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Biogeochemical evolution of trace elements in a pristine watershed in the Brazilian southeastern coastal region
Applied Geochemistry 16 (2001) 1139±1151
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Biogeochemical evolution of trace elements in a pristine watershed in the Brazilian southeastern coastal region Francisco C.F. DePaula, Antonio A. Mozeto * Universidade Federal de SaÄo Carlos, Departamento de QuõÂmica, LaboratoÂrio de BiogeoquõÂmica Ambiental, Caixa Postal 676, SaÄo Carlos - SP, CEP 13565-905, Brazil Received 12 December 1999; accepted 1 August 2000 Editorial handling by G. Ferris
Abstract Establishing `reference sites' is a dicult task and a critical factor in determining the baseline functioning of ecosystems. The information thus obtained on nutrient and contaminant background concentrations in turn subsidizes the remediation of impacted landscapes. This paper reports a study on metal (Cr, Cu, Pb, Zn, Mn, Fe and Al) and nutrient (C) distribution in sediments from Capivari River watershed (Praia do Sul Biological Reserve, Ilha Grande, Rio de Janeiro State, Brazil), an area where typical SE Brazilian coastal ecosystems are located. Contrary to what one would expect from the high rate at which these ecosystems have been deteriorating in recent decades, the study site is surprisingly well preserved. The present study was developed to assess variations in heavy metal concentrations in river basin sediments, to identify the geochemical carriers of these elements, and determine the in¯uence of water quality and organic matter on their distribution. Results showed that heavy metal distribution has been in¯uenced by the natural biogeochemical properties of those ecosystems found in an upland-to-lowland sequence in the watershed. Minimum and maximum total concentration were: 5 and 23 mg/kg for Cr; 4 and 29 mg/kg for Cu; 13 and 53 mg/kg for Pb; 24 and 142 mg/kg for Zn; 54 and 342 mg/kg for Mn; 0.8 and 7.2% for Fe; 0.5 and 4.9% for Al; 6.3 and 25% for C. The pH and EH are the key-parameters in explaining total metal concentration decrease in the swamp area, where dissolution processes and losses through metal transport seem important. The most important geochemical carriers are Al in the basin's ``continental'' stretch and Fe in the estuarine portion. The data also provide evidence showing that organic matter is the key-parameter in Cu concentration control in the sediments through burial and accumulation processes especially in the swamp area. Heavy metal concentrations in sediments from the study area are generally lower than those found in similar regional ecosystems. Surface enrichment in heavy metal concentrations in collected sediment cores was not observed. The authors therefore conclude that this site is suitable as a `reference site' for studies on the biogeochemistry and ecotoxicology of SE Brazilian coastal ecosystems. # 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction The coastal zone is an ecotone between continental and marine environments and receives energy and materials from both. Such advantages combined with sheltered conditions have strongly attracted human
* Corresponding author. Fax: +55-16-260-8350. E-mail address: [email protected] (A.A. Mozeto).
populations throughout history. In recent years, these areas have suered substantial alterations stemming from xenobiotic (organic) substances and heavy metal discharges due to industrial activities; harbor construction and maintenance; and demographic growth. Most of Brazil's industrial activities and urban development is concentrated along the Southeastern coast. Thus major alterations in ecosystem structure and functioning are quite common and have been reported elsewhere. Fortunately, the Praia do Sul Biological Reserve contains
0883-2927/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(00)00084-6
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most of the ecosystems found along the SE coast. Because these ecosystems are still largely unspoiled they oer an unique opportunity for studying natural or background functioning. Such studies are crucial in making informed decisions aimed at mitigating regional environmental problems. In this paper the authors present a study focusing on the biogeochemistry of heavy metals found in the ecosystems sediments of a small watershed, the Capivari River basin, Ilha Grande, Rio de Janeiro, SE Brazil.
2. Study area The ``Praia do Sul Biological Reserve'' (PSBR) is located on an island (Ilha Grande; 23 S; 44 W), South of Rio de Janeiro State, on the Brazilian Southeastern coast (Fig. 1), the country's most developed and most degraded coastal stretch. Within 3600 ha the PSBR contains most of the ecosystems of the biome ``Mata AtlaÆntica'' (Atlantic Rain Forest), e.g. rain forest, freshwater swamp, lagoons, mangroves, ``restinga''
Fig. 1. Study area map and sampling location points.
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(beach ridges), beaches and rocky shore. The climate is tropical, hot and wet, with annual precipitation up to 2.0 m, and lacking a well-de®ned dry season. Average minimum and maximum temperatures range from 20 to 27 C. Regional geomorphology is typi®ed by the Serra do Mar Ridge reaching 1031 m ASL on Ilha Grande. The bedrock is pre-Cambrian, with high to medium metamorphic grade rocks (migmatites, gneisses and, predominantly on the Reserve, charnockites), and basic intrusives represented by diabase, basalt and gabbro dikes. Sedimentary unconsolidated formations deposited during the last sea regression (late Pleistocene and Holocene) form a 5 km2 coastal plain. There are 3 vegetation groups within the area: (1) rain forest (80% of the Reserve) on the crystalline and colluvial fan terrain; (2) ``restinga'' vegetation (most of the coastal plain area); and (3) mangrove (fringing the lagoon and the channel to the sea) (ArauÂjo and Oliveira, 1988). The Capivari River is the most important in the PSBR. In the uplands, the river with extremely clear water is surrounded by forests on crystalline substrate. The terrain is very steep in this region of large boulder transport. In its middle reach, river transport capacity diminishes, and the boulders become rare, small and rounded. Where it meets the coastal plain, the slope is drastically reduced, spreading the water over a large area, thus forming a swampy environment with trees, shrubs, and sand±clay sediments. The river then ¯ows into a shallow lagoon containing black organic sediments. The waters then become brackish, remaining so until the end of the channel connecting the lagoon to the sea, with sandy sediments characteristic of quartz-bearing substrate, the ``restinga'' ecosystem. The Capivari River watershed was chosen for this study because of its diverse ecosystems, limited size (800 ha), and pristine characteristics. Along its margins there are no signs of human activities, other than the ruins of sugar-cane farms dating from the 18th and 19th centuries. 3. Methodology The study area is composed of various ecosystems, namely: riverine, swamp, lagoon, mangrove and the channel to the sea. Bottom sediment samples were collected manually with a plastic shovel at 14 dierent stations distributed along the studied watershed (Fig. 1) and stored in plastic bags. Water depth varied from a few centimeters at the headwaters to 1 m or more in the channel. Sampling sites were: 1±6 (headwater environment), 7 (swamp area), 8A, B and C (lagoon), 9A, B and C (mangrove on the lagoon shore) and 10±14 (along the channel). The ®rst sampling station in the channel is located downstream from the lagoon mouth and the last one 1.5 km away, at the channel's end, close to the
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ocean. Sediment samples were sieved in the laboratory for grain size analysis. Metal and C analysis was performed in the fraction with grain size less than 63 mm. Two short sediment cores, one from the swamp (23 cm long) and the other from the central portion of the lagoon (25 cm long), were manually retrieved using a gravity collector (Ambuhl and Buhrer, 1975). The water depth was approximately 0.5 m in the swamp and 1.0 m in the lagoon. In the ®eld both cores were sliced every 1 cm and stored in plastic bags, the ®ne fraction (<63 mm), was sieved in the laboratory, for chemical analysis. Four sampling stations were selected for determination of total suspended solids (TSS) (Fig. 1). Two were located in the headwater portion of the watershed (MP 01 and 02), one between the swamp and the lagoon (MP 03), and the last one (MP 04) near the channel mouth. Pre-calcined, weighed (GFC) and pre-dried, weighed cellulose acetate ®lters (0.45 mm pore size) were utilized for ®eld ®ltration. Water quality parameters for waters overlaying the sediments were measured in the ®eld using speci®c electrodes in portable meters. Salinity was measured with an ATAGOTM S-10 hand refractometer and EH and pH using a FEMTOTM 420, respectively with Pt±AgCl and glass electrodes. Electric conductivity was measured using an ANALIONTM C-702. Dissolved O2 was measured using a YELLOW-SPRINGTM 58 m. Metal (Al, Fe, Mn, Cr, Cu, Pb and Zn) total concentrations were determined after acid digestion of 0.5 g dry sediment, using 10 ml concentrated HF and 10 ml concentrated HNO3, in Te¯on bombs at 100 C. The potentially bioavailable fraction of metals (Cr, Cu, Pb and Zn) in the sediment is operationally de®ned as the fraction extracted by weak acid attack (1.0 g sediment shaken in 25.0 ml 0.1 N HCl during 2 h, at room temperature) accordingly to Fiszman et al. (1984). Extracts were analyzed using conventional atomic absorption spectrophotometry. Total C concentrations in sediments, particulate trapped in ®lters, and elutriate (dissolved) were determined using a Shimadzu TOC Analyzer coupled with a Solid Sample Module (SSM-5000A). Based on duplicate sediment samples analytical precision for total metal concentration and the bioavailable fraction was less than 5% for all metals. Relative error for C analyses was 0.3%. Accuracy could only be estimated relative to total metal concentration by analyzing a standard sediment (estuarine sediment; 1646a) from the National Institute of Standards & Technology (NIST, 1995). The recovery percentage from the NIST standard was: 91, 95, 96, 90, 105, 108 and 97%, for Al, Fe, Mn, Cr, Cu, Pb and Zn, respectively. A multivariated statistical analysis (discriminant analysis) was performed, using SGPLUSTM software, in order to assess the geochemical carriers acting in the studied basin.
