Assessment of heavy metals in sediments and aquatic organisms in West Lake (Ho Tay), Hanoi, Vietnam

West Lake (Ho Tay) is the largest freshlake in Hanoi, Vietnam. It has a surface area of ≈ 500 ha and a total volume of >10⁷ m³, and is 1–3.5 m in depth. West Lake has been classified as needing protection because of its valuable freshwater genetic resources. Noting that it has been extensively affected by pollution, the objective of the present study was to examine the extent of heavy metal contamination of the sediments and commercially important biota in the lake. Heavy metal concentrations in the sediment from most of 24 samples in West Lake exceeded the Ontario Ministry of Environment Screening Level for chromium (Cr), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn) concentrations. Aquatic organisms from the lake also were found to be contaminated by heavy metals. The average Zn concentrations in snails and mussels tissues ranged between 174 and 415 µg g⁻¹, and the Pb concentrations between 3.5 and 5.2 µg g⁻¹. The Cu concentration in shrimp (52 µg g⁻¹) and snail (189 µg g⁻¹), and the Pb concentration in all fish species and shrimp from the lake (2.0–5.2 µg g⁻¹) exceeded the Food Standard Australia‐New Zealand (FSANZ) health standards for human consumption. The Cd concentration in Cyprinus carpio also exceeded the FSANZ standard. The implications of these study findings for the effective management of the food and ecological resources of West Lake are discussed.     

Sediment phosphorus characteristics in the clearwater state of Lake Mogan, Turkey

This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte‐dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth‐related (0–20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (–0.132 µg m^?2 day^?1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g^?1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic‐bound phosphorus (Org ≈ P) constituted 37% of the TP in Lake Mogan. The most important phosphorus‐immobilizing factors are high iron content (14 200–47 750 µg g^?1 DW), the sediment's clay content (47.80–51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510–850 individuals m^?2), which depend on sediments with high iron and low organic matter (5.42–13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long‐term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long‐term changes in the sediments of Lake Morgan must be monitored.     

Anthropogenic and seasonal influences on the dynamics of selected heavy metals in Lake Naivasha, Kenya

Lake Naivasha is a freshwater lake in the Eastern Rift Valley of Kenya (0°45′S and 36°20′E). It has no surface outlet and is perceived to be under anthropogenic stress. Being situated at the basin of the rift valley, the lake acts as a sink for wastes from the town of Naivasha and the surrounding horticultural industry. Flux experiments were conducted to investigate the dynamics of heavy metals between the sediment–water interface in Lake Naivasha. In situ benthic flux experiments were conducted at two sites, one near the municipal wastewater inflow to the lake (site SS), and one at the papyrus field near the horticultural farms (site SH). Sediment samples from the exposed riparian land were collected during the dry season after the lake has receded, and the fluxes of selected metals were determined in the laboratory under simulated conditions. Aluminium in situ benthic flux at site SS averaged 7 mmol m^?2 h^?1, and was correlated positively with pH (Pearson correlation coefficient (r) = 0.89). While the in situ benthic flux of aluminium at site SH averaged 1 mmol m^?2 h^?1. In situ benthic fluxes of copper and manganese were predominantly positive at site SS, but not at site SH. The papyrus field at site SH played an important role in buffering of the lake in regard to the selected metals investigated in this study. Redox‐sensitive metals were precipitated in the benthic flux experiment for this site.     

湖北鄂州城市湖泊底泥重金属空间分布特征与污染评价

以湖北省鄂州市某湖泊底泥重金属为研究对象,在调查和分析的基础上,采用地质累积指数和潜在生态危害指数对底泥中的重金属分布以及污染状况进行评价。结果表明:从柱状底泥纵向分布来看,该湖底泥重金属含量整体上呈现从上到下递减的变化趋势,上层底泥重金属含量最高;从空间分布上看,3个湖区重金属污染程度排序是西湖区域＞东湖区域＞中湖区域。地质累积指数评价结果显示该湖底泥重金属主要以无污染—中度污染为主,底泥中重金属污染程度的大小排序为Cd＞Zn＞Cu＞Pb＞Ni＞Cr＞Hg＞As;潜在生态危害指数法的评价结果显示底泥中As、Ni、Cu、Pb、Cr和Zn生态风险水平较低,Cd和Hg存在着不同程度的潜在生态风险,Cd的潜在生态风险最高。研究成果为该湖泊的污染调查和评价分析提供参考,并为湖泊后续的保护和水环境系统的可持续发展提供科学依据。     

