Concentrations In Surface Sediments Research Articles

Heavy metal contamination in western Xiamen Bay sediments and its vicinity, China

Concentrations of selected heavy metals (Cu, Pb, Zn, Cd, Cr, Ni and Fe) in surface sediments from nine sites in western Xiamen Bay and its vicinity were studied in order to understand current metal contamination due to urbanization and economic development in Xiamen, China. The sediment samples were collected in December 2004 and July 2005 respectively in order to examine temporal variations. In this study, we found that heavy metal concentrations in surface sediments sampled in the western Xiamen Bay and adjacent Maluan Bay and Yuandang Lagoon varied from 19 to 97 mg kg −1 for Cu, 45 to 60 mg kg −1 for Pb, 65 to 223 mg kg −1 for Zn, 0.11 to 1.01 mg kg −1 for Cd, 37 to 134 mg kg −1 for Cr, 25 to 65 mg kg −1 for Ni and 3.08 to 4.81% for Fe. Although all metal concentrations in sediments meets Chinese National Standard Criteria for Marine Sediment Quality, both metal enrichment factors (EF) and geoaccumulation index ( I geo) show that Pb contamination exists in the entire study area and contamination of other metals are also present in some locations depending on the sources, of which sewage outlets and commercial ports are the main sources of contaminants to the area. This study shows that using the sediment quality standard criteria only to assess sediments cannot properly reflect sediment contamination. A multiple approaches should be applied for the sediment quality assessment.

Landscape-scale patterns of sediment sulfur accumulation in Swedish lakes

Sulfur has played a central role in the acidification of many lakes in Scandinavia and other regions. As part of the research into sulfur cycling, numerous studies have analyzed the sediment record in order to develop insights into past in-lake cycling of sulfur, particularly in the context of reconstructing past deposition rates. Although many of these studies have shown that it is not easy to interpret the sediment record in terms of past sulfur deposition rates, analyses of sulfur in sediment still provide valuable information on the response of lakes to anthropogenic sulfur deposition. Here, we have analyzed sulfur in top and bottom samples from short surface cores (25–35 cm, representing ≥250 years) as well as bulk cores from ∼110 lakes located throughout Sweden, which were collected during 1986, as well as in more-detailed profiles from six lakes. The lakes with the highest surface sediment concentrations (9–24 mg S g−1 dry mass) and the highest calculated inventories of ‘excess’ sulfur (20–180 g S m−2) are found in southern Sweden and around one industrial area along the northeastern coast where sulfur deposition rates and lake-water concentrations have been highest. For many lakes in the central and northern inland region it is common that the sediment cores exhibit either no enrichment or even a decline in sulfur concentrations in near-surface sediments, which we suggest was the pre-pollution norm for lakes. Although interpreting sulfur sediment profiles is problematic for reconstructing deposition, a more-comprehensive spatial sampling approach shows that there is a good geographic agreement between sulfur deposition, lake-water chemistry and sediment sulfur accumulation.

Water geochemistry and sedimentary pigments in northern Victoria Land lakes, Antarctica

Total concentrations of algal pigments, organic C, C, N, P and S were determined in surface sediments from the littoral zone of 21 lakes in ice-free areas of northern Victoria Land (Antarctica) with different climatic and environmental conditions. Concentrations of major ions and nutrients were also determined in water samples from the same lakes. The latter samples had extremely variable chemical compositions; however, all the lakes resulted oligotrophic. Pigment concentrations in surface sediments were comparable to those reported for other Antarctic lakes and lower than those in oligotrophic lakes at lower latitudes. Cyanophyta, Chlorophyta and Bacillariophyta were the main taxa identified. These taxa correspond to those reported in previous microscopy-based studies on Antarctic phytoplankton and phytobenthos. Discriminant Function Analysis and Canonical Correspondence Analysis of data indicate that the distribution of pigments in these Victoria Land lakes depends mainly on their geographical location (particularly the distance from the sea) and nutrient status.