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4. Results and discussion 4.1. Grain size Sediment grain size from the Capivari River watershed can be classi®ed according to the well-known Shepard classi®cation (Suguio, 1973) as sandy (>75% of sand). The only exception is the swamp, classi®ed as sand±clay (64% sand, 16% silt and 20% clay) (Fig. 2). Despite this apparent uniformity, various factors control grain size distribution. The medium sand fraction predominates in headwaters because of the steep topography. The reduced slope at the swamp with its notable pelitic fraction of bulk sediment, is a sedimentary environment, also characteristic of lagoon and mangrove. The sand fractions in the water channel again predominates, but the ®ne sand fraction becomes more signi®cant due to grain size selection caused by the sea, a process suggested by Amador (1985) to have occurred during the ``restinga'' build-up. 4.2. Hydrochemistry Electrical conductivity, which the study shows as having an increase corresponding to 3 orders of magnitude along the entire basin, characterizes most clearly surface water hydrochemistry (Fig. 3). Values range from 50 mS/cm at the ®rst sampling point up to 22 600 mS/cm at the one nearest to the sea. The pH values are slightly acidic (5.5±6.9) in the ``continental'' portion of the basin; in the estuarine portion, values range from acidic (4.9) to basic (7.9). Tidal pulse in¯uence extends into the lagoon, thus determining salinity variation (2.5± 4.0%), electrical conductivity (3000±4000 mS/cm), and pH (6.4±7.1). However, pH can hardly be buered by either the slightly acidic upstream freshwater, or acidic blackish water from the ``restinga'' (DePaula et al., 1998). These results agree with preliminary data surveyed in both the studied area (DePaula et al., 1998)
and the PerequeÆ River at Ilha do Cardoso. This site is also a Reserve area in the SE Brazilian coastal region, sampled for two years by Moulton (1993). The highest pH value (7.9) was measured at the farthest downstream sampling point aected by marine waters, a pattern not reported by Moulton (1993), who probably did not sample the estuary waters. The present study shows dissolved O2 saturation greater than 100% in the headwater sites due to local falls and rapids. The lowest values were found in the swamp (30±75%), lagoon (60±101%), and mangrove (44±80%) sites (Fig. 3). Waters in these areas are either stagnant or show little renovation, and sediments have high organic content, both factors probably contributing to O2 depletion in the waters. Accordingly, the lowest EH value (110 mV) was found in the swamp (even the maximum value for this area, 213 mV, is the smallest of all the maximum values for the studied basin) (Fig. 3). 4.3. Organic matter Total C concentration in sediments clearly increases from headwaters (6.3%) to estuary (up to 25%) (Fig. 4A). Corresponding to known high primary productivity rates in estuarine areas (Odum, 1977), and favorable C accumulation conditions. Dissolution of organic matter in the lagoon via oxidation processes is likely to be responsible for increased dissolved organic C concentrations (Fig. 4B). As a result, local waters are darker. 4.4. Total metal concentration Comparison of total heavy metal concentrations found in sediments at Capivari River watershed, with those of similar regional ecosystems (identical climate, topography, and geology) show dierent degrees of anthropogenic disturbances, showing that values from the studied area are smaller or at most least comparable. The observations presented below demonstrate that:
Fig. 2. Grain size distribution in selected sediment samples from Capivari River watershed (SE Brazil). Sampling point number in brackets.
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Chromium concentrations in the riverine environment (see Fig. 5) ranged from 7 to 19 mg/kg; Cr concentrations in sediments from an agricultural region of Rio de Janeiro State (Marica Lagoon watershed Ð Barroso et al., 1991), from 28 to 90 mg/kg; sediments from the Acarõ River (Rego et al., 1993) (located in the urbanized and industrialized Rio de Janeiro metropolitan area) from 53 to 100 mg/kg; Cr content in lagoon sediments from PSBR, ranged from 17 to 22 mg/kg, by far the lowest of all regional lagoons. For instance, values as high as 49 mg/kg and from 50 to 98 mg/kg were respectively reported by Patchineelam et al. (1988) for the Guarapina Lagoon and Fernandes et al. (1993) for the Jacarepagua Lagoon sediments. Copper concentrations in sediments from the riverine environment were between 10 and 26 mg/kg, similar to the 30 mg/kg cited for the Frade River (non-impacted stream near the Reserve) by Lacerda et al. (1987). However, this value is lower than that measured in the Acarõ River sediments (500±2700 mg/kg) (Rego et al., 1993). The same trend was found when comparing lagoon Cu concentrations, where values from the PSBR
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(12±16 mg/kg) are smaller than those from Guarapina Lagoon (30 mg/kg) (Patchineelam et al., 1988) and Jacarepagua Lagoon (24±105 mg/kg) (Fernandes et al., 1993). Copper concentrations in the mangrove sediment at the study site (13±18 mg/kg) (Lacerda et al., 1989) fall within the range of non-impacted mangroves on the Brazilian SE coast (3±42 mg/kg), but they are smaller than those for impacted ones in the same region (ranging from 12 to 130 mg/kg) (Lacerda et al., 1989). Lead data from Capivari River sediments (36±53 mg/ kg) bracket those in the Frade River sediments (45 mg/ kg) (Lacerda et al., 1987), but are smaller than those reported for Acarõ River sediments (110±440 mg/kg) (Rego et al., 1993). Lead concentration in lagoon sediments (46±62 mg/kg) is similar than those from the Jacarepagua Lagoon (26±60 mg/kg) (Fernandes et al., 1993) and half of that in the Guarapina Lagoon (120 mg/kg) (Patchineelam et al., 1988). Zinc concentration in the sediments attest to the pristine character of the Capivari River watershed: values range from 100 to 142 mg/kg in the riverine environment sampling points, resembling those of the
Fig. 3. Average (O), maximum, and minimum values for hydrochemistry parameters in surface waters in Capivari River watershed (SE Brazil).
