Clay mineral and heavy metal distributions in the lower estuary of Huelva and adjacent Atlantic shelf, SW Spain

the Science of the lbtaI -nt A”-Mc-EhUUUEn-UNV.-WrYlrnMn The Science of the Total Environment 198 (1997) 181-200

Clay mineral and heavy metal distributions in the lower estuary of Huelva and adjacent Atlantic shelf, SW Spain J.C. Fernhndez Caliani”, F. Ruiz Muiioza, E. Ga16nb aDpto. Geolog’a, Facultad de Ciencias Experimentales, Univ. Huelva, 21819-Huelva bDpto. C&talogra&a y Mineralog’a, Facultad de Q&mica, Univ. Sevilla, 41071-Sevilla

Spain Spain

Received 15 November 1996; accepted 6 February 1997

Abstract The Huelva estuary, on the south-westernSpanishAtlantic coast,is an environment strongly polluted by acid mine drainage and industrial effluents. Clay mineralogy, heavy metal and particle-size distribution in estuarine and adjacent shelf sedimentshave been analyzed in order to identify the sourcesand transport pathways of the contaminatedsediments.The estuarine sedimentsconsistof detrital terrigenousminerals(illite, kaolinite, quartz, feldspars,dolomiteand heavy minerals)derived from river catchmentsand coastalerosion,with biogeniccomponents (calcite and aragonite)and minor authigenicminerals(pyrite and possiblygypsum).Mineral distribution pattern in the estuary-shelfsystemis controlled by grain-sizesediment,physico-chemicalconditions of waters and hydrodynamicfactors. Important proportions of fine-grained sedimentshighly enriched in sulphide-associated heavy metals are suppliedby the Tinto-Odiel river system.Most of these sedimentsare trapped when river waters reach the estuarybecauseof flocculation processes during estuarinemixing, thus the estuary actsasa storagebasinfor metallic pollutants. In terms of public health, this estuary is well above recommendedsafety guidelinesfor most metals. Although the shelf sedimentsshow metal concentration levels close to background values, eventually, a metallic plumeemergesfrom the estuaryto ocean,and consequentlyelevatedmetal concentrationscan be locally detected on the inner shelf. 0 1997Elsevier ScienceB.V. Keywords:

Clay minerals;

Heavy metals; Estuary-shelf

1. Introduction Estuaries are zones of complex interaction

between fluvial and marine processes that may act as a geochemical trap for heavy metals bonded in the fine-grained sediments. In these coastal systems, mixing of continental fresh and marine salt waters usually leads to flocculation and accumulation processes of suspended sediments (e.g. FGrstner, 1983), which are controlled by some 0048-9697/97/$17.00 PI1

SOO48-9697(97)

system; Huelva; South-western

physico-chemical properties of clay minerals, such as specific surface and exchange capacity. Therefore, clay minerals play a key role as natural tracers to control the transport pathways and dispersal patterns of pollutants in the mtuarine environment (e.g. Veniale and Setti, 1991; ZSllmer and Irion, 1993). The Huelva estuary, on the south-western coast of Spain, is one of the most polluted aqueous environments in Europe as a result of the effects

0 1997 Elsevier Science B.V. All rights reserved. 05450-8

Spanish coast

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derived from acid mine drainage and disposal of industrial processing wastes, and for this reason it is one particularly interesting area for the study of interaction mechanisms between clay minerals, toxic metals, organic pollutants and living organisms. During the past decade, a large number of investigations on the Huelva coastline estuaries have been reported, especially those dealing with the sedimentary processes and products (Borrego et al., 1993, 19951, coastal dynamics and Holocene evolution (Dabrio and Polo, 1987; Rodriguez Vidal, 1987; Flor, 1990), as well as heavy metal pollution (Perez et al., 1991; Cabrera et al., 1992; Nelson and Lamothe, 1993; Elbaz-Poulichet and Leblanc, 1996) and biological response (Ruiz Muiioz et al., 1994; Gonzalez-Regalado et al., 1996; Usero et al., 1996). Nevertheless, no detailed mineralogical study has been performed to date. Thus, pollutant behaviour in the Huelva estuary has been only described on the basis of chemical considerations, but not taking into account the mineral nature of sediments. Moreover, this general lack of knowledge regarding mineralogy, in particular on clay minerals, represents a serious problem to understanding the interrelationships of estuarine and continental shelf sedimentation. This paper is concerned with the determination of the mineral composition and heavy metal content of the surface sediments and their distribution in the Huelva estuary-shelf system, in order to identify the source and transport pathways of the contaminated sediments.

198 (1997)

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Huelva harbour. Because of this, it displays an asymmetric transverse section in which the average depth ranges between 6 and 12 m (Borrego, 1992). In 1980 a long bank was built at the entrance of the estuary in order to prevent the silting of the dredged ship channel. The adjacent continental shelf is a large shoal area with a very flat bottom topography gently seaward-sloping as far as 25 m isobath (Ojeda, 1988). Tidal regime, wave action and fluvial discharge are the most salient factors controlling the hydrodynamic processes in the estuary. The tidal regime is mesotidal and semi-diurnal, with a low diurnal inequality (Borrego et al., 1993). Dominant waves come from the south-west, associated with the Atlantic circulation regime; and the sediment discharge of the Tinto-Odiel river system varies seasonally reaching a maximum between December and January, when rainfalls are abundant on the catchments. Most of the physical and chemical parameters of water, i.e. salinity, temperature, dissolved oxygen and pH values, undergo significant seasonal variations (IEO, 1992; AMA, 1993). Thus, during the summer, salinity is nearly constant at 36%0, owing to the strong tidal current effect; water temperature is about 26°C near surface water; dissolved oxygen content varies from 4 to 6 mg/I, and the pH values range between 6 and 8. In winter, partial stratification occurs where Tinto and Odiel rivers meet, and consequently the surface layer of the water column is markedly less saline (even 5%o) and more acidic (pH = 2-5) than the bottom layer (salinity = 29-32%0 and pH = 5-7).