Seasonal dynamics and decadal changes of benthic foraminiferal assemblages in the western Baltic Sea (NW Europe)

Abstract. Living benthic foraminiferal assemblages were monitored between January and July 2004 in the Kiel Bight, Baltic Sea. Phytoplankton blooms and the deposition of organic detritus were depicted by fluorometer hydro casts and pigment concentrations in surface sediments. Three depositional pulses of organic matter were identified by high phytoplankton concentrations above the sea floor and elevated pigment concentrations in the surface sediment. The foraminiferal assemblage composition remained rather constant but the population density of Elphidium excavatum clavatum showed a two- to six-fold increase within a few days after organic detritus deposition. The foraminiferal assemblage composition was compared to earlier studies in this area. Elphidium excavatum, Ammotium cassis and E. incertum dominated the living fauna in the 1960s and 1970s. The recent survey revealed a predominance of E. excavatum subspecies (more than 90% of the living assemblage). The average population densities were six times higher than in the 1970s. Data structure and model calculations suggested that E. excavatum clavatum is able to reproduce rapidly, with high offspring numbers at elevated food supply. The diminution of A. cassis has occurred in Kiel Bight during the last ten years and was most likely induced by a period of low deep-water salinities in the early 1990s.

50-year record and solid state speciation of mercury in natural and contaminated reservoir sediment

Contaminated fluvial sediments represent both temporary sinks for river-borne pollutants and potential sources in case of natural and/or anthropogenic resuspension. Reservoir lakes play a very important role in sediment dynamics of watersheds and may offer great opportunities to study historical records of river-borne particles and associated elements transported in the past. The fate and potential environmental impact of Hg depends on its abundance, its carrier phases and its chemical speciation. Historical Hg records and solid state Hg speciation were compared in sediments from two contrasting reservoirs of the Lot River (France) upstream and downstream from a major polymetallic pollution (e.g. Cd, Zn) source. Natural (geochemical background) and anthropogenic Hg concentrations and their relationships with predominant carrier phases were determined. The results reveal important historical Hg contamination (up to 35 mg kg −1) of the downstream sediment, reflecting the historical evolution of industrial activity at the point source, i.e. former coal mining, Zn ore treatment and post-industrial remediation work. Single chemical extractions (ascorbate, H 2O 2, KOH) suggest that at both sites most (∼75%) of the Hg is bound to organic and/or reactive sulphide phases. Organo-chelated (KOH-extracted) Hg, representing an important fraction in the uncontaminated sediment, shows similar concentrations (∼0.02 mg kg −1) at both sites and may be mainly attributed to natural inputs and/or processes. Although, total Hg concentrations in recent surface sediments at both sites are still very different, similar mono-methylmercury concentrations (up to 4 μg kg −1) and vertical distributions were observed, suggesting comparable methylation-demethylation processes. High mono-methylmercury concentrations (4–15 μg kg −1) in 10–40 a-old, sulphide-rich, contaminated sediment suggest long-term persistence of mono-methylmercury. Beyond historical records of total concentrations, the studied reservoir sediments provided new insights in solid state speciation and carrier phases of natural and anthropogenic Hg. In case of sediment resuspension, the major part of the Hg historically stored in the Lot River sediments will be accessible to biogeochemical recycling in the downstream fluvial-estuarine environment.

Interpretation of anthropogenic input of metals in the South China Sea bottom sediments off Terengganu (Malaysia) coastline using Al as a reference element

The metal concentrations in surface sediment of the South China Sea off the Terengganu coastline were determined. Cu, Cr and Zn concentrations were comparable to values for offshore regions of the South China Sea and of concentrations of coastal sediments from the more developed west coast of Malaysia. Direct comparisons with earth crust values for Cd and Pb ratios to Al indicate anthropogenic pollution by these metals. As the sediments of the area studied are composed of significant proportions of quartz and carbonate, from shells and coral, direct ratioing to Al would result in anomalous values. Thus enrichment factor (EF) values using Al as a reference element were determined and showed that sampling sites off the major rivers of Terengganu were anthropogenically influenced by Pb and Cd. Sources of pollution are probably sewage, agricultural wastes and atmospheric deposition of Pb from the use of leaded petrol.