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Frade River (110 mg/kg) (Lacerda et al., 1987) and Marica Lagoon watershed sediments (96±140 mg/kg) (Barroso et al., 1991), and considerably smaller than the Zn content in the polluted Acarõ River sediments (700± 1400 mg/kg). In the lagoon Zn concentrations fall to between 60 and 87 mg/kg, while Guarapina Lagoon sediments show Zn concentrations of 110 mg/kg (Patchineelam et al., 1988) and Jacarepagua Lagoon, from 200 to 255 mg/kg (Fernandes et al., 1993). Manganese in sediments shows widely ranging values, even when compared to less impacted areas. As an example, concentrations of 96 to 196 mg/kg Mn were found in the Capivari River (this study) and 260 mg/kg in the Frade River (Lacerda et al., 1987). Again comparing the present data to that from impacted areas, lagoon values range from 279 mg/kg in the Capivari River watershed to 370 mg/kg in Jacarepagua Lagoon (Fernandes et al., 1993) and 100 mg/kg in Guarapina
Lagoon (Patchineelam et al., 1988), results probably related to the high Mn geochemical mobility in supergene environment (Rose et al., 1979). Iron shows similar concentrations for river sediments: 4.3±6.4% in the Capivari River (this study), 4.2% at Frade River (Lacerda et al., 1987), and 3.3±4.7% at Acarõ River (Rego et al., 1993). Lagoon sediment for this study have a 6.3±7.2% total Fe concentration, with 5.8% at Guarapina Lagoon (Patchineelam et al., 1988) and 6.5% at Jacarepagua Lagoon (Fernandes et al., 1993). Mangrove sediments show the largest range of values, varying from 2.5 to 5.8% Fe at the Capivari River watershed (this study) and 0.7±6.2 for mangroves in the SE Brazilian coastal region (Lacerda et al., 1989). Aluminum was not analyzed in most of the studies referred to here and is rarely mentioned in the literature. Aluminium concentrations in the lagoons therefore can only be compared with one another, and results showed
Fig. 4. Carbon at Capivari River watershed (SE Brazil). 5% error bars. (A) Total C concentration in sediments. Points 1±6=river; 7=swamp; 8A, B and C=lagoon; 9A, B and C=mangrove; 10±14=channel. (B) Carbon speciation. Points MP 01 and 02=¯uvial; MP 03=lagoon; MP 04=water channel.
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that sediments found in the Capivari River watershed (this study) ranged from 2.8 to 4.9%, far below the 8% found in Guarapina Lagoon (Patchineelam et al., 1988) and the 10% in Jacarepagua Lagoon (Fernandes et al., 1993). For these reasons, the PSBR quali®es as a `reference site' for heavy metals in sediments along the Brazilian SE coast. The heavy metal data (total concentration) from sediments determined in the chain environments (Fig. 5) show a clear horizontal evolution in response to natural inputs/outputs and biogeochemical processes.
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A general trend is apparent for all metals in the swamp site (sampling point ] 7), where a decrease in total concentrations with respect to the upstream riverine environment occurs. This decrease is partially caused by an increase in organic matter content (see Fig. 4A), which results in diluted total concentration. The authors also postulate that physico±chemical characteristics of the water in this area (i.e. low pH, EH and DO) (see Fig. 3) enhance this trend, as corroborated by Fig. 6, the stability diagram of Fe forms (modi®ed from Brookins, 1988), which includes pH and EH values from the studied basin. All sampled environments except the swamp
Fig. 5. Total metal concentration in sediments of Capivari River watershed (SE Brazil). 5% error bars.
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and the lagoon, show values covering both ®elds of metal partitioning (i.e. particulate and dissolved forms). The swamp values are restricted to that favoring the dissolved form, while those of the lagoon are restricted to the particulate ®eld. This phenomenon is also thought to be responsible for the decrease in the swamp in total metal concentration mostly of Fe, and to a lesser degree of Zn and Cu. At the lagoon (sampling points ] 8A, B and C) all metals showed a total concentration increase (Fig. 5) typical for coastal lagoons (Hart, 1982; Lacerda, 1994). Although likely to result from inherent area sedimentary characteristics, this tendency may also be a function of
reprecipitation of elements dissolved in the upstream swamp. Data from the mangrove sites plot roughly between headwater and lagoon environments, thus showing behavior representing fringe sites between terrestrial and water bodies. Total heavy metal concentrations in the channel sediments decrease from upstream to downstream sampling points, i.e. from point 10 to 14 (Fig. 5). Copper is an exception at point ]10, probably associated with local high organic content, the highest for the entire basin. From this sampling point on towards the sea, Fe, Al and Mn concentrations show a progressive decrease, promoted by dilution with incoming marine sediments,
Fig. 6. Stability ®eld diagram for Fe, adapted from Brookins (1988) including pH and EH values from environments in Capivari River watershed (SE Brazil).
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Fig. 7. Percentage of total metal concentration present as potentially bioavailable fraction, in the sediments of Capivari River watershed (SE Brazil). Points 1±6=¯uvial; 7=swamp; 8A, B and C=lagoon; 9A, B and C=mangrove; 10±14=channel.
usually low in such elements. In the middle part of the channel sediments show Pb and Zn increases, probably attributed to the so-called `maximum turbidity phenomena' (Salomons and FoÈrstner, 1984). Only Cr and Cu concentrations do not completely follow the pattern shown for the other metals; instead, an erratic Cr distribution along the channel was observed (although representing a dilution curve if sampling point ]12 is ignored). For Cu two extremely high concentration values were determined for sampling stations 10 and 14. The ®rst may be associated with high organic matter content, with the second resulting from an adjacent small elevation were the concentration is equivalent to those in the headwaters.
values than those from upstream environments. Mangrove sediments show a slight increase in concentration when compared to those from the lagoon (except for Zn). However, the pattern remains the same, i.e. Cr
4.5. Potentially bioavailable metal concentration Concentration (expressed as % of total metal concentration) of the potentially bioavailable fraction of Cr, Cu, Pb and Zn in the sediments increases from inland to the estuarine portion of the basin (Fig. 7). This is likely and the direct result of the intense estuarine zone dynamic, where tides change twice a day and ¯uvial and marine conditions, waves and currents promote resuspension of bottom materials. These characteristics aect reversible processes such as sorption/desorption, favoring the bioavailability of heavy metals and their release from particles into the water. Consequently, lagoon sediments at the estuarine zone show, for every element except Pb, larger concentration
Fig. 8. Discriminant analysis. DF=discriminant function. R=river stations; S=swamp; L=lagoon stations; M=mangrove stations; C=channel stations.
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4.6. Geochemical carriers In the present study 3 heavy metal geochemical carriers were considered: (1) mineral lattice, represented by Al; (2) Fe and Mn oxy-hydroxides; and (3) organic matter, represented by C. Carbonate, a fourth possible geochemical carrier, was discarded because of its virtual absence in Capivari River watershed sediments. Once established the 5 environmental groups, by using the data on both the total and potentially bioavailable fraction of metal and total carbon concentration from sediments representing them, a discriminant analysis identifying the variables characterizing each environment was performed (Legendre and Legendre, 1983).
Two discriminant functions were responsible for 95% of the data variation. The ®rst one (73%), like the second (22%), relate to total Fe and Al. Both functions are graphically represented in Fig. 8 for samples from river (``R''), swamp (``S''), lagoon (``L''), mangrove (``M'') and channel (``C'') environments. The left-hand side of the plot represents Al. In the river and the swamp areas the mineral lattice is the most important heavy metal carrier. The right-hand side of the diagram plots data from environments where Fe oxy-hydroxides are the most important metal transport form. These results corroborate the postulated horizontal heavy metal evolution for the studied basin. They make obvious the importance of estuarine dynamics, where upstreamordered minerals are altered and amorphous or poorly
Fig. 9. Total metal and C concentration in the sediment core extracted from the swamp site at Capivari River watershed (SE Brazil). Fe, Al and C in%. The others in mg/kg.
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crystallized forms start to predominate. However, even at the estuary a possible distinction exists among environments, represented by the second discriminant function (DF 2). The lagoon sampling points at the top of the plot relate to Al while at the bottom mangrove and channel sampling points plot close together in the Fe ®eld. Based on these results it is postulated that the lagoon is a true ecotone between land and sea where both altered and ordered mineral forms coexist. 4.7. Sediment cores Two short cores were taken from sedimentary areas of Capivari River watershed: one at the swamp (Fig. 9) and other at the lagoon (Fig. 10). Concentration pro®les
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for various metals show no enrichment or depletion trend with depth, except for C and, to some extent, Cu (Fig. 9), an expected result since no anthropogenic source metal is found in the area. At the swamp (Fig. 9), oscillations in concentration pro®les up to 10 cm in depth are likely attributable to the presence of tree and shrub rhizospheres. Root respiration promotes modi®cations in the redox state, and thus changes in metal speciation. A calculated partial correlation using these results shows that Cu signi®cantly correlates with C (a=0.01), the only case where such an association seems to occur. During a reconnaissance survey done at the PSBR by DePaula et al. (1994), lignin-derived phenol contents showed that site organic matter is composed of less degraded, and
Fig. 10. Total metal and C concentration in the sediment core extracted from the lagoon site at Capivari River watershed (SE Brazil). Fe, Al and C in%. The others in mg/kg.