2. The study area 2.2. Environmental 2. I. Physiographical

and hydrodynamic

framework

features

The Huelva estuary is located on the southern Spanish Atlantic coast, at the junction of the Tinto and Odiel rivers (Fig. 11, forming a wide drowned valley system incised into a Neogene detrital basement, and bordered by extensive salt marshes. In its lower part, it forms an elongateshaped coastal indentation whose main access channel, so-called Padre Santo channel, is regularly dredged to keep open the shipping to the

The Tinto and Odiel rivers discharge into the Huelva estuary after flowing through the Iberian Pyrite Belt draining volcanic-sedimentary formations of Paleozoic age (Schermerhorn, 1971), in which large deposits of polymetallic massive sulphide are interbedded. Because of the large scale mining and smelting operations that have occurred since prehistoric times on the river banks, especially at the Rio Tinto mining district, waters are very acidic and sediments are extremely pol-

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183

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LEGEND Neogene-Quaternary

sediments

Salt marshes m

Industrial

m

Phosphogypsum

,j(y

lsobaths (in metres)

0

Sampling

areas

ATLANTIC OCEAN

stacks

5Km

stations

Fig. 1. Generalized map of the Huelva

estuary

and

adjacent

luted by suiphide-associated heavy metals (Requena et al., 1991; Fernhndez Caliani et al., 1996). Consequently, sediments trapped in the estuary are highly contaminated by acid mine drainage. In addition, since industrialization began in the mid-1960s, large amounts of wastes and pollutant effluents have been also discharged from a variety of chemical factories (phosphate fertilizer plants, chloro-alkali industries) and petroleum refineries located around the estuary, Over 2-3 million tonnes of phosphogypsum by-product and 0.8 million tonnes of pyrite cinders are produced an1989); these nually from these industries (AMA, are stockpiled on the river banks, thus increasing the environmental impact of metals derived from mining activities. As a consequence of both acid mine drainage and industrial wastes dumping, estuarine sediments contain concentration levels of toxic metals

Atlantic shelf, showing the location of the sampling stations

as high as (in ppm dry wt.): 4500-6300 Cu; 2600-5100 Zn; 1900-3400 As; 1700-10400 Pb; 200-700 Mn; 9-39 Cd: and 15-49 Hg, in accordance with data of Pt5rez et al. (1991), Cabrera et (1993). Alal. (1992), and Nelson and Lamothe though it is difficult to distinguish between pollution resulting from mining activities and contamination from an industrial origin, Serrano et al. (1995) estimated that the concentration of heavy metals in the Huelva estuary has the following provenance: 83.4% is supplied by the acid mine drainage; 16.5% has an industrial origin; and 0.1% has its source in the urban effluents. The proportion of trace metals readily available for living organisms and their later effects are not well known, but some important trends have been detected. In spring and summer the a-chlorophyll can reach 180 mg/m3 because of the massive development of phytoplankton, a typical compo-

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nent of highly polluted waters (IEO, 1992). On the other hand, biocoenosis of some microfaune group, namely Ostracoda and Foraminiferida, only inhabits in the distributary channels and restricted salt marshes, i.e. those estuarine subenvironments that are protected from the metal pollution (Ruiz Muiioz et al., 1994; Gonzhlez-Regalado et al., 1996). Furthermore, the environmental impact of metals have a negative economic consequence on the region. In February 1993, the concentration of 0.1 (25-45 ppm) in soft tissues of the commercial bivalve Chamelea gallina exceeded the maximum Cu level allowed in Spain (20 ppm) for human consumption (User0 et al., 19961, which caused a temporary closure of collection and sale of bivalves. The Huelva estuary is nowadays subjected to a corrective plan for control of industrial waste disposal, with the purpose of improvement of environmental quality in this area. 3. Methodology

Particle-size distribution as well as mineralogical and chemical analyses were performed on 17 samples of bottom sediments collected with a sediment-grab of the Van Veen type, at the marine-dominated portion of the Huelva estuary and adjacent continental shelf as far as 25 m water depth. Sampling was limited to the top 10 cm of sediment. Location of sampling stations is shown in Fig. I. Sediment samples were passed through a 63 pm ASTM nylon sieve in order to separate the fine fraction from the bulk sample. The grain-size distribution was determined by sieving for particles greater that 63 pm, whereas the silt and clay fractions were obtained by means of a Coulter Counter equipment, using a lOO-pm tube. Mineral compositions of bulk sample and clay fraction were determined by X-ray diffraction on a Philips powder diffractometer equipped with an automatic slit, using nickel-filtered Cu-K LYradiation at 20 mA, 40 kV, and a scanning speed of 1” 10/min. For clay mineral analysis, the < 2 pm fraction was separated by centrifugation, and well-oriented aggregates were prepared by sedimentation of clay suspension on glass slides. Sedi-

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ment samples were pre-treated with hydrogen peroxide to eliminate the organic matter and with acetic acid to remove the carbonates. Identification of the clay minerals was carried out following the routine procedures, which involved the standard treatments of solvation with ethylene glycol and dimethylsulfoxide, and heating at 550°C. The relative abundance of the mineral phases present in both bulk sample and clay fraction was calculated by measuring the intensity of diagnostic diffraction peaks (Schultz, 1964; Martin Pozas et al., 1969; Pozzuoli et al., 1972). Heavy minerals were concentrated by gravity separation using bromoform as high-density liquid. Magnetic separation by means of a Fran& isodynamic separator was carried out on heavy mineral fraction in order to segregate diamagnetic, paramagnetic and ferromagnetic species on the basis of their different magnetic susceptibilities, for the purpose of assisting mineral identification under the binocular microscope. Additional techniques were employed, such as X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy, to obtain information on textural features and chemical composition, thus allowing more accuracy of heavy mineral analysis. Chemical analysis for heavy metals in sediment were performed on the bulk samples by X-Ray Assay Laboratories, Toronto (Canada). Metal concentrations were determined by X-ray fluorescence spectrometry (Cu, Pb, Zn, Cr and Ni) and atomic absorption spectrometry (Cd, As and Hg), using the cold-vapor technique for Hg determination. Metal pollution assessment from sediment analysis was based on the geoaccumulation index (Miiller, 19811, taking into consideration the averages of uncontaminated sediment samples from the Huelva littoral (Ruiz Muiioz, 1995) as background values for reference. Finally, a statistical study of the granulometric, mineralogical and chemical data set was accomplished by multivariate analysis in order to evaluate the interrelationships among the most representative variables. In a previous step to mathematical treatment, data were standardized, i.e. each variable accounts a mean of zero and it is expressed in units of standard deviation

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(Reyment and Joreskog, 1993). The next step is to calculate the Pearson linear correlation matrix. A principal component analysis was then applied using the sub-program Factor of the Statistical Package for the Social Sciences. Factor loadings up to 10.41were recovered from statistical analysis. At the same time, the samples were divided into a predetermined number of groups by a quick clusTable 1 Granulometric Samples

1 2 3 4 s 6 7 8 Y 10

11 12 13

Gravel

Sand

(GR)

Very coarse WCS) -

2.85 0.11

1.22 6.58

Samples

Depth (m)