Depositional conditions and organic matter distribution in the Bornholm Basin, Baltic Sea

Information on grain-size distribution and total organic carbon (TOC) content of surface sediment and cores from the Bornholm Basin, together with dating of cores using the 210Pb method and shallow seismic chirp profiling, has been analysed to elucidate long-term accumulation patterns. The presence of non-depositional areas with lag sediments and low TOC content below the wave base indicates that inflows of dense bottom water originating in the North Sea and associated near-bottom currents have strong influence on the depositional patterns of bulk sediment and organic matter in this deep basin. The general fining in mean grain size towards the northeast corresponds to the direction of inflow currents and prevailing winds. Recent and previously found 210Pb-based mean accumulation rates vary greatly within the basin, between 129 and 1,144 g m−2 year−1. The accumulation rate may vary by a factor of three even between stations located only 3–4 km apart. Rates recorded close to a seismic profile are consistent with the variation in Holocene sediment thickness. This variation reflects a depositional system controlled by near-bottom inflow currents, consisting of a large-scale channel and a wedge-formed sediment package. The spatial variation in TOC content depends partly on water depth, presumably due to generally poorer degradation in the deepest part of the basin because of less frequent oxygen supply by inflow water. Moreover, there is a tendency of higher TOC contents in the southern part of the basin, which may be due to the input of sediments originating from the Oder River. Compared to values for the central, deep Baltic Sea, TOC contents show lower values of 4–6% and insignificant temporal variations. This may be due to the Bornholm Basin being located much closer to the source of the more oxic inflow water, resulting in more favourable degradation conditions.

Seasonal variation of monomethylmercury concentrations in surface sediments of the Tagus Estuary (Portugal)

Surface sediments (0–2 cm) were collected at 40 sites along the Tagus Estuary in July and December 2004. The sediments were analysed for total mercury, monomethylmercury (MMHg) and interpretative parameters (e.g. redox potential, pH, C org). No significant differences in total Hg, pH, Al, Fe, Mn and C org were found between sediments collected in the two periods, but MMHg concentrations were higher in July. On average sediments were warmer and more reducing in summer. On the basis of these results, an increase of 7 kg of MMHg (+37%) in surface sediments of the Tagus Estuary was estimated. Presumably higher temperatures in summer promote the increase of microbial activity and higher methylation rates. The alterations observed in this study point to the potential importance of seasonal changes in MMHg production at surface sediments with eventual changes in the MMHg uptake by benthic invertebrates and other organisms in the food web.

Heavy metals in sediments as evidence for recent pollution and quasi-estuarine processes: an example from Lake Druzno, Poland

This article presents the results of a geochemical investigation of sediments from Lake Druzno (northern Poland), a reservoir fed by freshwater from the catchment, with periodic input of brackish water from Vistula Lagoon. This study analyzed the spatial variation in heavy metal content in surface sediments as well as the temporal changes in metal content in two sediment cores dated using the 210Pb method. In the surface sediments, the highest metal concentrations were recorded in the northern part of the lake, with lower concentrations in the central and southern parts. Absolute values of metal concentrations in the cores were low, but normalization with respect to Al showed an increase during the second half of the 20th century. Mean enrichment factors (EF) in sediments from the second half of the 20th century ranged from insignificant (1–1.2) for Fe to (1.55–3.3) for Cu, Cd, Pb and Zn. The sediments deposited before 1950 had lower EF values (>1.5) and had low variability. Results from both the surface sediments and the cores indicate that the main source of lake pollution is brackish water intrusion from the Vistula Lagoon via the contaminated River Elbląg.