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consequently more reactive, vascular material. Such a characteristic, coupled with the Cu dissolution process mentioned above, seems responsible for the observed correlation. Concentration pro®les for the lagoon are quite constant (Fig. 10); due to the absence of vegetation, no oscillations in concentrations occurred at the top of the core, a pattern again qualifying the study area as a likely `reference site'. The atmospheric Zn transport in the region, determined by Pedlowisk et al. (1991) and Silva Filho (1997) is not signi®cant when compared to the geological load described here. Coastal lagoons are good collectors for atmospheric deposition and in this study no increase in metal concentration in core top was observed. Besides, using Al concentration to normalize the Zn, the ratio shows no trend with depth, presenting a mean value of 19 and standard deviation of 2. The calculated partial correlation based on the results of analysis of the core, showed Al acting as a Zn geochemical carrier, and Fe acting as a Pb carrier during the burial of sediments in the lagoon (a=0.01). As stated above these observations reinforce the previous results characterizing the lagoon as a boundary of this system where both `continental' and estuarine processes can occur simultaneously. 5. Conclusions In spite of the intense rate of degradation in the majority of ecosystems found along the SE coast, the Capivari River watershed is surprisingly well preserved. Heavy metal concentrations in sediments from the successive ecosystems are in general lower than in those found in similar regional ecosystems. Surface heavy metal enrichments in collected sediment cores were not observed. It is therefore concluded that this site quali®es as a `reference site' for studies on the biogeochemistry and ecotoxicology of sediments from similar ecosystems along the SE Brazilian coast, principally the ``Serra do Mar'' region, stretching from Guanabara Bay in Rio de Janeiro south to the Paranagua Bay, in Parana State (Southern Brazilian coast). This portion of the country harbors most industry, shipping, and urban development. The authors believe this work will contribute to increased public awareness concerning feasible recuperation of impacted areas, through programs based on sound scienti®c knowledge. Acknowledgements The authors would like to acknowledge the help of the PSBR personnel in providing ®eld facilities. DePaula received a CAPES scholarship and A. A. Mozeto received a FAPESP research grant (No. 96/
0634-2). We also acknowledge Prof. Paula Ann Matvienko Sikar for the English revision of the manuscript, as well as the two reviewers who provided excellent contributions to the ®rst version of this work. Andre and Rafael Mozeto's (DI Design) design work with the ®gures is also greatly appreciated. References Amador, E.S. 1985. SubsõÂdios geoloÂgicos e geomorfoloÂgicos aÁ elaboracËaÄo do plano diretor da Reserva BioloÂgica Estadual da Praia do Sul. RelatoÂrio Interno. FEEMA, Rio de Janeiro. Ambuhl, H., Buhrer, H., 1975. Zur tecnick der entnahme ungestorer grosse proben von sedimenten; ein verbesserters bohrlot. Schweiz. z. Hydrol. 37, 175±186. ArauÂjo, D.S.D., Oliveira, R.R., 1988. Reserva BioloÂgica Estadual da Praia do Sul (Ilha Grande, Estado do Rio de Janeiro): Lista preliminar da ¯ora. Acta Bot. Bras. 1 (2), 83±94. Barroso, L.V., De Paula, F.C.F., Ovalle, A.R.C., Bidone, E.D. 1991. GeoquõÂmica de sedimentos ¯uviais da Bacia de Marica (RJ) como ferramenta para o gerenciamento de recursos hõÂdricos. SimpoÂsio Brasileiro de Recursos HõÂdricos, IX. Rio de Janeiro, pp. 17±26. Brookins, D.G., 1988. EH-pH Diagrams for Geochemistry. Springer, New York. DePaula, F.C.F., Oliveira, R.R., Carvalho, C.E.V., Ovalle, A.R.C., Barroso, L.V., Rezende, C.E., 1994. Pesquisa geoquõÂmica orientativa na bacia do Rio Capivari, Ilha Grande, RJ. SimpoÂsio de Ecossistemas da Costa Brasileira, 3, Anais. Serra Negra, 382±395. DePaula, F.C.F., Carvalho, C.E.V., Ovalle, A.R.C., Bernardes, M.C., Barroso, L.V., 1998. Water geochemistry in a landscape gradient in an Atlantic Rainforest environment, Ilha Grande, Southeastern Brazil. Verh. Int. Verein. Limnol. 26, 903±906. Fernandes, H.M., Cardoso, K., Godoy, J.M.O., Patchineelam, S.R., 1993. Cultural impact on the geochemistry of sediments in Jacarepagua Lagoon, Rio de Janeiro, Brazil. Environ. Technol. 14, 93±100. Fiszman, M., Lacerda, L.D., Pfeier, W.C., 1984. Comparison of methods used for extraction and geochemical distribution of heavy metals in bottom sediments from Sepetiba Bay, Rio de Janeiro. Environ. Technol. Lett. 58, 567±572. Hart, B.T., 1982. Uptake of trace metals by sediments and suspended particles: a review. Hydrobiologia 91, 299±313. Lacerda, L.D., 1994. Biogeochemistry of heavy metals in coastal lagoons. In: Kjerfve, B. (Ed.). Coastal Lagoons Processes, 8. Elsevier: Amsterdam, pp. 221±241. Lacerda, L.D., Rezende, C.E., Silva, C.A.R., Wasserman, J.C., 1987. Metal composition of sediments from mangroves of SE Braziliam coast. In: Lindenberg, S.E., Hutchinson, T.C. (Ed.). Heavy Metals in the Environments Int. Conf. New Orleans, vol. 2, pp. 464±466. Lacerda, L.D., Souza, C.M.M., Pestana, M.H.D., 1989. Trace metals geochemical associations in sediments of a non-contaminated estuary. CieÆnc Cult. 41, 301±304. Legendre, L., Legendre, P., 1983. Numerical Ecology. Elsevier, New York. Moulton, T.P., 1993. Ecologia dos rios e outros corpos de aÂgua na Ilha do Cardoso, SaÄo Paulo, Brasil. SimpoÂsio de Ecossistemas da Costa Brasileira, 3, Anais. Serra Negra, 172±191.
F.C.F. DePaula, A.A. Mozeto / Applied Geochemistry 16 (2001) 1139±1151 NIST, 1995. Certi®cate of analysis: standard reference material 1646a, estuarine sediment. National Institute of Standards Technology, Gaithersburg. Odum, E.P., 1977. Ecologia, 3rd ed. Pioneira, SaÄo Paulo. Patchineelam, S.R., LeitaÄo Filho, C.M., Kristotakis, K., Tobschall, H.J., 1988. Atmospheric lead deposition into Guarapina Lagoon, Rio de Janeiro State, Brazil. In: Seelinger, U., Lacerda, L.D., Patchineelam, S.R. (Eds.), Metals in Coastal Environments of Latin America. Springer, Berlin. Pedlowisk, M.A., Lacerda, L.D., Ovalle, A.R.C., Wats, P.P., Silva Filho, E.V., 1991. Atmospheric inputs of Zn, Fe and Mn into the Sepetiba Bay, Rio de Janeiro. CieÆnc. Cult. 43 (5), 380±382.
