, B., 1999. Rapid environmental changes in southern Europe during the last glacial period. Nature 400, 740–743.

66

P. Guilizzoni et al. / Quaternary International 88 (2002) 57–68

Alley, R.B., Mayewski, P.A., Sower, T., Stuiver, M., Taylor, K.C., Clark, P.U., 1997. Holocene climatic instability: a prominent, widespread event 8200 yr ago. Geology 25, 483–486. Alvisi, F., Frignani, M., 1996. 210Pb-derived sediment accumulation rates for the central Adriatic Sea and the crater lakes Albano and Nemi (central Italy). In: Guilizzoni, P. and Oldfield, F. (Eds.), Palaeoenvironmental Analysis of Italian Crater Lake and Adriatic Sediments (PALICLAS), vol. 55. Memorie dell’Istituto italiano di Idrobiologia, pp. 303–320. Anderson, N.J., Rippey, B., Stevenson, A.C., 1990. Change to a diatom assemblage in a eutrophic lake following point source nutrient re-direction: a palaeolimnological approach. Freshwater Biology 23, 205–217. Ariztegui, D., Farrimond, P., Mckenzie, J.A., 1996. Compositional variations in sedimentary lacustrine organic matter and their implications for high Alpine Holocene environmental changes: Lake St. Moritz, Switzerland. Organic Geochemistry 24, 453–461. Ariztegui, D., Asioli, A., Lowe, J.J., Trincardi, F., Vigliotti, L., Tamburini, F., Chondrogianni, C., Accorsi, C.A., Bandini Mazzanti, M., Mercuri, A.M., Van der Kaars, S., McKenzie, J.A., Oldfield, F., 2000. Palaeoclimate and the formation of sapropel S1: inferences from Late Quaternary lacustrine and marine sequences in the central Mediterranean region. Palaeogeography, Palaeoclimatology, Palaeoecology 158, 215–240. Ariztegui, D., Chondrogianni, C., Lami, A., Guilizzoni, P., Lafargue, E., 2001. Lacustrine organic matter and the Holocene Palaeoenvironmental record of Lake Albano (central Italy). Journal of Paleolimnology, in press. Barber, D.C., Dyke, A., Hillaire, C., Jennings, A.E., Andrews, J.T., Kerwin, M.W., Bilodeau, G., McNeely, R., Southon, J., Morehead, M.D., Gagnonm, J.-M., 1999. Forcing of the cold event of 8200 year ago by catastrophic drainage of Laurentide lakes. Nature 400, 344–348. Battarbee, R.W., 1978. Observations on the recent history of Lough Neagh and its drainage basin. Philosophical Transactions of the Royal Society of London, Series B 281, 303–345. Battarbee, R.W., 1986. Diatom analysis. In: Berglund, B.E. (Ed.), Handbook of Holocene palaeoecology and palaeohydrology. Chichester, Wiley, pp. 527–570. Battarbee, R.W., 2000. Palaeolimnological approaches to climate change, with special regard to the biological record. Quaternary Science Reviews 19, 107–124. Battarbee, R.W., Renberg, I., 1990. The surface water acidification project (SWAP) palaeolimnology programme. Philosophical Transactions of the Royal Society of London, Series B 327, 227–232. Bennion, H., 1994. A diatom-phosphorus transfer function for shallow, eutrophic ponds in south-east England. Hydrobiologia 275/276, 391–410. Bennion, H., Wunsam, S., Schmidt, R., 1995. The validation of diatom-phosphorus transfer functions: an example from Mondsee, Austria. Freshwater Biology 34, 271–283. Brugam, R.B., 1983. The relationship between fossil diatom assemblages and limnological conditions. Hydrobiologia 98, 223–225. Calanchi, N., Dinelli, E., Lucchini, F., Mordenti, A., 1996. Chemostratigraphy of late Quaternary sediments from Lake Albano and central Adriatic Sea cores (PALICLAS Project). Memorie dell’Istituto italiano di Idrobiologia 55, 247–264. Carpenter, S.R., Elser, M.M., Alser, J.J., 1986. Chlorophyll production, degradation, and sedimentation: implications for paleolimnology. Limnology and Oceanography 31, 112–124. Chiarucci, G., 1985. Materiali dell’et"a del bronzo nelle acque del Lago di Albano. Archeologia Laziale VII 11, 34–39. Chondrogianni, C., Ariztegui, D., Guilizzoni, P., Lami, A., 1996a. Lakes Albano and Nemi (central Italy): an overview. Memorie dell’Istituto italiano di Idrobiologia 55, 17–22.