Temporal and spatial distribution of pbysirnchemical characteristics and nutrients in sediments of Lake Taihu

在不同季节,采集太湖梅梁湾和贡湖湾沉积物柱状样,研究沉积物Eh、pH、总氮、总磷以及有机质四季垂向部面分布变化特征.研究结果表明,在表层下(0-3cm).Eh随沉积物深度的增加迅速下降,很快进入还原状态.沉积物剖面上pH变化幅度不大,在6.4-7.8之间,冬季沉积物pH均有所降低.太湖沉积物中含有丰富的营养盐,总氮和总磷最高浓度分别为2.68和0.864 mg/g,其剖面分布特征表明,沉积物表层总氮和总磷含量远高于底层,其含量随深度增加而降低,但四季变化趋势不明显.沉积物中有机质含量在10 cm以上变化幅度较大,随着沉积物深度的增加,有机质含量明显减少,季节变化幅度不大.比较不同采样点发现,位于梅梁湾生态系统试验区内的S1位点沉积物氮磷内源负荷最大.;Three sites were selected for samples in Lake Taihu to observe temporal and spatial distribution of redoxpotential(Eh),pH, total nitrogen (TN),total phosphorus (TP) and organic matter(OM) in sediments. Belowthe surface of sediments Eh declined rapidly with the increase of sediment depth and it was under anaerobic condi-lion except the top layer of sediment. pH value changed silightly in the profile of sediments, which ranged from 6. 4to 7. 8. With a comparison between four seasons, p.H value was the lowest in winter. TN and TP concentrations insediments of Lake Taihu were higher, and the maximum concentrations reached 2. 68 mg/g and 0. 864 mg/g. respectively. Their vertical profiles showed that TN snd TP concentrations in surface sediments were much higherthan in deeper layers and decreased steeply with the increase of the depth on the top 15 cm of sediment layers. OMconcentrations declined rapidly al the top 15 cm of sediment layers, but there was little change in four seasons. Thesediment loads of TN and TP were much higher at Sl than that at other sites.

Characteristics of nutrients distribution from recent sediment in Lake Nansihu

对南四湖不同湖区20个表层沉积物和独山湖湖区沉积岩芯中营养元素进行了分析。结果表明表层沉积物中南阳湖总磷最高, 独山湖次之;独山湖总有机碳和总氮含量最高, 南阳湖次之;而昭阳湖总有机碳、总氮和总磷含量较低。沉积岩芯中¹³⁷Cs数据表明南四湖独山湖区柱状沉积物上部（0-18cm）沉积速率为3.5mm/a;总有机碳、总氮和总磷含量主要集中在沉积岩芯0-8cm内, 并呈现一致的垂向分布规律, 具有明显的三阶段分布特征, 反映了流域社会经济的发展导致营养元素的释放量增加, 造成了湖泊现代沉积物中营养元素的积累。碳氮比值处于7.6-11.4之间, 有机质的选择性分解不明显, 指示沉积物中有机质主要来自无纤维柬的陆源植物。监测数据表明济宁市的城市生活污水、工农业废水排放进入南阳湖是南四湖有机质和TP富集的主要来源。;Nutrients concentrations in surface and core sediments from Lake Nansihu were investigated. The results showed that sediments from Lake Nanyanghu had significantly higher TP concentrations than any other area of Lake Nansihu. Lake Dushanhu had from the highest TOC and TN content. Lake Zhaoyanghu had low TOC, TN and TP concentrations. The method of ¹³⁷Cs dating was used to derive accumulation rates of 3.5mm/a for Dushanhu Lake. The historical profiles of Dushanhu Lake showed that TOC, TN and TP mainly enriched in 0-8cm, and presented simultaneously changeable trends. The development of the Basin society and economy had resulted in nutrients release increasing, which made nutrients accumulation in recent sediment. C/N ratios varied slightly. They are 7.6 and 11.4 for the recent core. These characteristics suggested that organic matters in the sediments mainly originated from continental plants without cellulose and reserved variations in ecosystems resulted from continents. The monitored data indicated that the discharge of domestic, industry and agriculture from the lake basin directly into Nanyanghu Lake was the mainly source that made the enrichment of TOC, TN and TP in Lake Nansihu.