Distribution of Heavy Metals in Sediments of the Detroit River

The spatial distribution of 17 metals in the sediments of the Detroit River was established using metal concentrations from a river-wide survey. The survey (1999) was based on a stratified random sampling design that divided the river into upper, middle, and lower reaches and subsequently into U.S. and Canadian sides of the river. Results based on strong extraction, using concentrated acids, revealed that the Lowest Effect Level (LEL) for As, Cd, Cu, and Hg was exceeded at more than 75% of sampling sites and the Severe Effect Level (SEL) for As at 16.2% of sites. Most of the metals were homogenously distributed throughout reaches of the river, although sites with elevated concentrations were localized mainly along the middle and lower reaches as a result of a pattern of contamination sources and geographic complexity of the river, especially a spatial/temporal variability in water flow. A comparison of the results of a strong to a weak extraction (cold 5% acetic acid, to assess metal bioavailability) revealed two groups of sediment type. The first group with a “high” weak/strong ratio (bioavailable metals; about 1 for Ca, Mg, Na and from 0.6 to 0.4 for the rest of metals) was observed at sites with low flow velocities below 0.4 m s⁻¹. The “low” ratio (non-bioavailable metals; 0.25 for Ca, Mg, Na and from 0.15 to 0.05 for other metals) was observed at sites with flow velocities greater than 0.6 m s⁻¹. The data indicate that the sediment conditions, dependent on flow distribution, regulate not only the distribution of heavy metals but also can regulate metal bioavailability.     

Organic halogen,heavy metals and biological activities in pristine and pulp mill recipient lake sediments

In order to create a basis for prognosing future intrinsic remediation potential of past pollution by pulping industry, we analyzed biochemical activities and levels of pollution in sediments dated with ²¹⁰Pb and ¹³⁷Cs. A small pristine forest lake and a pulp mill recipient area of a large oligotrophic Lake Saimaa were test sites. Sediment concentration of EOX ranged from 40 to 130 μg Cl (g d.w.)⁻¹ in the pristine lake and from 770 to 4700 μg Cl (g d.w.)⁻¹ in the pulp mill recipient area and the C:Cl (w/w) ratio of sediment organic matter ranged from 2000 to 5100 and 42 to 230, respectively. The organic matter in 10 to 20 years old pulp mill recipient sediment was mainly of waste water origin. The activity gradients of β-glucosidase, butyrate-esterase, methane oxidation potential and endogenous respiration from surface to deeper layers were less steep in polluted than in pristine sediment. Methane oxidation potential was 120 μmol CH₄ d⁻¹ (g C)⁻¹ at the sediment surface of pristine lake sediment and 26 μmol CH₄ d⁻¹ (g C)⁻¹ at the polluted site, endogenous respiration rates of the surface sediment were 670 and 310 μmol CO₂ d⁻¹ (g C)⁻¹, respectively. In the most polluted layer we found a depressed potential for methane oxidation, inhibition of phosphatase and butyratelipase activities and moderately increased induction ratio of β-galactosidase to phosphatase in the SOS-Chromotest strain E. coli PQ 37. The results suggest that at the concentrations observed these effects in the sediment were not due to heavy metals.     

Bacterial abundance on the skin,gills and intestines of Cyprinus carpio in Lake Naivasha,Kenya: Implications for public health and fish quality

Cyprinus carpio is the most important fish species in the Lake Naivasha fishery, comprising 51% of the total catch in the lake. Microflora, especially enteric bacteria of human or animal origin, are the causative agent for fish contamination and spoilage. Poor sanitation standards and poor sewage treatment and disposal methods within Lake Naivasha and its catchment pose a great threat for degrading the quality of C. carpio. The potential impact is rejection of the fish in the local, regional and international markets, risking the collapse of the Lake Naivasha fishery. This study determined the bacterial quality of water and C. carpio from three different sites within Lake Naivasha, namely Malewa River mouth, sewage discharge point and a mid‐lake site, based on plate count techniques. Physicochemical parameters characterizing the lake water also were also measured in situ. This study results indicated that both the fish and water in Lake Naivasha exhibited poor bacterial quality. All the physicochemical parameters were within the recommended range for fish culture, although they also were conducive to the proliferation of bacteria. Most of the sampling sites exhibited significant spatial variation in their bacterial abundance (P < 0.05). The sewage discharge sampling site exhibited the highest mean density values for bacterial densities and clearly degrade the quality of the fish in the lake. Proper sewage treatment, and the installation of modern sanitation facilities, is recommended to improve the bacterial quality of the fish.     