Chondrogianni, C., Ariztegui, D., Niessen, F., Ohlendorf, C., Lister, G., 1996b. Late Pleistocene and Holocene sedimentation in Lake Albano and Lake Nemi (central Italy). In: Guilizzoni, P. and Oldfield, F. (Eds.), Palaeoenvironmental Analysis of Italian Crater Lake and Adriatic Sediments (PALICLAS). Memorie dell’Istituto italiano di Idrobiologia 55, pp. 23–38. D’Ancona, V., 1942. Relazione sulle ricerche idrobiologiche e idrografiche compiute nel Lago di Nemi. International Review of Hydrobiology 45, 235–264. Follieri, M., Magri, D., Narcisi, B., 1993. Palaeoenvironmental investigations on long sediment cores from volcanic lakes of Lazio (Central Italy)FAn overview. In: Negendank, J.F.W., Zolitschka, B. (Eds.), Paleolimnology of European Maar Lakes. Lecture Notes in Earth Sciences, vol. 49. Springer, Berlin, Heidelberg, pp. 95–107. Francus, P., Leroy, S., Mergeai, I., Seret, G., Wansard, G., 1993. A multidisciplinary study of the Vico Maar sequence (Latium, Italy): Part of the last cycle in the Mediterranean area. Preliminary results. In: Negendank, J.F.W. and Zolitschka, B. (Eds.), Paleolimnology of European Maar Lakes. Lecture Notes in Earth Sciences Springer-Verlag, Berlin, Heidelberg 49, pp. 129–148. Frey, G., 1974. Paleolimnology. Mitt. Internationale Vereingung Limnologie 20, 95–128. Fritz, S.C., 1989. Lake development and limnological response to prehistoric and historic land-use in Diss, Norfolk, UK. Journal of Ecology 77, 182–202. George, D.G., Harris, G.P., 1985. The effect of climate on long-term changes in the crustacean zooplankton biomass of Lake Windermere UK. Nature 316, 536–539. Guilizzoni, P., Lami, A., 1999. Palaeoclimate and anthropogenic impact on aquatic ecosystems as inferred from the analyses of natural archives. In: Farina, A. (Ed.), Perspectives in Ecology. INTECOL and SITE. Backhuys Publishers, Leiden, pp. 87–98. Guilizzoni, P., Oldfield, F., 1996. Special volume: Palaeoenvironmental analysis of Italian crater lake and Adriatic sediments (PALICLAS) Memorie dell’Istituto italiano di Idrobiologia 55, 357pp. Guilizzoni, P., Bonomi, G., Galanti, G., Ruggiu, D., 1983. Relationship between sedimentary pigments and primary production: evidence from core analyses of twelve Italian lakes. Hydrobiologia 103, 103–106. Guilizzoni, P., Lami, A., Marchetto, A., 1992. Plant pigment ratios from lake sediments as indicators of recent acidification in alpine lakes. Limnological and Oceanography 37, 1565–1569. Guilizzoni, P., Marchetto, A., Lami, A., Oldfield, F., Manca, M., Belis, C.A., Nocentini, A.M., Comoli, P., Jones, V.J., Juggins, S., Chondrogianni, C., Ariztegui, D., Lowe, J.J., Ryves, D.B., Devoy, E., Battarbee, R.W., Rolph, T.C., Massaferro, J., 2000. Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 kyr BP. Journal of Paleolimnology 23, 117–127. Hann, B.J., Leavitt, P.R., Chang, P.S.S., 1994. Cladocera community response to experimental eutrophication in Lake 227 as recorded in laminated sediments. Canadian Journal Fisheries. Aquatic Sciences 51, 2312–2321. Herzig, A., 1984. Temperature and life cycle strategies of Diaphanosoma brachyurum: an experimental study on development, growth and survival. Archiv fur . Hydrobiology 101, 143–178. Hutchinson, G.E., 1970. Ianula: An account of the history and development of the Lago di Monterosi, Latium, Italy. Transactions of the American philosophical Society 60, 178. Jeppesen, E., Madsen, E.A., Jensen, J.P., Anderson, N.J., 1996. Reconstructing the past density of planktivorous fish and trophic structure from sedimentary zooplankton fossils: a surface sediment calibration data sets from shallow lakes. Freshwater Biology 36, 115–127.