Effectiveness of hydrated lime and artificial zeolite amendments and sedum (Sedum sediforme) plant cover in controlling soil erosion from an acid soil

There are over 350 different species of sedum (Sedum spp.) and most of them can tolerate harsh conditions including very cold to hot temperatures, drought, and poor and stony soil. Sedum plants are used in rock gardens and edging flower beds, and for greening the tops of buildings, cottages, and thatched roofs. However, little is known about the effectiveness of sedum as vegetation cover in protecting soil erosion from a road embankment made of acid soil. Acid soil is believed to be vulnerable to soil erosion and is not suitable for plant growth. Liming treatment is required first before revegetation to alleviate the soil acidity; however, lime incorporation may affect the soil physical properties and, consequently, runoff and sediment generation. A rainfall simulation study was conducted to test the effectiveness of hydrated lime and artificial zeolite as amendments and Sedum sediforme (Rupestria group) as vegetation cover in controlling soil erosion from an acid soil taken from mountain cuts in Yamaguchi prefecture, Japan, where it is used for road embankment. The soil was treated with 0.5% lime and 10% zeolite. Two rainfall intensities of 30 and 60 mm/h were tested for 2 and 1 h, respectively, on sedum-growing soil plots measuring 0.50 by 0.30 by 0.05 m. Three levels of vegetation cover (bare soil, 25%, 75%) of sedum plant of 5-month growth under 2-day irrigation intervals were tested. The incorporation of hydrated lime and artificial zeolite amendments improved wet aggregate stability, which contributed to significant decrease in surface runoff, sediment concentration, and total soil loss by rain splash from the bare soil. Zeolite was more effective in promoting plant growth than the lime treatment; as a result the decrease in sediment generation and soil loss by rain splash, compared with the control, was larger with zeolite than with lime. Under both intensities of simulated rain, the sediment concentration and total soil loss by rain splash decreased significantly (P < 0.05) with increasing surface cover. The correlation between cumulative soil loss (CSL) and cumulative surface runoff was linear and significant (P < 0.001) and the slope coefficient decreased with increasing surface cover. This suggests that the sediment carrying capacity or the erosivity of the surface runoff was constant and it decreased with increasing surface cover. The sedum cover reduced the CSL up to 72 and 79% under 30 and 60 mm/h rainfall intensities, respectively. The mean weight diameter of the soil sediment transported by runoff and soil loss by rain splash were significantly increased, and therefore, the silt and clay proportion of the crust material formed on the soil surface decreased up to 6 and 16% under 25 and 75% vegetation cover, respectively. These results demonstrate that hydrated lime and artificial zeolite could be used as amendments and sedum plant as vegetation covers in controlling soil erosion from an acid soil.

Seasonal Variability of Heavy Metals in Surface Sediment of Lake Sapanca, Turkey

Lake Sapanca is exposed to heavy urbanization and industrialization because of its natural beauty and its proximity to the metropolitan Istanbul, Turkey. In this study, it was aimed to investigate seasonal changes of some heavy metals (Pb, Cr, Cu, Mn, Ni, Zn and Cd) concentration of surface sediment. Nine different stations were chosen as sampling points. Samples were taken every three months and the seasonal and annual average concentration of the elements were determined. Seasonal highest values of heavy metals were observed as follows; Cr, Cu, Mn, Ni and Zn in Summer, Cd in Autumn. There was no seasonal difference for Pb, Cr and Cd. It seems that Lake Sapanca has not been polluted yet. However, it was found that Cu and Ni concentrations in surface sediment exceed lowest effect level.