Recruitment of Heliozoa, rhizopods and rotifers from the sediments of an extremely acidic lake during spring and early summer

The goal of this study was to investigate the recruitment of zooplankton from the littoral sediment of Lake 111, an acidic lake in north‐east Germany, in April (spring) and June (early summer), and its role in coupling the benthos and the pelagic. Maximum heliozoan and rhizopod recruitment occurred in early summer from sediment cores incubated at ambient water temperatures (20°C). Conversely, recruitment of the rotifer Cephalodella sp. was highest in spring at ambient spring temperatures of 12°C. A combination of passive and active recruitment processes is likely responsible. The seasonal abiotic and biotic sediment characteristics were relatively constant and therefore not likely responsible for the observed temporal recruitment pattern. The sediment water and carbon content ranged from 20 to 50% (mean = 29 ± 6% standard deviation) and 2–12% (mean = 5 ± 2% standard deviation), respectively. Similarly, there was little variation in the chlorophyll‐a (mean = 0.2 ± 0.2 µg Chl‐a g^?1 dry weight ≡ 6.1 ± 3.9 mg Chl‐a m^?2). The in situ sediment bacterial density (0.82 × 10⁹ ± 0.26 × 10⁹ g^?1 dry weight ≡ 1.01 × 10⁹ ± 0.34 × 10⁹ cells cm^?3) was high. In contrast, the abundance of zoobenthos and their resting stages was low (< 25 individuals cm^?3, and mean of 90 ± 75 cysts cm^?3, respectively), with no temporal pattern being observed. Temperature was the only abiotic factor influencing recruitment. This study suggests that, even in relatively young, chemically extreme lakes, the benthos can play an important role in whole lake microbial processes and zooplankton community composition. Such benthic repositories of resting stages potentially provide protection against adverse environmental changes.     

Sediment distribution and accumulation in Lake Naivasha,Kenya over the past 50 years

Although surface waterbodies are water sources for socio‐economic activities and ecosystems, their functions are threatened by sedimentation. Sedimentation of lakes and reservoirs can result in a loss of storage capacity and altered water quality. The present study assessed the sedimentation status of Lake Naivasha, Kenya, based on sediment distribution and accumulation over the past 50 years, using a Bathymetric Survey System (BSS). The BSS uses multi‐frequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected with a vibe‐ coring device and dated. Sediment layers corresponding to a period of the past 20 and 50 years were identified. Sediment cores and acoustic images were subsequently used to determine sediment thickness within the lake. The collected depth data from multi‐frequency APS, and dated cores were processed in DepthPic and Surfer software. The sediment depth was extracted in DepthPic, while the sediment volume and distribution were generated from Surfer software. The results from present study indicated that sediment distribution varied from one part of the lake to another for the past 20 and 50 years. High sediment thickness observed in the south‐west and eastern parts of the lake. Between 1996–2016 and 1966–2016 periods, the maximum accumulated sediment thickness was found to be about 0.55 and 1.9 m, with an average sediment thickness of 0.25 and 0.56 m, respectively. The mean sediment load corresponding to the 1966–1996 and 1996–2016 periods was 2.78 × 10⁵ and 4.61 × 10⁵ t/year, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past. Based on the present the study, it was found that combined use of BSS, sediment cores and dating can be adopted in many lakes and reservoirs to determine sediment thicknesses even where no prior bathymetric surveys exist for comparison.     