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Rego, V.S., Pfeier, W.C., Barcellos, C.C., Rezende, C.E., Malm, O., Souza, C.M.M., 1993. Heavy metals transport in the AcarõÂ-S.J. de MeritõÂ River System, Brazil. Environ. Technol. 14, 167±174. Rose, A.W., Hawkes, H.E., Webb, J.S., 1979. Geochemistry in Mineral Exploration, 2nd ed. Academic Press, London. Salomons, W., FoÈrstner, U., 1984. Metals in the Hydrocycle. Springer, Berlin. Silva Filho, E.V. 1997. GeoquõÂmica da DeposicËaÄo AtmosfeÂrica no Litoral do Estado do Rio de Janeiro. PhD Thesis. Univ. Federal Fluminense, NiteroÂi. Suguio, K., 1973. IntroducËaÄo aÁ sedimentologia. Editora Edgard Blucher Ltda, SaÄo Paulo.
www.elsevier.com/locate/apgeochem
Biogeochemical evolution of trace elements in a pristine watershed in the Brazilian southeastern coastal region Francisco C.F. DePaula, Antonio A. Mozeto * Universidade Federal de SaÄo Carlos, Departamento de QuõÂmica, LaboratoÂrio de BiogeoquõÂmica Ambiental, Caixa Postal 676, SaÄo Carlos - SP, CEP 13565-905, Brazil Received 12 December 1999; accepted 1 August 2000 Editorial handling by G. Ferris
Abstract Establishing `reference sites' is a dicult task and a critical factor in determining the baseline functioning of ecosystems. The information thus obtained on nutrient and contaminant background concentrations in turn subsidizes the remediation of impacted landscapes. This paper reports a study on metal (Cr, Cu, Pb, Zn, Mn, Fe and Al) and nutrient (C) distribution in sediments from Capivari River watershed (Praia do Sul Biological Reserve, Ilha Grande, Rio de Janeiro State, Brazil), an area where typical SE Brazilian coastal ecosystems are located. Contrary to what one would expect from the high rate at which these ecosystems have been deteriorating in recent decades, the study site is surprisingly well preserved. The present study was developed to assess variations in heavy metal concentrations in river basin sediments, to identify the geochemical carriers of these elements, and determine the in¯uence of water quality and organic matter on their distribution. Results showed that heavy metal distribution has been in¯uenced by the natural biogeochemical properties of those ecosystems found in an upland-to-lowland sequence in the watershed. Minimum and maximum total concentration were: 5 and 23 mg/kg for Cr; 4 and 29 mg/kg for Cu; 13 and 53 mg/kg for Pb; 24 and 142 mg/kg for Zn; 54 and 342 mg/kg for Mn; 0.8 and 7.2% for Fe; 0.5 and 4.9% for Al; 6.3 and 25% for C. The pH and EH are the key-parameters in explaining total metal concentration decrease in the swamp area, where dissolution processes and losses through metal transport seem important. The most important geochemical carriers are Al in the basin's ``continental'' stretch and Fe in the estuarine portion. The data also provide evidence showing that organic matter is the key-parameter in Cu concentration control in the sediments through burial and accumulation processes especially in the swamp area. Heavy metal concentrations in sediments from the study area are generally lower than those found in similar regional ecosystems. Surface enrichment in heavy metal concentrations in collected sediment cores was not observed. The authors therefore conclude that this site is suitable as a `reference site' for studies on the biogeochemistry and ecotoxicology of SE Brazilian coastal ecosystems. # 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction The coastal zone is an ecotone between continental and marine environments and receives energy and materials from both. Such advantages combined with sheltered conditions have strongly attracted human
* Corresponding author. Fax: +55-16-260-8350. E-mail address: [email protected] (A.A. Mozeto).
populations throughout history. In recent years, these areas have suered substantial alterations stemming from xenobiotic (organic) substances and heavy metal discharges due to industrial activities; harbor construction and maintenance; and demographic growth. Most of Brazil's industrial activities and urban development is concentrated along the Southeastern coast. Thus major alterations in ecosystem structure and functioning are quite common and have been reported elsewhere. Fortunately, the Praia do Sul Biological Reserve contains
0883-2927/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(00)00084-6
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most of the ecosystems found along the SE coast. Because these ecosystems are still largely unspoiled they oer an unique opportunity for studying natural or background functioning. Such studies are crucial in making informed decisions aimed at mitigating regional environmental problems. In this paper the authors present a study focusing on the biogeochemistry of heavy metals found in the ecosystems sediments of a small watershed, the Capivari River basin, Ilha Grande, Rio de Janeiro, SE Brazil.
2. Study area The ``Praia do Sul Biological Reserve'' (PSBR) is located on an island (Ilha Grande; 23 S; 44 W), South of Rio de Janeiro State, on the Brazilian Southeastern coast (Fig. 1), the country's most developed and most degraded coastal stretch. Within 3600 ha the PSBR contains most of the ecosystems of the biome ``Mata AtlaÆntica'' (Atlantic Rain Forest), e.g. rain forest, freshwater swamp, lagoons, mangroves, ``restinga''
Fig. 1. Study area map and sampling location points.
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(beach ridges), beaches and rocky shore. The climate is tropical, hot and wet, with annual precipitation up to 2.0 m, and lacking a well-de®ned dry season. Average minimum and maximum temperatures range from 20 to 27 C. Regional geomorphology is typi®ed by the Serra do Mar Ridge reaching 1031 m ASL on Ilha Grande. The bedrock is pre-Cambrian, with high to medium metamorphic grade rocks (migmatites, gneisses and, predominantly on the Reserve, charnockites), and basic intrusives represented by diabase, basalt and gabbro dikes. Sedimentary unconsolidated formations deposited during the last sea regression (late Pleistocene and Holocene) form a 5 km2 coastal plain. There are 3 vegetation groups within the area: (1) rain forest (80% of the Reserve) on the crystalline and colluvial fan terrain; (2) ``restinga'' vegetation (most of the coastal plain area); and (3) mangrove (fringing the lagoon and the channel to the sea) (ArauÂjo and Oliveira, 1988). The Capivari River is the most important in the PSBR. In the uplands, the river with extremely clear water is surrounded by forests on crystalline substrate. The terrain is very steep in this region of large boulder transport. In its middle reach, river transport capacity diminishes, and the boulders become rare, small and rounded. Where it meets the coastal plain, the slope is drastically reduced, spreading the water over a large area, thus forming a swampy environment with trees, shrubs, and sand±clay sediments. The river then ¯ows into a shallow lagoon containing black organic sediments. The waters then become brackish, remaining so until the end of the channel connecting the lagoon to the sea, with sandy sediments characteristic of quartz-bearing substrate, the ``restinga'' ecosystem. The Capivari River watershed was chosen for this study because of its diverse ecosystems, limited size (800 ha), and pristine characteristics. Along its margins there are no signs of human activities, other than the ruins of sugar-cane farms dating from the 18th and 19th centuries. 3. Methodology The study area is composed of various ecosystems, namely: riverine, swamp, lagoon, mangrove and the channel to the sea. Bottom sediment samples were collected manually with a plastic shovel at 14 dierent stations distributed along the studied watershed (Fig. 1) and stored in plastic bags. Water depth varied from a few centimeters at the headwaters to 1 m or more in the channel. Sampling sites were: 1±6 (headwater environment), 7 (swamp area), 8A, B and C (lagoon), 9A, B and C (mangrove on the lagoon shore) and 10±14 (along the channel). The ®rst sampling station in the channel is located downstream from the lagoon mouth and the last one 1.5 km away, at the channel's end, close to the
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ocean. Sediment samples were sieved in the laboratory for grain size analysis. Metal and C analysis was performed in the fraction with grain size less than 63 mm. Two short sediment cores, one from the swamp (23 cm long) and the other from the central portion of the lagoon (25 cm long), were manually retrieved using a gravity collector (Ambuhl and Buhrer, 1975). The water depth was approximately 0.5 m in the swamp and 1.0 m in the lagoon. In the ®eld both cores were sliced every 1 cm and stored in plastic bags, the ®ne fraction (<63 mm), was sieved in the laboratory, for chemical analysis. Four sampling stations were selected for determination of total suspended solids (TSS) (Fig. 1). Two were located in the headwater portion of the watershed (MP 01 and 02), one between the swamp and the lagoon (MP 03), and the last one (MP 04) near the channel mouth. Pre-calcined, weighed (GFC) and pre-dried, weighed cellulose acetate ®lters (0.45 mm pore size) were utilized for ®eld ®ltration. Water quality parameters for waters overlaying the sediments were measured in the ®eld using speci®c electrodes in portable meters. Salinity was measured with an ATAGOTM S-10 hand refractometer and EH and pH using a FEMTOTM 420, respectively with Pt±AgCl and glass electrodes. Electric conductivity was measured using an ANALIONTM C-702. Dissolved O2 was measured using a YELLOW-SPRINGTM 58 m. Metal (Al, Fe, Mn, Cr, Cu, Pb and Zn) total concentrations were determined after acid digestion of 0.5 g dry sediment, using 10 ml concentrated HF and 10 ml concentrated HNO3, in Te¯on bombs at 100 C. The potentially bioavailable fraction of metals (Cr, Cu, Pb and Zn) in the sediment is operationally de®ned as the fraction extracted by weak acid attack (1.0 g sediment shaken in 25.0 ml 0.1 N HCl during 2 h, at room temperature) accordingly to Fiszman et al. (1984). Extracts were analyzed using conventional atomic absorption spectrophotometry. Total C concentrations in sediments, particulate trapped in ®lters, and elutriate (dissolved) were determined using a Shimadzu TOC Analyzer coupled with a Solid Sample Module (SSM-5000A). Based on duplicate sediment samples analytical precision for total metal concentration and the bioavailable fraction was less than 5% for all metals. Relative error for C analyses was 0.3%. Accuracy could only be estimated relative to total metal concentration by analyzing a standard sediment (estuarine sediment; 1646a) from the National Institute of Standards & Technology (NIST, 1995). The recovery percentage from the NIST standard was: 91, 95, 96, 90, 105, 108 and 97%, for Al, Fe, Mn, Cr, Cu, Pb and Zn, respectively. A multivariated statistical analysis (discriminant analysis) was performed, using SGPLUSTM software, in order to assess the geochemical carriers acting in the studied basin.