11 12 13 14 1s 16 17

0.56 0.55 6.75 3.65 9.46 6.58 6.38 1.62 3.40 5.33 2.52 2.x7 0.51 5.26

9.69 0.92 42.18 8.03 14.88 1.09 7.54 2.06

0.69 10.44 2.00 17.54 18.54

1 5 6 7 3 9 10

I8I-200

185

ter analysis (Anderberg, 19731, using the Euclidean distance as a similarity measure. 4. Sediment size distribution Textural features of the sediments change noticeably in the marine portion of the estuary. Indeed, at the junction of the Tinto and Odiel

data and textural parameters of sediment samples

1-l IS 16 17

1 2 3

I98 (1997)

2.10 18.13 21.97

-

__ Coarse (CS)

(MS)

Medium

Fine (FS)

Very fine WFS)

2.34 0.54 12.32 7.05 9.46 19.65 I 2.0% 3.55 2.75 9.30 4.98 1.60 1.62 8.76 6.34 18.31 23.95

4.74 2.42 31.28 22.43 33.35 63.58 39.35 25.83 12.12 20.45 20.49 3.76 7.58 57.91 12.90 38.98 19.53

15.32 4.74 19.51 18.04 5.31 2.76 26.55 35.23 31.45 34.19 40.52 19.32 74.11 11.96 32.63 5.90 6.75

18.41 5.12 7.26 5.52 0.17 0.06 0.48 28.78 39.71 15.97 24.28 34.05 15.26 6.03 39.09 0.72 4.67

Grain size mean (0)

12 9

4.00 4.20

14 12.8 13.7 10.9 1.3 7.3 7.3 12.8 16.4 16.3 5.5 x5 s.5 17 23

1.10 1.80 -0.45 0.80 1.22 2.22 2.60 2.20 2.30 2.10

2.10 2.05 2.05 0.45 -0.16

S.D. 1.70 1.19 1.84 1.54 2.31 0.57 1.28 0.94 1.76 1.29 0.99 1.96 0.57 0.92 0.84 2.01 2.05

_-~ Clay

Silt Coarse

(CST) 7.57

11.17 2.93 13.84 0.00 0.00 0.00 1.07 0.88 5.55 1.57 9.78 0.04 0.00 0.71 0.01 1.89

Medium (MST)

Fine (FST)

Very fine WFST)

11.24 20.96 2.74 9.63 0.00 0.00 0.00 1.04 0.60 3.90 1.91 8.99 0.03 0.00 1.86 0.08

15.20 23.18

13.58

1.01

Sorting (So) 1.95

1.00 1.67 1.45 2.70 0.60 1.02 1.02 1.40 1.03 1.02 1.75 0.45 0.75 0.72 1.97 1.75

2.60 9.63 0.00 0.00 0.00 1.30 1.13 1.93 1.78 6.64

0.11 0.00 1.54 0.23 0.84

Kurtosis 0.66 0.87 1.32 1.26 0.59 1.61 1.27 0.85 1.57 1.59 1.12 1.19 1.57 1.54 1.29 1.18 1.53

20.99 0.97 6.10 0.00 0.00 0.00 0.23 0.28 0.91 0.52 4.02 0.03

(CL) -8.18 10.23 3.27 3.46 0.00 0.00 0.00 0.26 0.14 0.39 0.21 2.40

0.00

0.01 0.00

0.50 0.05 0.47

0.32 0.03 0.38

--.-

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rivers the channel facies consist mainly of black silty muds, whose mean grain size ranges from 4 to 4.2 0, with burrows filled by fine and very fine sands (Table 1). The particle size increases seaward along the Padre Santa channel. Thus, in the estuary mouth, medium-grained sand bodies occur with gravel deposits formed by abundant shell fragments of Mollusca (Charnellea gullina, Donax uittatus, Spisula elliptica, Bittium reticulaturn), whereas silty and clayey sediments are absent. At the entrance of the estuary the natural distribution of the sediments is strongly affected by dredging. Moreover, since the construction of the bank, medium and fine sands were deposited on its outer side by wave action, leading to the development of recent sandy beaches. Although the sediment size distribution in the adjacent continental shelf is more homogeneous than in the estuary, some textural variations can be distinguished. For instance, the shelf sediments sampled at the Mazag6n sector are composed mainly of medium to very fine sands. Silt percentages increase at the same time with both the depth of water and distance to the estuary mouth, but also some lag deposits can be found locally. At the Punta Umbria area, granulometric differences have also been detected in the shelf sediment distribution with depth. Thus, in shallow marine sediments, fine-grained sands with scattered shell fragments are clearly dominant, however, medium-grained sands with numerous shells of Bivalvia (Charnellea gallina, Spisula elliptica, G&z,vmelys glycymevs) and Scaphopoda (Dentalium vulgare) occur in the deeper shelf sediments. In as much as the textural parameters of sediments, sorting values vary between 0.45 and 2.7 indicating a polymodal distribution of the grain size. Most of the samples are badly or very badly sorted (s,, > l.O), especially those collected from the estuary and deep sea. Moderate to well sorted sands (s,, < 0.75) solely occur in the coastal marine sediments from the Punta Umbria area, and locally at the seaward end of the Padre Santo channel. The Kurtosis parameter averages 1.2, although it crin reach values as low as 0.6 in some cstuarine

sdiments.

198 (1997) 181-200

5. Mineralogy of sediments

5.1. Bulk sample The mineral whole composition of most of the studied samples consists mainly of quartz, feldspars, carbonates and phyllosilicates. Besides these, gypsum as well as poorly crystallized mineral phases (oxi-hydroxides of iron) are present in some samples. From the mineral distribution on the estuary and adjoining shelf (Fig. 2) it may be seen that the estuarine sediments are largely enriched in phyllosilicates (> 50 wt. % of the bulk sample) as compared to quartz (28-32%) and feldspars (7-10%). The phyllosilicates/quartz + feldspars ratio is dramatically inverted along the Padre Santo channel, in such a way that the marine sediments are clearly dominated by quartz, feldspars and carbonates, with the exception of the deeper samples collected from the continental shelf (namely 11, 12 and 171, in which clay minerals are again dominant (36-38%) as compared to quartz (27-14%). The greatest concentrations of quartz were detected at the seaward end of the channel, where it can reach relative proportions as high as 90% of the whole sediment. Feldspars (both Na-rich plagioclase and alkaline feldspar) appear in varying percentages in all studied samples. Carbonate minerals consist of calcite, aragonite and dolomite, in this order of abundance, although aragonite is more abundant than calcite in some cases. The carbonate content ranges between 10 and 30% in the shelf sediments, whereas small amounts of carbonates (less than 10%) were found in the outer estuary. It is interesting to note the lack of carbonates at the confluence of the Odiel and Tinto rivers. Subordinate amounts of gypsum and hematite can also be present in this estuary-shelf system. 5.2. Clay fraction ( < 2 pm) Clay minerals distribution in the < 2 pm fraction of sediments of the lower estuary and adjacent continental shelf is shown in Fig. 3. Because