Use of TXRF and Convectional Energy Dispersive X‐ray Fluorescence Analysis (EDXRF) to determine trace metal concentrations in waters of Nakivubo Channel and Lake Victoria

To understand better the pollution levels in the waters of the Nakivubo Channel and Lake Victoria, the concentrations of manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn) and lead (Pb) were determined using convectional Energy Dispersive X‐ray Fluorescence Analysis (EDXRF) and Total X‐ray Fluorescence (TXRF) analysis. Particulate deposits were analysed for trace metals with a convectional EDXRF spectrometer. Extracted dissolved metals contents were analysed with Total Reflection X‐Ray Fluorescence. The analyses indicated higher copper concentrations in the filtrate samples collected at the rivermouths and inshore stations than on the particulate matter. Samples from battery manufacturing industry‐1 indicated copper concentrations in the filtrate exceeding the National Environmental management Authority (NEMA) drinking water standard of 1.0 mg L^?1. Free zinc concentrations were measured for almost all the sampling sites, but at concentrations below the 3 mg L^?1 NEMA standard. High concentrations of iron in the labile form measured at the lake shores were above NEMA drinking water standards of 0.3–3.5 mg L^?1 in 2006, except for the April 2006 Murchison Bay rivermouth, and for low manganese concentrations in the lake waters. The iron and manganese concentrations on the particulate matter at the upstream end of the Channel, but were lower in the lake waters. Effluents from soap manufacturing industries exhibited elevated total iron concentrations, ranging from 19.038 ± 0.190 to 63.129 ± 6.248 mg L^?1 throughout the 2‐year study period. The manganese concentrations were the highest for the battery manufacturing industry‐2 site in April 2006. The total iron and manganese concentrations were generally higher upstream along the Nakivubo Channel than in the lake waters. Cobalt and lead concentrations were below detection limits for most of the sampling sites. Generally, most metal concentrations along the Nakivubo Channel exceeded acceptable limits, illustrating the need for mitigation measures.     

东湖沉积物中重金属垂向分布特征及污染评价

为了掌握武汉东湖的水环境状况,以沉积物为研究对象,使用电感耦合等离子体质谱仪(ICP-MS)测定了不同湖域沉积物柱状样中9种重金属(Cd、Zn、As、Cu、Co、Pb、Mn、Cr、Ni)含量,对重金属元素的垂向分布特征进行了研究,并采用地累积指数法对重金属的污染程度进行评价。结果表明:沉积物中9种重金属元素含量排序为MnCrPbZnNiCuCoAsCd;垂向分布特征为Cr、Ni的含量随沉积物深度增加而增加,Cu、As、Cd的含量随沉积物深度增加而减少。地累积指数评价表明,郭郑湖西岸污染最为严重,汤菱湖最轻,累积较为严重的是Cr、Mn、Cd和Pb,其中Cd和Pb达到中度污染程度。     

Anoxygenic phototrophic bacteria and aerobic phototrophs in Normans Lagoon, a 'billabong' adjacent to the Murray River, south-eastern Australia

The development and demise of substantial populations of bacteriochlorophyll (BChl) a and d containing phototrophs are documented within the bottom waters of a billabong (oxbow lake) in south‐eastern Australia. The observation of such populations within a freshwater body is unusual, illustrating an unexpected source of organic carbon within the floodplain ecosystem of one of Australia's principal rivers. Values of up to 1086 µg L^?1 BChl a and 490 µg L^?1 BChl d were recorded during an 11 month study of physico‐chemical parameters, algae and bacteria. An unusual density stratification was observed within the billabong, fostered by an increase in bivalent ions at depth, and leading to persistent anoxia below 0.75 m depth over summer. A marked vertical distribution was observed for both algae and bacteria, that for the bacteria being lost with a mixing event in late March. The presence of up to 74 µg L^?1 BChl a at the surface of the billabong during the summer months is ascribed to entrainment of bacteria within bubble plumes rising from the sediments.     

Comparative spatial metal concentrations and partitioning in bottom sediments of two tropical freshwater lake basins,Kenya