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4. Results and discussion 4.1. Grain size Sediment grain size from the Capivari River watershed can be classi®ed according to the well-known Shepard classi®cation (Suguio, 1973) as sandy (>75% of sand). The only exception is the swamp, classi®ed as sand±clay (64% sand, 16% silt and 20% clay) (Fig. 2). Despite this apparent uniformity, various factors control grain size distribution. The medium sand fraction predominates in headwaters because of the steep topography. The reduced slope at the swamp with its notable pelitic fraction of bulk sediment, is a sedimentary environment, also characteristic of lagoon and mangrove. The sand fractions in the water channel again predominates, but the ®ne sand fraction becomes more signi®cant due to grain size selection caused by the sea, a process suggested by Amador (1985) to have occurred during the ``restinga'' build-up. 4.2. Hydrochemistry Electrical conductivity, which the study shows as having an increase corresponding to 3 orders of magnitude along the entire basin, characterizes most clearly surface water hydrochemistry (Fig. 3). Values range from 50 mS/cm at the ®rst sampling point up to 22 600 mS/cm at the one nearest to the sea. The pH values are slightly acidic (5.5±6.9) in the ``continental'' portion of the basin; in the estuarine portion, values range from acidic (4.9) to basic (7.9). Tidal pulse in¯uence extends into the lagoon, thus determining salinity variation (2.5± 4.0%), electrical conductivity (3000±4000 mS/cm), and pH (6.4±7.1). However, pH can hardly be buered by either the slightly acidic upstream freshwater, or acidic blackish water from the ``restinga'' (DePaula et al., 1998). These results agree with preliminary data surveyed in both the studied area (DePaula et al., 1998)
and the PerequeÆ River at Ilha do Cardoso. This site is also a Reserve area in the SE Brazilian coastal region, sampled for two years by Moulton (1993). The highest pH value (7.9) was measured at the farthest downstream sampling point aected by marine waters, a pattern not reported by Moulton (1993), who probably did not sample the estuary waters. The present study shows dissolved O2 saturation greater than 100% in the headwater sites due to local falls and rapids. The lowest values were found in the swamp (30±75%), lagoon (60±101%), and mangrove (44±80%) sites (Fig. 3). Waters in these areas are either stagnant or show little renovation, and sediments have high organic content, both factors probably contributing to O2 depletion in the waters. Accordingly, the lowest EH value (110 mV) was found in the swamp (even the maximum value for this area, 213 mV, is the smallest of all the maximum values for the studied basin) (Fig. 3). 4.3. Organic matter Total C concentration in sediments clearly increases from headwaters (6.3%) to estuary (up to 25%) (Fig. 4A). Corresponding to known high primary productivity rates in estuarine areas (Odum, 1977), and favorable C accumulation conditions. Dissolution of organic matter in the lagoon via oxidation processes is likely to be responsible for increased dissolved organic C concentrations (Fig. 4B). As a result, local waters are darker. 4.4. Total metal concentration Comparison of total heavy metal concentrations found in sediments at Capivari River watershed, with those of similar regional ecosystems (identical climate, topography, and geology) show dierent degrees of anthropogenic disturbances, showing that values from the studied area are smaller or at most least comparable. The observations presented below demonstrate that:
Fig. 2. Grain size distribution in selected sediment samples from Capivari River watershed (SE Brazil). Sampling point number in brackets.
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Chromium concentrations in the riverine environment (see Fig. 5) ranged from 7 to 19 mg/kg; Cr concentrations in sediments from an agricultural region of Rio de Janeiro State (Marica Lagoon watershed Ð Barroso et al., 1991), from 28 to 90 mg/kg; sediments from the Acarõ River (Rego et al., 1993) (located in the urbanized and industrialized Rio de Janeiro metropolitan area) from 53 to 100 mg/kg; Cr content in lagoon sediments from PSBR, ranged from 17 to 22 mg/kg, by far the lowest of all regional lagoons. For instance, values as high as 49 mg/kg and from 50 to 98 mg/kg were respectively reported by Patchineelam et al. (1988) for the Guarapina Lagoon and Fernandes et al. (1993) for the Jacarepagua Lagoon sediments. Copper concentrations in sediments from the riverine environment were between 10 and 26 mg/kg, similar to the 30 mg/kg cited for the Frade River (non-impacted stream near the Reserve) by Lacerda et al. (1987). However, this value is lower than that measured in the Acarõ River sediments (500±2700 mg/kg) (Rego et al., 1993). The same trend was found when comparing lagoon Cu concentrations, where values from the PSBR
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(12±16 mg/kg) are smaller than those from Guarapina Lagoon (30 mg/kg) (Patchineelam et al., 1988) and Jacarepagua Lagoon (24±105 mg/kg) (Fernandes et al., 1993). Copper concentrations in the mangrove sediment at the study site (13±18 mg/kg) (Lacerda et al., 1989) fall within the range of non-impacted mangroves on the Brazilian SE coast (3±42 mg/kg), but they are smaller than those for impacted ones in the same region (ranging from 12 to 130 mg/kg) (Lacerda et al., 1989). Lead data from Capivari River sediments (36±53 mg/ kg) bracket those in the Frade River sediments (45 mg/ kg) (Lacerda et al., 1987), but are smaller than those reported for Acarõ River sediments (110±440 mg/kg) (Rego et al., 1993). Lead concentration in lagoon sediments (46±62 mg/kg) is similar than those from the Jacarepagua Lagoon (26±60 mg/kg) (Fernandes et al., 1993) and half of that in the Guarapina Lagoon (120 mg/kg) (Patchineelam et al., 1988). Zinc concentration in the sediments attest to the pristine character of the Capivari River watershed: values range from 100 to 142 mg/kg in the riverine environment sampling points, resembling those of the
Fig. 3. Average (O), maximum, and minimum values for hydrochemistry parameters in surface waters in Capivari River watershed (SE Brazil).