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I98 (I997)

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I87

Fig. 2. Mineral composition of the bulk sample of sediments. Key: 1: Quartz; 2: Phyllosilicates; 3: Carbonates; 4: Feldspars; 5: Others (gypsum, oxi-hydroxides of iron, heavy-minerals).

of the scarcity of the clay fraction in shallow marine sediments, some samples from the near shore have not been depicted in maps. The estuarine clay assemblage is very simple and monotonous, and consists of illite and kaolinite, while chlorite can appear as an accessory phase in the fine fraction of the shelf sediments. There was a generalized lack of smectites in all samples. Illite is by far the most abundant clay mineral in both estuary and shelf sediments. It comprises over 70% of the estuarine clays, increasing its relative abundance up to 80% in marine sediments. According to the ratio of the (002) and (001) basal reflections, which range from 0.58 to 0.75, they are dioctahedral micas corresponding to the 2Ml polytype. The illite crystallinity, measured by the width of the peak at half-height of the first basal reflection on X-ray diffractograms,

vary between 0.22 and 0.29” A 20, by which they are well-crystallized micas. Since there are little or negligible variations in crystal chemistry parameters of micas (basal spacing, crystallinity index) from the estuary compared to those from the continental shelf, the mineralogical differences are mainly quantitative. Kaolinites are present in significant quantities ranging from 1536%. Samples with higher kaolinite contents (26-36%) are found in the estuary. In general, it seems that the relative proportions of kaolinite decreases gradually seaward as opposed to iliite (Fig. 4). Kaolinites show a low degree of crystalline order, their crystallinity indices greater than 0.5 (index of Amigo et al., 1994). They also have a low swelling capacity upon DMSO treatment. The percentage of swelling kaolinite, calculated by comparison of

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Fig. 3. Clay mineral distribution in the < 2 pm fraction of sediments. Key: 1: Mite; 2: Chlorite; 3: Kaolinite.

the area of the basal reflection at 7 A before and after the treatment is relatively moderate (46-64%). Finally, chlorite is only present in subordinate amounts (< 5%) in the marine sediments, and it never appears in the estuarine sediments. 5.3. Heaq fiaction

Heavy mineral fraction represents only less than 5% wt. of the bulk sample, but it is composed of a wide spectrum of mineral species which are mostly concentrated in the fine to medium sand-size sediments. The most common high-density accessory minerals found in sediment samples (Table 3) are oxides, hydroxides and sulphides of iron (magnetite, limonite. hematite, goethite and pyrite 1, titanium-bearing minerals (ilmenite, ru-

tile, anatase and sphene), as well as a variety of transparent minerals such as andalusite, apatite, baryte, epidote, garnet, green hornblende, muscovite, tourmaline and zircon. These results are in agreement with a preliminary study on the heavy minerals of the Huelva littoral reported by the Spanish Geological Survey (IGME, 1974). Some mineralogical and textural differences have been recognized between estuarine and coastal sediments in terms of their heavy mineral content. The latter are often enriched in ilmenite, and show a high mineralogical maturity as evidenced by the relative frequency of ultrastable minerals such as zircon, tourmaline and rutile, which are characterized by their resistance to physical and chemical degradation. In contrast, the estuarine heavy mineral association comprises framboids of microcrystalline pyrite (Fig. .5), the

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189

Atlantic Ocean Fig. 4. Illite/Kaolinite

ratio in the < 2 pm fraction of sediments.

weathering products of iron sulphide orebodies (limonite, hematite, goethite) and detrital grains of typically metamorphic minerals. It is interesting to note the presence of well preserved crystals of amphiboles and zircon with extensive rounding (Fig. 6) in th e h eavy fraction of estuarine sediments, indicating two contrasting sediment derivation paths. 6. Heavy metal content Analytical data of heavy metals in the estuary and shelf sediment samples are listed in Table 3 together with their indices of geoaccumulation. Heavy metal content varies a lot depending on the location of the sampling stations. By far, the greatest concentrations of metallic pollutants were

found in the estuary, especially where the Odiel and Tinto rivers join. In this area, sulphide-associated metals reach values as high as follows (in ppm): 1830 Cu; 926 Pb; 2300 Zn; and 850 As. These values exceed by more than one order of magnitude the natural background levels, which involves indices of geoaccumulation corresponding to strongly polluted sediments. Important anomalies were also detected for the rest of the analyzed trace metals (150 ppm Cr; 46 ppm Ni; 9 ppm Cd; and 11.6 ppm Hg). Sediment contamination by heavy metals declines significantly along the Padre Santo channel in a seaward direction, although relatively high values (421 ppm Cu; 295 ppm Pb; 592 ppm Zn; and 259 ppm As) occur again near the estuary mouth. Otherwise, the much lower concentrations

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Table 2 Relative abundance of heavy minerals in estuary and shelf sediments Heavy mineral Estuary sediments Shelf sediments Anatase Andalusite Apatite Baryte Epidote Garnet Goethite Hematite Hornblende Ilmenite Limonite Magnetite Muscovite qriite Rut& Sphene Tourmaline Zircon

l

l -

l

l

me

l l e -

l l l

e

l

l

ee

*a

l

e

l

l

*

0

l

e

me

-

ee

l

l

l e

l

l

l

a* e

7.2. Cluster analysis

e

a*

____.-.

Key: -, dant.

no detected;

l

, scarce;

l

l

, common;

l

l

l

, abun-

were found in the shelf sediments from the Punta Urnbria area. Here, metal concentrations are close to background values. Fig. 7 displays the spatial distribution of copper, lead and zinc in sediments of the study area. In general, all the heavy metals show a similar distribution pattern. 7. Statistica

coarser particle sizes (gravel to medium sand), quartz and carbonates. Factor 2 is dominated by gravel to medium-grained sand sediment sizes, with a minor contribution by quartz, whereas fine and very fine sands show high negative contributions. The first and the second factors accounted for 75% of the total variance, and consequently a bivariate plot using these factors (Fig. 8) explains most of the information. Accordingly factor 3, only carbonates and very coarse sands have moderate positive scores, with negative contributions by quartz and medium sands. Therefore, very coarse sands and gravels are mainly composed of shell fragments.