Distribution of Mercury and Monomethylmercury in Sediments of Vigo Ria, NW Iberian Peninsula

Fifty four samples of surface sediments (1-cm of thickness) and a gravity core of 154-cm long were collected in the Vigo Ria, NW of Iberian Peninsula. In the laboratory the sediments were oven dried at 40°C, desegregated, homogenised and analyzed for total Hg, monomethylmercury (MMHg), Al, and particulate organic carbon (POC). Mercury in sediments varied within a broad range: 0.09 to 8.9 nmol g−1 the higher concentrations being found in the shipyards and docks areas of Vigo port (southern–middle Ria zone). No correlation was found between Hg and POC. The good exponential correlation between total Hg and Al levels suggests that Hg is closely associated with the fine fraction of sediments. Monomethylmercury concentrations in surface sediments ranged between <1.4 (DL) and 8.5 pmol g−1 being the spatial distribution similar to that observed for total Hg. The lack of correlations MMHg–Al and MMHg–POC suggests that in situ processes of methylation/demethylation are responsible for MMHg distribution rather than the sediment characteristics. Additionally, these processes appear mercury-dependent only for Hg concentrations above 2.5 nmol g−1. On the basis of these results it was estimated that 155 kg of Hg (0.1% MMHg) are present in the surface sediments of Vigo Ria, being 61% of anthropogenic origin.

Levels of tin in core sediments along the Alexandria Coast, Egypt

Tin concentrations were determined in surface and core sediments from three hot spots along the Alexandria coast, namely: Abu-Qir Bay, Eastern Harbour, and Western Harbour. The mean concentrations in surface sediment were 2.434, 3.212, and 5.572 μg/g dry weight for Abu-Qir Bay, Eastern Harbour, and Western Harbour, respectively. A sharp decrease in tin level in core sediments with depth was observed in almost all locations except for core 4 in Abu-Qir Bay and core 17 in the Eastern Harbour, where the sub-sample at the 5 cm level recorded the highest tin concentrations.

Characterization and Source Assessment of Heavy Metals and Polycyclic Aromatic Hydrocarbons (PAHs) in Sediments of the Fosu Lagoon, Ghana

The first results ever obtained on polycyclic aromatic hydrocarbon (PAHs) concentrations in the Fosu lagoon surface sediments are presented together with corresponding heavy metal (Fe, Mn, Cd, Zn and Ni) concentrations. Samples collected on a monthly basis from November 2003–April 2004 (Heavy metals) and December 2003–January 2004 (PAHs) at 8 locations, representing different anthropogenic sources of contamination to the lagoon, were analyzed. Concentrations of Cd and Ni in the lagoon sediment suggest greater contamination to the lagoon from industrial activities in the vicinity of the lagoon; 50% of the sediment samples exceeded some established sediment Cd guidelines for the protection of aquatic lives. Then, 15 PAHs were detected among the sediments from the different locations and the compositional pattern in decreasing order was 3-ring > 5-ring > 4-ring > 6-ring > 2-ring PAH compounds. Σ PAH concentrations in the sediment samples ranged from 254 to 558 mg/kg, with a mean of 359.4 mg/kg. Two distinct areas were identified to be a major source of anthropogenic load of both heavy metals and PAH; the mechanical shop in the northeastern sector of the lagoon is the main location for the input of Cd and it's associated PAH compounds (e.g., acenapthylene, acenaphthene, naphthalene and benzo[a]fluoranthene) and to a lesser extent Ni. Both combustion and petroleum sources may account for PAH loads from this area. The residential area in the northern sector is responsible for high loads of Mn and its associated PAH compounds (e.g., phenanthrene, benzo[a]pyrene and anthracene). These chemicals seem to enter the lagoon mainly by the combustion of especially wood or coal.