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Frade River (110 mg/kg) (Lacerda et al., 1987) and Marica Lagoon watershed sediments (96±140 mg/kg) (Barroso et al., 1991), and considerably smaller than the Zn content in the polluted Acarõ River sediments (700± 1400 mg/kg). In the lagoon Zn concentrations fall to between 60 and 87 mg/kg, while Guarapina Lagoon sediments show Zn concentrations of 110 mg/kg (Patchineelam et al., 1988) and Jacarepagua Lagoon, from 200 to 255 mg/kg (Fernandes et al., 1993). Manganese in sediments shows widely ranging values, even when compared to less impacted areas. As an example, concentrations of 96 to 196 mg/kg Mn were found in the Capivari River (this study) and 260 mg/kg in the Frade River (Lacerda et al., 1987). Again comparing the present data to that from impacted areas, lagoon values range from 279 mg/kg in the Capivari River watershed to 370 mg/kg in Jacarepagua Lagoon (Fernandes et al., 1993) and 100 mg/kg in Guarapina
Lagoon (Patchineelam et al., 1988), results probably related to the high Mn geochemical mobility in supergene environment (Rose et al., 1979). Iron shows similar concentrations for river sediments: 4.3±6.4% in the Capivari River (this study), 4.2% at Frade River (Lacerda et al., 1987), and 3.3±4.7% at Acarõ River (Rego et al., 1993). Lagoon sediment for this study have a 6.3±7.2% total Fe concentration, with 5.8% at Guarapina Lagoon (Patchineelam et al., 1988) and 6.5% at Jacarepagua Lagoon (Fernandes et al., 1993). Mangrove sediments show the largest range of values, varying from 2.5 to 5.8% Fe at the Capivari River watershed (this study) and 0.7±6.2 for mangroves in the SE Brazilian coastal region (Lacerda et al., 1989). Aluminum was not analyzed in most of the studies referred to here and is rarely mentioned in the literature. Aluminium concentrations in the lagoons therefore can only be compared with one another, and results showed
Fig. 4. Carbon at Capivari River watershed (SE Brazil). 5% error bars. (A) Total C concentration in sediments. Points 1±6=river; 7=swamp; 8A, B and C=lagoon; 9A, B and C=mangrove; 10±14=channel. (B) Carbon speciation. Points MP 01 and 02=¯uvial; MP 03=lagoon; MP 04=water channel.
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that sediments found in the Capivari River watershed (this study) ranged from 2.8 to 4.9%, far below the 8% found in Guarapina Lagoon (Patchineelam et al., 1988) and the 10% in Jacarepagua Lagoon (Fernandes et al., 1993). For these reasons, the PSBR quali®es as a `reference site' for heavy metals in sediments along the Brazilian SE coast. The heavy metal data (total concentration) from sediments determined in the chain environments (Fig. 5) show a clear horizontal evolution in response to natural inputs/outputs and biogeochemical processes.
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A general trend is apparent for all metals in the swamp site (sampling point ] 7), where a decrease in total concentrations with respect to the upstream riverine environment occurs. This decrease is partially caused by an increase in organic matter content (see Fig. 4A), which results in diluted total concentration. The authors also postulate that physico±chemical characteristics of the water in this area (i.e. low pH, EH and DO) (see Fig. 3) enhance this trend, as corroborated by Fig. 6, the stability diagram of Fe forms (modi®ed from Brookins, 1988), which includes pH and EH values from the studied basin. All sampled environments except the swamp
Fig. 5. Total metal concentration in sediments of Capivari River watershed (SE Brazil). 5% error bars.
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and the lagoon, show values covering both ®elds of metal partitioning (i.e. particulate and dissolved forms). The swamp values are restricted to that favoring the dissolved form, while those of the lagoon are restricted to the particulate ®eld. This phenomenon is also thought to be responsible for the decrease in the swamp in total metal concentration mostly of Fe, and to a lesser degree of Zn and Cu. At the lagoon (sampling points ] 8A, B and C) all metals showed a total concentration increase (Fig. 5) typical for coastal lagoons (Hart, 1982; Lacerda, 1994). Although likely to result from inherent area sedimentary characteristics, this tendency may also be a function of
reprecipitation of elements dissolved in the upstream swamp. Data from the mangrove sites plot roughly between headwater and lagoon environments, thus showing behavior representing fringe sites between terrestrial and water bodies. Total heavy metal concentrations in the channel sediments decrease from upstream to downstream sampling points, i.e. from point 10 to 14 (Fig. 5). Copper is an exception at point ]10, probably associated with local high organic content, the highest for the entire basin. From this sampling point on towards the sea, Fe, Al and Mn concentrations show a progressive decrease, promoted by dilution with incoming marine sediments,
Fig. 6. Stability ®eld diagram for Fe, adapted from Brookins (1988) including pH and EH values from environments in Capivari River watershed (SE Brazil).
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Fig. 7. Percentage of total metal concentration present as potentially bioavailable fraction, in the sediments of Capivari River watershed (SE Brazil). Points 1±6=¯uvial; 7=swamp; 8A, B and C=lagoon; 9A, B and C=mangrove; 10±14=channel.
usually low in such elements. In the middle part of the channel sediments show Pb and Zn increases, probably attributed to the so-called `maximum turbidity phenomena' (Salomons and FoÈrstner, 1984). Only Cr and Cu concentrations do not completely follow the pattern shown for the other metals; instead, an erratic Cr distribution along the channel was observed (although representing a dilution curve if sampling point ]12 is ignored). For Cu two extremely high concentration values were determined for sampling stations 10 and 14. The ®rst may be associated with high organic matter content, with the second resulting from an adjacent small elevation were the concentration is equivalent to those in the headwaters.
values than those from upstream environments. Mangrove sediments show a slight increase in concentration when compared to those from the lagoon (except for Zn). However, the pattern remains the same, i.e. Cr
4.5. Potentially bioavailable metal concentration Concentration (expressed as % of total metal concentration) of the potentially bioavailable fraction of Cr, Cu, Pb and Zn in the sediments increases from inland to the estuarine portion of the basin (Fig. 7). This is likely and the direct result of the intense estuarine zone dynamic, where tides change twice a day and ¯uvial and marine conditions, waves and currents promote resuspension of bottom materials. These characteristics aect reversible processes such as sorption/desorption, favoring the bioavailability of heavy metals and their release from particles into the water. Consequently, lagoon sediments at the estuarine zone show, for every element except Pb, larger concentration
Fig. 8. Discriminant analysis. DF=discriminant function. R=river stations; S=swamp; L=lagoon stations; M=mangrove stations; C=channel stations.
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4.6. Geochemical carriers In the present study 3 heavy metal geochemical carriers were considered: (1) mineral lattice, represented by Al; (2) Fe and Mn oxy-hydroxides; and (3) organic matter, represented by C. Carbonate, a fourth possible geochemical carrier, was discarded because of its virtual absence in Capivari River watershed sediments. Once established the 5 environmental groups, by using the data on both the total and potentially bioavailable fraction of metal and total carbon concentration from sediments representing them, a discriminant analysis identifying the variables characterizing each environment was performed (Legendre and Legendre, 1983).
Two discriminant functions were responsible for 95% of the data variation. The ®rst one (73%), like the second (22%), relate to total Fe and Al. Both functions are graphically represented in Fig. 8 for samples from river (``R''), swamp (``S''), lagoon (``L''), mangrove (``M'') and channel (``C'') environments. The left-hand side of the plot represents Al. In the river and the swamp areas the mineral lattice is the most important heavy metal carrier. The right-hand side of the diagram plots data from environments where Fe oxy-hydroxides are the most important metal transport form. These results corroborate the postulated horizontal heavy metal evolution for the studied basin. They make obvious the importance of estuarine dynamics, where upstreamordered minerals are altered and amorphous or poorly
Fig. 9. Total metal and C concentration in the sediment core extracted from the swamp site at Capivari River watershed (SE Brazil). Fe, Al and C in%. The others in mg/kg.
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crystallized forms start to predominate. However, even at the estuary a possible distinction exists among environments, represented by the second discriminant function (DF 2). The lagoon sampling points at the top of the plot relate to Al while at the bottom mangrove and channel sampling points plot close together in the Fe ®eld. Based on these results it is postulated that the lagoon is a true ecotone between land and sea where both altered and ordered mineral forms coexist. 4.7. Sediment cores Two short cores were taken from sedimentary areas of Capivari River watershed: one at the swamp (Fig. 9) and other at the lagoon (Fig. 10). Concentration pro®les
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for various metals show no enrichment or depletion trend with depth, except for C and, to some extent, Cu (Fig. 9), an expected result since no anthropogenic source metal is found in the area. At the swamp (Fig. 9), oscillations in concentration pro®les up to 10 cm in depth are likely attributable to the presence of tree and shrub rhizospheres. Root respiration promotes modi®cations in the redox state, and thus changes in metal speciation. A calculated partial correlation using these results shows that Cu signi®cantly correlates with C (a=0.01), the only case where such an association seems to occur. During a reconnaissance survey done at the PSBR by DePaula et al. (1994), lignin-derived phenol contents showed that site organic matter is composed of less degraded, and
Fig. 10. Total metal and C concentration in the sediment core extracted from the lagoon site at Capivari River watershed (SE Brazil). Fe, Al and C in%. The others in mg/kg.