l

l e

l

198 (1997) 1X1-200

treatment

of data

7.1. Correlation matrix and principal component ana&sis

Structure of the variable dependence was found by Pearson correlation matrix (Table 4) and principal component analysis. In this way, three factors were extracted which accounted for 83% of the total variance (Table 51. Factor 1 is characterized by very high positive contributions (loadings up too.791 for heavy metals, tine grain-size fractions and phyllosilicate percentages. All these variables have significant correlation coefticients among themselves. On the other hand. negative loadings were recovered for

On the basis of particle-size distribution, mineralogical composition and heavy metal content, four statistical significant sample groups can be predetermined for both estuary and shelf sediments, which are depicted on the Huelva littoral map (Fig. 9). Table 6 summarizes the metal pollution assessment for each cluster on the basis of the geoaccumulation index ( I,,, 1. Cluster 1 includes the silty-clayey sediments sampled at the junction of the Tinto and Odiel rivers, in which phyllosilicates dominate over quartz, and carbonates are absent. These samples contain a large amount of all the metal pollutants, except for Cr and Ni. Cluster 2 covers two areas containing moderately to strongly polluted sediments, which are characterized by the presence of carbonates. Cluster 3 spreads over a zone located in both fluvial and marine side of the Huelva bank. This group comprises unpolluted sediment samples with high percentages of quartz-rich medium sands and very low phyllosilicate content. Carbonates are moderately abundant, with a calcite/aragonite ratio > 1 if juvenile shells are dominant and < 1 if adult forms prevail. Cluster 4 is confined to Punta Umbria area and the south-eastern part of Mazagon. In these sediments quartz generally dominates over phyllosilicates, carbonates are relatively abundant, and heavy metal average is variable, being

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198 (19973 181-200

191

Fig. 5. SEM photomicrograph showing a framboid of microcristalline pyrite, from estuarine sediments.

Fig. 6. SEM view of heavy minerals (A: amphibol; Z: zircon; and H: hematite) with contrasting textural features, from estuarine sediments.

Back ground

9 10 11 12 13 14 1.5 16 17

8

Samples

Table 3 c-onccntration

21.7

1800 1830 512 936 22 362 24 77 74 421 177 108 35 17 < 10 23 95

Cu

< < <

<

<

I,,*

(values

0.00

5.76 5.79 3.95 4.82 0.00 3.45 0.00 1.22 I.16 3.67 2.42 1.71 0.08 0.00 0.00 0.00 1.52

Cu

reported

23.6

926 800 261 400 31 35 30 90 69 29.5 105 90 23 12 < 10 20 127

Pb

0.00

4.68 4.47 2.86 3.47 < 0.00 0.08
2300 1960 828 1400 75 102 97 278 233 592 375 272 186 61 62 74 206

Zn

index

< < <

< < <

0.00

3.88 3.65 2.41 3.17 0.00 0.00 0.00 0.83 0.58 1.92 1.27 0.80 0.25 0.00 0.00 0.00 0.40

lgeo Zn

and geoaccumulation

lgco Pb

in ppm)

17.1

150 110 35 66 < 10 < 10 < 10 45 35 51 33 40 25 < 10 16 < 10 18

Cr

< < < < <

< < <

I,,,

0.00

2.56 2.11 0.46 1.37 0.00 0.00 0.00 0.82 0.46 1.00 0.37 0.65 0.00 0.00 0.00 0.00 0.00

Cr

UaeO ) of heavy

< < < < < <

< < < < <

i

2.62 1.68 <0.41 0.55 co.41 co.41 <0.41 < 0.41 co.41 1.00 < 0.42 < 0.41 < 0.41 co.41 co.41 co.41 0.41 0.00

5

lgea Ni

in sediment

46 24 10 11 10 10 10 10 10 15 10 10 10 10 10 10 10

Ni

metals

29.7

850 710 300 420 22 25 35 154 54 259 70 39 12 19 12 31 60

As

samples.

< < < <

< <

I,,,

0.00

4.62 4.36 3.12 3.61 0.00 0.00 0.00 2.16 0.65 2.91 1.02 0.18 0.00 0.00 0.00 0.00 0.80

As

(Background




<1 <1
0.5

1

1

2

1

9 7 2 3

Cd

values

< < <

< <

<

< < <

0.00

3.58 3.22 1.41 2.00 0.41 0.41 0.41 0.41 0.41 1.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41

&.o Cd

from

Ruiz

0.1

11.6 6.7 2.5 5.4 < 0.1 < 0.1 0.1 0.3 0.4 1.3 0.9 0.6 < 0.1 < 0.1 < 0.1 0.1 0.8

&

Muiioz

Hs

0.00

6.27 5.48 4.06 5.17
&v

(1995))

J.C. Femdndez

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et al. / The Science of the Total Environment

198 (1997) 181-200

193

7 Punta Umbna

Fig. 7. Spatial variation in the concentrations of sulphide-associated metals.

the sediments located near Mazagon beach (cluster 4B) more polluted that those sampled in the vicinity of Punta Umbria area (cluster 4A). 8. Discussion and conclusions The mineral composition of the black silty muds found in the estuary correspond more closely to particulate matter suspended in the Tinto river (Fernandez Caliani et al., 1996; Galan et al., 1996) than to shelf sediments. The clay mineral assemblage (illite and kaolinite) and accompanying non-clay species (quartz and feldspars) of the estuary are in good agreement with a riverine source, and so it can be generalized that most of the sedimentary load arriving in the estuary consists of silty and clayey sediments carried in suspension by rivers. The sediments supplied by the Tinto-Odiel system are composed of detrital minerals that were originally formed on the continent and subsequently derived from the rocks and soils, drained, and then subjected to river water erosion. Thus, well-crystallized micas have their

source area in the Paleozoic crystalline basement that contains the large ore deposits of the Iberian Pyrite Belt (Fernandez Caliani and Galan, 19911, and disordered kaolinite is a residual weathering product of the acid volcanoclastic rocks that constitutes the host of the sulphide masses (Poyato et al., 1981). In addition, some heavy minerals found in the lower estuary, particularly green hornblende, are present as rock-forming minerals occurring in the river catchments (Requena et al., 1991). Although an important proportion of sediments supplied by rivers is trapped in the estuary and never reaches the continental shelf, during severe flood stages the river sediment load can be transported directly to the ocean through the Padre Santo channel. In this case, illite and kaolinite are the major clay minerals being carried to the marine environment. It is evident from the spatial distribution of kaolinite in sediments that clay mineral segregation by flocculation and differential settling occurred on the estuary mouth. Since kaolinite settles preferentially in the estuarine sediments (Weaver, 19891, the illite/kaolinite