P. Guilizzoni et al. / Quaternary International 88 (2002) 57–68 Kelly, M., Huntley, B., 1991. An 11 000-year record of vegetation and environment from Lago di Martignano, Latium, Italy. Journal of Quaternary Sciences 6, 209–224. Kerfoot, W.C., 1974. Net accumulation rates and the history of cladoceran communities. Ecology 55, 51–61. Kitchell, J.A., Kitchell, J.F., 1980. Size-selective predation, light transmission, and oxygen stratification: evidence from recent sediments of manipulated lakes. Limnology and Oceanography 25, 389–402. Lami, A., Niessen, F., Guilizzoni, P., Masaferro, J., Belis, C.A., 1994. Palaeolimnological studies of the eutrophication of volcanic Lake Albano (Central Italy). Journal of Paleolimnology 10, 181–197. Lami, A., Guilizzoni, P., Bettinetti, R., Belis, C.A., Manca, M., Comoli, P., Marchetto, A., 1996. Biological records of late Pleistocene and Holocene environmental changes from two Italian crater lake sediments: results from an European interdisciplinary research project (PALICLAS). Il Quaternario, Italian Journal of Quaternary Sciences 9 (2), 711–720. Lami, A., Guilizzoni, P., Ryves, D.B., Jones, V.J., Marchetto, A., Battarbee, R.W., Belis, C.A., Bettinetti, R., Manca, M., Comoli, P., Nocentini, A.M., Langone, L., 1997. A late glacial and Holocene record of biological and environmental changes from the crater Lake Albano, central Italy: an interdisciplinary European project (PALICLAS). Water Air and Soil Pollution 99, 601–613. Leavitt, P.R., 1993. A review of factors that regulate carotenoid and chlorophyll deposition and fossil pigment abundance. Journal of Paleolimnology 9, 109–127. Leavitt, P.R., Sanford, P.R., Carpenter, S.R., Kitchell, J.F., 1994. An annual record of production, planktivory and piscivory during whole-lake manipulations. Journal of Paleolimnology 11, 133–149. Leavitt, P.R., Vinebrooke, R.D., Donald, D.B., Smol, J.P., Schindler, D.W., 1997. Past ultraviolet radiation environments in lakes derived from fossil pigments. Nature 388, 457–459. Lowe, J.J., Accorsi, C.A., Bandini Mazzanti, M., Bishop, A., van der Kaars, S., Forlani, L., Mercuri, A.M., Rivalenti, C., Torri, P., Watson, C., 1996. Pollen stratigraphy of sediment sequences from lakes Albano and Nemi (near Rome) and from the central Adriatic, spanning, the interval from oxygen isotope stage 2 to present day. Memorie dell’Istituto italiano di Idrobiologia 55, 71–98. Magri, D., 1997. Middle and Late Holocene vegetation and climate changes in peninsular Italy. In: Nuzhet . Dalfes, H., Kukla, G., Weiss, H. (Eds.), Third Millennium BC Climate Change and Old World Collapse, NATO ASI series, vol. I 49. Springer, Heidelberg, pp. 517–530. Magri, D., 1999. Late Quaternary vegetation history at Lagaccione near Lago di Bolsena (central Italy). Review of Palaeobotany and Palynology 106, 171–208. Manca, M., Comoli, P., 1996. Reconstructing population size structure in Cladocera by measuring their body remains. Memorie dell’Istituto Italiano di Idrobiologia 54, 51–57. Manca, M., Nocentini, A.M., Belis, C.A., Comoli, P., Corbella, L., 1996. Invertebrate fossil remains as indicators of late Quaternary environmental changes in Latium lakes (L. Albano and L. Nemi). Memorie dell’Istituto italiano di Idrobiologia 55, 149–176. Marchesoni, V., 1940. Il fitoplancton del Lago di Nemi prima e dopo l’abbassamento del suo livello 1923–1939. International Review Hydrobiology 40, 305–345. Martini, M.L., Giannini, L., Prati, F., Tassi, F., Capaccioni, B., Iozzelli, P., 1994. Chemical characters of crater lakes in the Azores and Italy: the anomaly of Lake Albano. Geochemical Journal 28, 173–184. Masaferro, J., Lami, A., Guilizzoni, P., Niessen, F., 1993. Record of changes in the fossil chironomids and other parameters in the volcanic Lake Nemi (central Italy). Verhandlungen internationale Vereiningung Limnologie 25, 1113–1116.