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consequently more reactive, vascular material. Such a characteristic, coupled with the Cu dissolution process mentioned above, seems responsible for the observed correlation. Concentration pro®les for the lagoon are quite constant (Fig. 10); due to the absence of vegetation, no oscillations in concentrations occurred at the top of the core, a pattern again qualifying the study area as a likely `reference site'. The atmospheric Zn transport in the region, determined by Pedlowisk et al. (1991) and Silva Filho (1997) is not signi®cant when compared to the geological load described here. Coastal lagoons are good collectors for atmospheric deposition and in this study no increase in metal concentration in core top was observed. Besides, using Al concentration to normalize the Zn, the ratio shows no trend with depth, presenting a mean value of 19 and standard deviation of 2. The calculated partial correlation based on the results of analysis of the core, showed Al acting as a Zn geochemical carrier, and Fe acting as a Pb carrier during the burial of sediments in the lagoon (a=0.01). As stated above these observations reinforce the previous results characterizing the lagoon as a boundary of this system where both `continental' and estuarine processes can occur simultaneously. 5. Conclusions In spite of the intense rate of degradation in the majority of ecosystems found along the SE coast, the Capivari River watershed is surprisingly well preserved. Heavy metal concentrations in sediments from the successive ecosystems are in general lower than in those found in similar regional ecosystems. Surface heavy metal enrichments in collected sediment cores were not observed. It is therefore concluded that this site quali®es as a `reference site' for studies on the biogeochemistry and ecotoxicology of sediments from similar ecosystems along the SE Brazilian coast, principally the ``Serra do Mar'' region, stretching from Guanabara Bay in Rio de Janeiro south to the Paranagua Bay, in Parana State (Southern Brazilian coast). This portion of the country harbors most industry, shipping, and urban development. The authors believe this work will contribute to increased public awareness concerning feasible recuperation of impacted areas, through programs based on sound scienti®c knowledge. Acknowledgements The authors would like to acknowledge the help of the PSBR personnel in providing ®eld facilities. DePaula received a CAPES scholarship and A. A. Mozeto received a FAPESP research grant (No. 96/
0634-2). We also acknowledge Prof. Paula Ann Matvienko Sikar for the English revision of the manuscript, as well as the two reviewers who provided excellent contributions to the ®rst version of this work. Andre and Rafael Mozeto's (DI Design) design work with the ®gures is also greatly appreciated. References Amador, E.S. 1985. SubsõÂdios geoloÂgicos e geomorfoloÂgicos aÁ elaboracËaÄo do plano diretor da Reserva BioloÂgica Estadual da Praia do Sul. RelatoÂrio Interno. FEEMA, Rio de Janeiro. Ambuhl, H., Buhrer, H., 1975. Zur tecnick der entnahme ungestorer grosse proben von sedimenten; ein verbesserters bohrlot. Schweiz. z. Hydrol. 37, 175±186. ArauÂjo, D.S.D., Oliveira, R.R., 1988. Reserva BioloÂgica Estadual da Praia do Sul (Ilha Grande, Estado do Rio de Janeiro): Lista preliminar da ¯ora. Acta Bot. Bras. 1 (2), 83±94. Barroso, L.V., De Paula, F.C.F., Ovalle, A.R.C., Bidone, E.D. 1991. GeoquõÂmica de sedimentos ¯uviais da Bacia de Marica (RJ) como ferramenta para o gerenciamento de recursos hõÂdricos. SimpoÂsio Brasileiro de Recursos HõÂdricos, IX. Rio de Janeiro, pp. 17±26. Brookins, D.G., 1988. EH-pH Diagrams for Geochemistry. Springer, New York. DePaula, F.C.F., Oliveira, R.R., Carvalho, C.E.V., Ovalle, A.R.C., Barroso, L.V., Rezende, C.E., 1994. Pesquisa geoquõÂmica orientativa na bacia do Rio Capivari, Ilha Grande, RJ. SimpoÂsio de Ecossistemas da Costa Brasileira, 3, Anais. Serra Negra, 382±395. DePaula, F.C.F., Carvalho, C.E.V., Ovalle, A.R.C., Bernardes, M.C., Barroso, L.V., 1998. Water geochemistry in a landscape gradient in an Atlantic Rainforest environment, Ilha Grande, Southeastern Brazil. Verh. Int. Verein. Limnol. 26, 903±906. Fernandes, H.M., Cardoso, K., Godoy, J.M.O., Patchineelam, S.R., 1993. Cultural impact on the geochemistry of sediments in Jacarepagua Lagoon, Rio de Janeiro, Brazil. Environ. Technol. 14, 93±100. Fiszman, M., Lacerda, L.D., Pfeier, W.C., 1984. Comparison of methods used for extraction and geochemical distribution of heavy metals in bottom sediments from Sepetiba Bay, Rio de Janeiro. Environ. Technol. Lett. 58, 567±572. Hart, B.T., 1982. Uptake of trace metals by sediments and suspended particles: a review. Hydrobiologia 91, 299±313. Lacerda, L.D., 1994. Biogeochemistry of heavy metals in coastal lagoons. In: Kjerfve, B. (Ed.). Coastal Lagoons Processes, 8. Elsevier: Amsterdam, pp. 221±241. Lacerda, L.D., Rezende, C.E., Silva, C.A.R., Wasserman, J.C., 1987. Metal composition of sediments from mangroves of SE Braziliam coast. In: Lindenberg, S.E., Hutchinson, T.C. (Ed.). Heavy Metals in the Environments Int. Conf. New Orleans, vol. 2, pp. 464±466. Lacerda, L.D., Souza, C.M.M., Pestana, M.H.D., 1989. Trace metals geochemical associations in sediments of a non-contaminated estuary. CieÆnc Cult. 41, 301±304. Legendre, L., Legendre, P., 1983. Numerical Ecology. Elsevier, New York. Moulton, T.P., 1993. Ecologia dos rios e outros corpos de aÂgua na Ilha do Cardoso, SaÄo Paulo, Brasil. SimpoÂsio de Ecossistemas da Costa Brasileira, 3, Anais. Serra Negra, 172±191.
F.C.F. DePaula, A.A. Mozeto / Applied Geochemistry 16 (2001) 1139±1151 NIST, 1995. Certi®cate of analysis: standard reference material 1646a, estuarine sediment. National Institute of Standards Technology, Gaithersburg. Odum, E.P., 1977. Ecologia, 3rd ed. Pioneira, SaÄo Paulo. Patchineelam, S.R., LeitaÄo Filho, C.M., Kristotakis, K., Tobschall, H.J., 1988. Atmospheric lead deposition into Guarapina Lagoon, Rio de Janeiro State, Brazil. In: Seelinger, U., Lacerda, L.D., Patchineelam, S.R. (Eds.), Metals in Coastal Environments of Latin America. Springer, Berlin. Pedlowisk, M.A., Lacerda, L.D., Ovalle, A.R.C., Wats, P.P., Silva Filho, E.V., 1991. Atmospheric inputs of Zn, Fe and Mn into the Sepetiba Bay, Rio de Janeiro. CieÆnc. Cult. 43 (5), 380±382.
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Rego, V.S., Pfeier, W.C., Barcellos, C.C., Rezende, C.E., Malm, O., Souza, C.M.M., 1993. Heavy metals transport in the AcarõÂ-S.J. de MeritõÂ River System, Brazil. Environ. Technol. 14, 167±174. Rose, A.W., Hawkes, H.E., Webb, J.S., 1979. Geochemistry in Mineral Exploration, 2nd ed. Academic Press, London. Salomons, W., FoÈrstner, U., 1984. Metals in the Hydrocycle. Springer, Berlin. Silva Filho, E.V. 1997. GeoquõÂmica da DeposicËaÄo AtmosfeÂrica no Litoral do Estado do Rio de Janeiro. PhD Thesis. Univ. Federal Fluminense, NiteroÂi. Suguio, K., 1973. IntroducËaÄo aÁ sedimentologia. Editora Edgard Blucher Ltda, SaÄo Paulo.