1 .oo

0.15

0.39

-0.36 -0.35 -0.39 -0.47 -0.25 -0.36 -0.32 -0.32

-0.35 -0.32 -0.37 -0.47 -0.24 -0.35 -0.33 -0.32

-0.33 -0.35 -0.39 -0.53 -0.28 -0.36 -0.36 -0.34

0.93

0.98

0.96

1.00

MST

0.97

1.00 0.99

CST

-0.39 -0.48 -0.47 -0.61 -0.43 -0.43 -0.46 -0.43

-0.29 0.24 -0.20 -0.06 -0.20 -0.23 -0.21 -0.23 0.72 0.52

-0.15 -0.04 -0.08

0.77

0.83 0.81

0.82 0.67

0.85

0.87 0.85

CAR,

0.85

0.89 0.89

0.88 0.75

0.90

0.93 0.91

-0.10 -0.02 0.71 0.69 -0.49 -____ -0.53

phyllosilicates;

0.68

0.70 0.63

0.76

-0.01

-0.10 -0.10

0.72 0.71

-0.16 -0.09

0.28 -0.19 0.22 0.76 0.12 -0.41

0.80 -0.20 -0.47 -0.57 -0.49 -0.45

-0.20

0.12 0.15 0.27 0.17 0.14 -0.52 -0.31 -0.39 -0.67 0.05 0.48 0.56 0.29 0.08 -0.04 -

0.40

-0.50

P < 0.01 for coefficients in bold type. P < 0.05 for underlined coefficients. Abbreuiutiom: Q, quartz; FEL, feldspars; PHY, Textural abbreviations are given in Table 1.

Hg

Cd

As

Pb Zn Cr Ni

cu

Q FEL PHY CAR

-0.44 0.73

0.74

-0.35

-0.08

-0.32 -0.35 -0.41 -0.49 -0.30 -0.08

-0.33

-0.20 -0.26

0.81

-0.51 -0.56

-0.37 -0.39 -0.47 -0.54 -0.28 -0.03

-0.39 -0.47

FST VFST CL

-0.32 -0.39

1.00 0.87

1.00

CST

0.03 0.00

1.00

0.49

VFS

-0.40 -0.39

1.00 0.30

MF

CST MST

0.64 0.41

0.36 0.40

- 0.49 - 0.60 -0.56

1.00

1.00 0.87

MS

-0.47

0.62 0.48 0.38 0.46

vcs

matrix ___~_-_cs

VFS

FS

MS

C‘S

GR VCS

GK

l~ablc -I Pearson correlation

-0.44

1.0

CL

0.95 0.94 0.94 0.89 0.80 0.93 0.93 0.89

-0.59

0.72

-0.02

carbonates.

0.93 0.91 0.89 0.86 0.78 0.88 0.90 0.84

-0.53

0.62

-0.01

-0.37

0.97

1.00

VFST

-0.01

-0.49 -0.01 -0.56 0.07 -0.33 0.06 -0.46 0.06 -0.38 0.04 -0.43 0.04

-0.46

PHY

1.00

CAR

0.77 --0.54 0.74 0.65 0.78

0.73 0.77

-0.63 -0.55 -0.71 -0.65 -0.62

-0.67 -0.68

0.69 -0.72

1.00 0.15 -0.52

0.06

1.00

FEL

-0.35 -0.05

0.09

0.05

1.00 -0.17

Q

0.96 0.92 0.99 0.98 0.97

0.87 0.97 0.97 0.95

1.00 0.99

Pb

0.98 0.98 0.91

Cu

0.87 0.99 0.96 0.98

1.00

0.95

Zn

Ni

0.94 0.93

0.91 1.00 0.95 0.90 0.95 0.95

1.00

Cr

0.97

1.00 0.98

As

0.96

1.00

Cd

1.00

Hg

5 c? 8

2

2 3

ii ;: s

4. 3

2. 3” 2 % 2 oy iJ

t

-.s R R

3a R 0 B

3

;

P

J. C. Fern&de2

Caliani

et al. / The Science of the Total Environment

Table 5 Variable loadings on the first three factors from a principal component analysis of sediment texture, mineral and chemical composition data. (loadings below 0.4 have been omitted) Variables

Factor 1

Factor 2

GR vcs cs MS FS VFS CST MST FST VFST CL

-0.469 - 0.459 - 0.507 - 0.591

0.546 0.612 0.701 0.578 - 0.820 - 0.864

Q FEL PHY CAR

- 0.553

-

CU Pb Zn Cr Ni As Cd Hg % Total variance ----__

Factor 3 0.560 - 0.436

0.796 0.914 0.948 0.930 0.955 0.460

0.804 - 0.660

- 0.602 0.595

0.960 0.973 0.978 0.972 0.856 0.966 0.950 0.939 60.04

15.54

7.03

ratio increases seaward indicating effective transport and dispersion of illite by river flow. Therefore, the illite/kaolinite ratio identifies the advective plume that emerge from the estuary to the shelf Bowing parallel to the coast (Palanques et al., 1987), and consequently the pathways by which the inputs of suspended sediments escape to the open sea could be inferred from the clay mineral distribution. Similar patterns have been also observed in other estuaries which are river dominated (e.g. Edzwald and O’Melia, 1975; Feuillet and Fleischer, 1980). The nature and distribution of clay minerals on the continental shelf suggests dilution of the riverine clay mineral assemblage, enriched in illite and kaolinite, by a marine suite characterized by the presence of chlorite, with a relative high

198 (1997)