67

Mergeai, I., 1995. Mise en e! vidence d’une fluctuaction climatique d’apr"es les diatom!ees quaternaires du Maar de Vico (Italie Centrale). Vie Milieu 45, 235–241. Negendank, J.F.W., Zolitschka, B. (Eds.), 1993. Paleolimnology of European Maar Lakes. Lecture notes in Earth Sciences, vol. 49. Springer, Berlin, Heidelberg. Niessen, F., Lami, A., Guilizzoni, P., 1993. Climatic and tectonic effects on sedimentation in central Italian volcano lakes (Latium)Implications from high resolution seismic profiles. Lecture Notes in Earth sciences, 49. In: Negendank, J.F.W., Zolitschka, B. (Eds.), Paleolimnology of European Maar Lakes. Springer, Berlin, pp. 129–148. Nimmergut, A.P., Allen, J.R.M., Huntley, B., Battarbee, R.W., 1999. Submillenial environmental fluctuations during marine oxygen isotope 2: a comparative analysis of diatom and pollen evidence from Lago Grande di Monticchio, South Italy. Journal of Quaternary Science 14, 111–123. Oldfield, F., 1996. The PALICLAS project: synthesis and overview. Memorie dell’Istituto italiano Idrobiologia 55, 329–337. Oldfield, F., Accorsi, C.A., Asioli, A., Gibbs-Eggard, Z., Juggins, S., Langone, L., Rolph, T., Trincardi, F., Wolff, G., 2000. Marine cores can also provide a high resolution Late-Holocene palaeoenvironmental record: core RF 93–30 for the Adriatic Sea. Terra Nostra, 2000/7, 5th ELDP Workshop, Pallanza, Italy, pp. 82–85. Orombelli, G., Ravazzi, C., 1996. The late Glacial and early Holocene: chronology and paleoclimate. Il Quaternario, Italian Journal of Quaternary Sciences 9, 439–444. Palacios-Fest, M.R., 1994. Non-marine Ostracode Shell Chemistry from Ancient Hohokam Irrigation Canals in Central Arizona: a Paleohydrochemical Tool for the Interpretation of Prehistoric Human Occupation in the North American Southwest. Geoarcheology: An International Journal 9 (1), 1–29. Ramrath, A., Nowaczyk, N.R, Negendank, J.F.W., 1999a. Sedimentological evidence for environmental changes since 34 000 years BP from Lago di Mezzano, central Italy. Journal of Paleolimnology 21, 423–435. Ramrath, A., Zolitschka, B., Wulf, S., Negendank, J.F.W., 1999b. Late Pleistocene climatic variations as recorded in two Italian maar lakes (Lago di Mezzano, Lago Grande di Monticchio). Quaternary Science Review 18, 977–992. Ramrath, A., Sadori, L., Negendank, J.F.W., 2000. Sediments from Lago di Mezzano, central Italy: a record of Lateglacial/Holocene climatic variations and anthropogenic impact. The Holocene 10, 87–95. Rolph, T.C., Oldfield, F., van der Post, H.D., 1996. Palaeomagnetism and rock-magnetism results from Lake Albano and the central Adriatic sea (Italy). Memorie dell’Istituto italiano di Idrobiologia 55, 265–283. Ryves, D.B., Jones, V.J., Guilizzoni, P., Lami, A., Marchetto, A., Battarbee, R.W., Bettinetti, R., Devoy, E.C., 1996. Late Pleistocene and Holocene environmental changes at Lake Albano and Lake Nemi (central Italy) as indicated by algal remains. Memorie dell’Istituto italiano di Idrobiologia 55, 119–148. Sanger, J.E., 1988. Fossil pigments in paleoecology and paleolimnology. Palaeogeography Palaeoclimatology Palaeoecology 62, 343–359. Siffedine, A., Bertrand, P., Lallier-Verg"es, E., Patience, A.J., 1996. The relationship between lacustrine organic sedimentation and palaeoclimatic variations: Lac du Bouchet (Massif Central, France). Quaternary Science Review 15, 203–212. Stella, E., Ferrero, L., Margaritora, F.G., 1978. Alteration of the plankton in a much polluted lake in Central Italy (Latium), the volcanic Lake Nemi. Verhandlungen internationale Vereiningung Limnologie 20, 1049–1054. Stuiver, M., Reimer, P.J., 1993. Extended 14C data base and revised CALIB 3.0 14C age calibration program. Radiocarbon 35, 215–230.