Environmental biogeochemistry of mercury in Antarctic ecosystems

Polar regions are recognized as important sinks for long-range transport and deposition of Hg derived from natural and anthropogenic sources at lower latitudes. In previous studies we found enhanced Hg accumulation in soils, mosses and lichens from ice-free areas of Victoria Land facing the Terra Nova Bay coastal polynya. This study extends research to the distribution of organic C, total N, S, Hg, Al and Fe in surface soils, cyanobacterial mats and short sediment cores from four lacustrine ecosystems, each with different environmental characteristics and varying distances from the polynya. Results show that planktonic and benthic mats from lakes, along with mosses in the watershed, are the main sinks for Hg in summer meltwater. The C-normalized Hg concentrations in short sediment cores were higher in samples from lakes more exposed to marine aerosols from the coastal polynya. Reactive halogens in the aerosol promote the oxidation and deposition of atmospheric Hg in coastal ecosystems. The analysis of sediment cores did not reveal increasing Hg concentrations in recent sediments, except in the Lake 14 at Edmonson Point. The latter ice-free area is unaffected by the polynya and the increase in Hg concentrations in surface sediments could be due to local changes in lake water level and S biogeochemistry. Although change in sea ice coverage may enhance the role of Antarctic coastal ecosystems as sink in the global Hg cycle, our results seem to exclude possible risks for Antarctic terrestrial and freshwater organisms.

Metal concentrations in surface sediments of Paraíba do Sul River (Brazil)

The Paraiba do Sul River is located in a strategic region between the most important urban and industrial centers of Brazil. In the last years, an increase in the water pollution has been reported, caused by the untreated domestic sewerage of the inhabitants, effluents discharged by various industries, mining activities and sand extraction from the riverbed. This work used total reflection X-ray fluorescence with synchrotron radiation (SRTXRF) to determine metals in the bioavailable and residual fractions from the surface sediments. The metals identified were Ti, Cr, Mn, Fe, Cu, Zn, Rb, Sr, Ba and Pb.

Organic matter and benthic metabolism in Lake Illawarra, Australia

Carbon and nitrogen contents (total organic carbon and total nitrogen), chlorophyll-a concentrations in surface sediments and benthic sediment–water fluxes of oxygen and carbon dioxide were investigated at five stations in Lake Illawarra (Australia) to compare the sources/quality of sedimentary organic matter and the characteristics of diagenesis and benthic biogeochemical processes for different primary producers (e.g., seagrass, microphytobenthos and macroalgae) and/or sediment types (sand or mud). The unvegetated sediments showed lower C/N ratios (with the lowest value occurring in the deep organic-rich muddy site) than the seagrass ( Ruppia or Zostera) beds, which may be due to the contribution of microalgae (mainly diatoms) to the sedimentary organic matter pool. This was also supported by the detection of microalgal pigments in the bare sediments. On an annual basis, seagrass beds exhibited the highest gross primary productivity (O 2 or TCO 2 fluxes), while the lowest rates occurred in the deep central basin of the Lake. Seasonally, there was a general trend of highest production in spring or summer, and lowest production in winter or autumn. Organic carbon oxidation scenarios, evaluated by either calcium carbonate dissolution or sulfate reduction models, indicated that both models can explain organic matter mineralization. Trophic status was evaluated using different indices including benthic trophic state index, net O 2 fluxes and P/ R ratios for Lake Illawarra, which led to similar trophic classifications in general, and also the same trends in spatial and seasonal variations. Overall, these data indicated that the Lake was heterotrophic on an annual basis, as the total community carbon respiration exceeded production, and this supported an earlier LOICZ mass balance/stoichiometric modelling conclusion.

Copper, zinc and cadmium in marine cage fish farm sediments: An extensive survey

The diet of cage-farmed Atlantic salmon contains a range of trace metals, some of which have toxic properties, e.g. zinc, copper and cadmium. A survey of metal concentrations (ICP-MS analysis) in surface sediments of ca. 70 stations was carried out in both May and December 2000 around a Scottish fish farm. Additionally, at 13 stations on 2 orthogonal transects centered on the farm, sediments were analysed at 1 cm intervals to 8 cm depth. Maximum concentrations in surface sediments were 921, 805 and 3.5 μg g −1 for Zn, Cu and Cd, respectively, and were found at stations near the fish farm. The calculated losses from the farm (feed input minus fish output) were 87.0%, 4.3% and 14.0% of the background-corrected inventories for Zn, Cu and Cd, respectively, indicating that for Cu and Cd at least, the feed is not the only source.