181-200

195

content of illite and lesser amounts of kaolinite. This trend has been also detected in the outer shelf (Palanques op. cit.), where the sediments have more chlorite and less kaolinite than in the inner shelf. So far we have assumed that the Tinto and Odiel rivers are the major contributors of continental sediments to the ocean, but also the Huelva estuary can work as a trap for sediments derived from coastal erosion. Despite the supply of marine sediments, it is partially made worse by the bank which is built at the entrance of the Padre Santo channel. Here There is evidence of shelfsediment transport into the estuary, especially during high tidal periods. Thus, much of the biogenie components (calcite and aragonite) are supplied to the estuary mouth from the ocean by tidal currents. The influx of sediments entering the estuary from the ocean is also seen by some heavy minerals such as ilmenite or magnetite, which are common products of erosion of the Huelva shoreline. This suggests that the estuarine sediments, mainly fluvial in origin, are admixed with a variable proportion of coastal marine material, depending on the tidal energy. Although most of the estuarine mineralogical components resulted from the mixing of river and marine sources, it must be pointed out that the occurrence of authigenic iron sulphides formed directly in the estuary. Finally, the presence of gypsum in shelf sediments could be explained either as an authigenic mineral formed by the reaction of the carbonate biogenic material with acid sulphate water (Siesser and Rogers, 1976), or as a detrital mineral derived from recent evaporitic deposits precipitated on the flood plain of the Tinto river (Fernindez Caliani and Galan, in press), or from phosphogypsum wastes stored on the river banks. Comparison with sediment mineralogy from other coastal systems of south-western Spain, e.g. the mouth of the Guadalquivir river (Mel&-es, 1973) and the bay of Cadiz (Gutierrez Mas et al., 1996), reveals the generalized lack of smectites in sediments of the study area. It is fairly consistent with the mineralogical composition of the sediments delivered by the Tinto and Odiel rivers into

196

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U

198 (1997)

181-200

US

Factor 1 Fig. 8. Plot of principal component analysis showing variable loadings of the first two factors. Textural abbreviations are given in Table 1. Table 6 Metal pollution assessment of predetermined clusters, based on the geoaccumulation index Group

Cluster Cluster Cluster Cluster

Metal

1 2 3 4 A B

Cr

CU

Pb

As

Zn

Hg

Cd

Ni

MP UP-UMP UP UP UP

SP MSP UP UP UMP-MP

SP MP-MSP UP-UMP UP UP-UMP

SP MSP UP UP UP-UMP

MSP-SP UMP-MSP UP UP UP-UMP

SP MSP-SP UP UP UMP-MP

MSP UMP-MP UP UP UP

UMP-MP UP UP UP UP

Igeo-class < 1, unpolluted (UP); 1-2, unpolluted to moderately polluted (UMP); 2-3, moderately polluted (MP);3-4, moderately to strongly polluted (MSP); > 4. strongly polluted (SP).

the estuary since their acidic waters are devoid of smectite suspensions, due to chemical dissolution induced by acid mine drainage (FernAndez Caliani et al., 1996; Gal& et al., 1996). On the other hand, the relative frequency of the mineral phases in sediments is closely related to the grain-size distribution. Quartz, feldspars and shell fragments of calcite or aragonite are usually concentrated in sand-size fractions,

whereas phyllosilicates occur typically in the finer fractions. Textural parameters of the sediments reflect the influence of prevailing hydrodynamic processes. Littoral drift currents promote the transport of siliciclastic sand-size sediments from the Portuguese coast to the Spanish near-shore zone (Cuena, 1990, which explain the occurrence of moderate to well-sorted sands on the continental shelf. By contrast, poor to very poor sorted

.I. C. Fedndez

\\I

Caliani

et al. / The Science of the Total Environment

Odiel River

197

I98 (I 997) I81 -200

#Y Cluster 1 Cluster 2

Tinto River

Padre Santo Channel

ATLANTIC OCEAN

I

Cluster 3

‘-

Cluster 4 -

5Km

\

Fig. 9. Lacation map of clusters determined on the basis of textural, mineralogical and geochemical variables.

sediments found in both sides of the bank are characterized by the scarcity of clays because of the remobilization of fine-grained particles by tidal currents and wave activity, taking place to formation of coarse lag deposits on the inner side and extensive sandy beaches on the outer side, respectively. Clay-size particles increasing in sediments at the seaward end of the Padre Santo channel can be explained by flocculation and differential settling of clay minerals as a result of fluvial and marine water mixing. Relating to heavy metal content of the estuarine sediments, our data are consistent with previous studies (e.g. P6rez et al., 1991; Nelson and Lamothe, 1993) suggesting extensive pollution by toxic metals derived from natural erosion of the

outcropping sulphide deposits and mining activities that have occurred in river catchments since prehistoric times. The high concentrations of sulphide-associated metals such as copper, lead, zinc, cadmium and arsenic must be emphasized because of their strong impact on the environment (Salomons, 1995). At the same time, in the estuary sediments other non-sulphide metals occur, such as chromium, nickel and mercury, indicating an additional anthropogenic source for heavy metal contamination, which is closely associated with industrial discharges (Nelson and Lamothe, 1993). Heavy metal distribution in the estuary and adjacent continental shelf shows a dispersal pattern with well-defined areas of different contami-

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et

al.

/ The Science of the Total Environment

nation ranges. By far, the most polluted area is located at the confluence of the Tinto and Odiel rivers, which constitute the main pathways by which metallic pollutants reach the estuary as shown by Fernindez Caliani et al. (1996). Heavy metals carried by the Tinto river display a great affinity for clay fraction as this fraction is enriched in phyllosilicates respective to the whole sediment. Estuarine mixing leads to a depositional acceleration of clay minerals due to salinity change, favouring the entrapment and accumulation of metal adsorbed on clay particles (Konta, 1991). However, taking into account that kaolinite and illite have only small specific surfaces and their cation exchange capacities are relatively low (Newman, 1987), it is reasonable to assume that a proportion of most metals are adsorbed or are precipitated as coating onto amorphous or poorly crystallized components of the sediments (Gal& et al., 1996). In this way, the ox&hydroxides of iron provide suitable metal holding substratum as they are abundant and have high specific areas (Johnson, 1986). Likewise, from a five-step sequential extraction procedure, Ptrez et al. (1991) have demonstrated that important proportions of the toxic metals are bonded in the easily soluble and reducible chemical fractions, where they represent a hazard for the environment. In any case, it can be concluded that the Huelva estuary acts as a storage basin for pollutants. The concentrations of all the metals decreases greatly towards the estuary mouth, as well as slightly above background levels in the marine sediments. This is interpreted as a consequence of dilution by less metal-enriched coarse sediment. Much lower concentrations of most heavy metals in sediments along Padre Santo channel are due to grain-size effect. Moreover, the sediments of this dredged channel have not had sufficient time to accumulate a high metal content, by which they show very low geoaccumulation indices. Since the element loaded plume from the estuary flows parallel to the coast in a south-eastern direction, in accord with prevailing littoral drift current, the sediments from Mazagcin are moderately polluted. In contrast, the sediments from Punta Umbria sector receive little or no significant metal inputs from rivers, and because

198 (1997)