68

P. Guilizzoni et al. / Quaternary International 88 (2002) 57–68

Swain, E.B., 1985. Measurement and interpretation of sedimentary pigments. Freshwater Biology 15, 53–75. Thouveny, N., Creer, K.M., Blunk, I., 1990. Extension of the Lac du Bouchet palaeomagnetic record over the last 120,000 years. Earth Planet Science Letters 97, 140–161. Vigliotti, L., Capotondi, L., Torii, M., 1999. Magnetic properties of sediments deposited in suboxic-anoxic environments: relationships with biological and geochemical proxies. In: Tarling, D.H., Turner, P. (Eds.), Palaeomagnetism and Diagenesis in Sediments, vol. 151. Geological Society, Special Publications, London, pp. 71–83. Vinebrooke, R.D., Hall, R.I., Leavitt, P.R., Cumming, F., 1998. Fossil pigments as indicators of phototrophic response to salinity and climate change in lakes of western Canada. Canadian Journal of Fisheries and Aquatic Science 55, 668–681.

Watts, W.A., Allen, J.R.M., Huntley, B., 1996a. Vegetation history and palaeoclimate of the last glacial period at Lago Grande di Monticchio, Southern Italy. Quaternary Science Reviews 15, 133–153. Watts, W.A., Allen, J.R.M., Huntley, B., Fritz, S.C., 1996b. Vegetation history and climate of the last 15,000 years at Laghi di Monticchio, Southern Italy. Quaternary Science Reviews 15, 113–132. Wetzel, R.G., 1975. Limnology. Saunders Co., Philadelphia, USA, 743pp. Zolitschka, B., Negendank, J.F.W., 1996. Sedimentology, dating and palaeoclimatic interpretation of a 76.3 ka record from Lago Grande di Monticchio, southern Italy. Quaternary Science Reviews 15, 101–112. Zullig, . H., 1985. Pigmente phototropher Bakterien in Seesedimenten und ihre Bedeutung fur . die Seenforschung. Schweizerische Zeitschrift fur . Hydrologie 47, 87–126.