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of this their heavy metal concentrations are close to background values. At the present time, the fate of the polluting elements which are discharged into the marine environment is not well known. Elbaz-Poulichet and Leblanc (1996) have recently suggested that the trace metal enrichments detected by Van Geen et al. (1991) in the south-west Spanish Atlantic waters can be explained by the high metal fluxes through the Tinto and Odiel rivers to the ocean. Thus, the Huelva estuary is an important potential source of contamination on a regional scale, and so the mechanisms whereby the metallic pollutants are introduced into the Atlantic ocean must be a subject of future research. In conclusion, mineral and heavy metal distributions in sediments of the lower estuary of Huelva and adjoining continental shelf reflect the interrelationships between fluvial and marine processes in an environmental framework strongly stressed by anthropogenic impacts. References AMA (1993) (Agencia de Medio Ambiente). Plan de policia de aguas de1 litoral andaluz. Junta de Andalucia, unpublished report, 132 pp. AMA (1989) (Agencia de Medio Ambiente). Medio Ambiente en Andalucia. Junta de Anadalucia, 356 pp. Amigtr, J.M., Bastida, J. Sanz, A. and Serrano, J. (1994) Crystallinity of lower cretaceous kaolinites of Teruel. App. Clay Sci. 9, 51-69. Anderberg, M.R. (1973) Cluster analysis for applications. Academic Press, New York, 359 pp. Borrego, J. (1992) Sedimentologia de1 Estuario de1 Rio Odiel (Huelva, SO Espasa). Ph. Thesis, Univ. Sevilla (unpublished), 311 pp. Borrego, J., Morales, J.A. and Pendbn, J.G. (1993) Holocene filling of an estuarine lagoon along the mesotidal coast of Huelva: the Piedras River mouth, southwestern Spain. J. Coastal Res. 9, 242-254. Borrego, J., Morales, J.A. and Pendbn, J.G. (1995) Holocene estuarine facies along the mesotidal coast of Huelva, south-western Spain, In: W.A. Flemming and A. Batholom& (Eds.), Tidal signatures in modern and ancient sediments. Int. Ass. Sediment. Spec. Publ. 24, pp. 151-170. Cabrera, F., Conde, B. and Flores, V. (1992) Heavy metals in the surface sediments of the tidal river Tinto (SW Spain). Fres. Environ. Bull. 1, 400-405. Cuena, G.J. (1991) Proyecto de regeneracibn de las playas de Isla Cristina. Memorias Ministerio de Obras Pfiblicas y Transportes, 48 pp.

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Dabrio Cl. and Polo, M.D. (19871 Holocene sea-level changes, coastal dynamics and human impacts in southern Iberian Peninsula, In: C. Zazo (Ed.), Late Quaternary Sea-level Changes in Spain, pp. 227-247. Edzwald J.K. and O’Melia. CR. (1975) Clay distribution in recent estuarine sediments. Clays Clay Min. 23, 39-44. Elbaz-Poulichet, F. and Leblanc, M. (1996) Transfer de metaux dune province mini&e Q l’ocean par des fleuves acides (Rio Tinto, Espagne), CR. Acad. Sci. Paris, 322, 1047-1052. Femandez Caliani, J.C. and Galan, E. (1991) Las pizarras de la Faja Piritica Iberica (Zona Sur-Portuguesa): Geologia, mineralogia y aplicaciones industriales, Estudios Geol. 47, 295-303. Femandez Caliani, J.C. and Gal&r, E. in press. Formation de yeso autigenico en la 1Ianura de inundation de1 rio Tinto (Huelva). Geogaceta. Femindez Caliani. J.C., Requena A. and Galan, E. (19961 Clay mineralogy and heavy metal content of suspended sediments in an extremely polluted lluvial environment: the Tinto river (SW Spain). Preliminary report, In: M. OrtegaHuertas, A. Mpez-Galindo and I. Palomo (Eds.), Advances in Clay Minerals, 218220. Feuillet J.P. and Fleischer, P. (1980) Estuarine circulation: controlling factor of clay mineral distribution in James river estuary, Virginia. J. Sedim. Petrol. 50, 267-279. Flor, G. (1990) Tipologia de dunas e6licas. Procesos de erosion-sedimentation costera y evolution litoral de la provincia de Huelva (Golf0 de Cadiz Occidental, Sur de Espana). Estudios Geol. 46, 99-109. Forstner, U. (1983) Metal pollution in the aquatic environment. Springer-Verlag, Berlin. 472 pp. Galin. E., Fernindez Cafiani, J.C. and Requena, A. (19961 Provenance and evolution of clay minerals in the Tinto river, SW Spain, Proc. 14th Conf. Clay Min. Petrol. BanskP Stiavnica, Slovakia. Gonzalez-Regalado, M.L., Ruiz Muiioz, F. and Borrego, J. (1996) Evolution de la distribucidn de 10s foraminiferos bentonicos en un medio contaminado: El estuario de1 rio Odiel (Huelva, SO Espafia). Rev. Esp. Paleont. 11, l-10. Gutierrez Mas, J.M., Achab, M., Sanchez Bell&, A., Moral Cardona. J.P. and Aguayo, F.L. (1996) Clay minerals in recent sediments of the Cddiz bay and their relationships with the adjacent lands and the contiental shelf, In: M. Ortega-Huertas, A. Lopez-Galindo and 1. Palomo (Eds.), Advances in Clay Minerals. 121-123. IE (19921 (Instituto Espanol de Oceanogra&a), Variation espatio-temporal de par&metros l&o-quimicos y biologicos en la ria de Huelva y area de influencia, en el period0 1987-1991. Internal report no. 138,103 pp. IGME (1974) (Instituto Geol-gico Miner0 de Espaiia). Investigaci6n minera submarina en el subsector ‘Huelva I’, Golfo de Cadiz. Serv. Publ. Ministerio Industria, 134 pp. Johnson, C.A. (19861 The regulation of trace element concentrations in river and estuarine waters contaminated with acid mine drainage: The adsorption of Cu and Zn on amorphous Fe oxyhydroxides. Geochim. Cosmochim. Acta, 50, 2433-2438.

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Van Geen, A. Boyle, E.A. and Moore, W.S. (1991) Trace metal enrichments in waters of the Gulf of Cad& Spain. Geochem. Cosmochim. Acta, 55,2173-2191. Veniale, F. and Setti, M. (1991) Clay minerals tracers for suspended particulate transport and dispersion in coastal environments. Proc. 7th Conf. Euroclay, Dresden. Weaver, C.E. (1989) Clays, muds and shales. Developments in sedimentology, Elsevier, Amsterdam, 819 pp. ziillmer, V. and Irion, G. (1993) Clay mineral and heavy metal distributions in the north-eastern North Sea. Mar. Geol. 111,223-230.