Metal concentrations in the water, sediments and biota in alkaline, near neutral water tropical freshwater lake basins were determined and a comparative analysis made on the spatial and accumulated trace metal concentrations, and geochemical partitioning of iron (Fe), manganese (Mn), copper (Cu), chromium (Cr), zinc (Zn), nickel (Ni), cadmium (Cd) and lead (Pb) in bottom lake sediments. Variable accumulated levels were found in the analysed sediments and aquatic biological tissues. Metal partitioning data in the present study from the two areas exhibits similar trends in magnitude. The residual fractions retained relatively higher amounts of metals. Relatively higher contents of Pb, Cr and Cu were found in Lake Victoria sediments. Cd, Ni, Mn and Pb are of concern because a higher percentage of these metals were retained in the more bioavailable fractions in Lake Naivasha. Total levels of sediment mercury were comparable for the two lake basins. Metals were found in significant levels in the tissues of aquatic organisms, highlighting the potential risks to other levels within the aquatic food chain. Although the exposure risk was not evaluated, it is important to continue monitoring these elements in fish, as sediments were found to contain considerable quantities of the metals. Numerous sediment extraction techniques data applied for evaluating metal partitioning in sediments cannot be compared because of the use of different methods. Nevertheless, the information is still useful in differentiating and understanding pollution loads from natural versus anthropogenic sources and their associated risks.     

Modeling of sediment and heavy metal transport in Taihu Lake, China

With the current rapid economic growth, heavy metal pollution has become one of the key issues in the Taihu Lake. Although heavy metal pollution levels and distributions of the Taihu Lake have previously been described, an effective model to describe the transport process of heavy metals between the water column and sediment bed for this lake is not available. It is known that heavy metals in the water column can be related to the resuspension of sediment in the lake bed. In this study, we set up a coupled model of relating hydrodynamics, sediment and heavy metals based on Environmental Fluid Dynamics Code (EFDC), and applied it to Taihu Lake, China. For calibration and validation of the model, we employed two series of field sampling data taken all over Taihu Lake during April and July of 2009. The results show that the hydrodynamics simulations of the coupled model agree with the observations reasonably well and the sediment and heavy metal model shows similar variation trends during the simulation. Our results indicate that the model can be used for simulating the sediment and heavy metal transport process in the Taihu Lake and here we provide an effective tool for water quality management at small time scales.     

Water and Sediment Quality in Lakes along the Middle and Lower Reaches of the Yangtze River, China

Water and sediment samples were collected from 45 lakes along the middle-lower Yangtze River, China. Each lake was sampled seasonally, over a period of one year. Water quality variables and metals in sediments were measured. Lakes along the lowest part of the river, within the Yangtze River Delta, had highest nutrient concentrations and were eutrophic or hypereutrophic. Lakes displayed a gradient in many water chemistry variables, from the middle to the lower Yangtze River. Lakes of the Delta region had the highest conductivity, sulfate, turbidity, and Chl-a values, and the lowest dissolved oxygen concentrations. A number of lakes near urban areas in the study region also displayed similar conditions. Lakes polluted by heavy metals were found in the upper part of the lower Yangtze River and had high Cu, Cr, and Co concentrations in sediments. The mean I_geo (index of geoaccumulation) values for Cu, Cr, and Co classes ranged from 0 to 4, indicating moderate to heavy contamination, contributed mainly from untreated industrial waste water produced within the lake catchments. Lakes of the middle Yangtze River are generally in relatively better condition, except for those around urban zones, which experience higher nutrient and heavy metal loading. The spatial distribution of lake conditions in the area can be related to the policy of regional economic development. The Delta region in China is developed and includes such cities as Shanghai and Suzhou. Heavy industries have moved into the interior region of China too, and development of modern cities is now occurring under some level of environmental protection. Nevertheless, lakes in the central part are becoming seriously polluted with both heavy metals and nutrients because local authorities promote industrialization and urbanization to improve economic conditions, while often ignoring environmental protection. Pollution is increasingly occurring in upstream reaches, a tendency that will bring more environmental problems. Interior lakes of China require immediate attention to prevent further declines in water quality.     

Trace metal concentration in water and sediments of satellite lakes within Lake Victoria (Kenya) basin

Lakes Kanyaboli, Sare and Namboyo are three important freshwater satellite lakes in the northern region of the Lake Victoria (Kenya) basin. Lake Simbi, a small alkaline -saline crater-lake is located near the southern shoreline of the Nyanza Gulf of Lake Victoria. The three freshwater lakes provide unique aquatic habitats for the important indigenous fish species and other aquatic biodiversity, as well as serving as water resources for the surrounding communities. Surface and sediment samples were collected and examined to characterize these lake systems. Metal partitioning among the various defined geochemical phases also was determined. Based on the measured concentrations, the satellite lake waters are relatively uncontaminated with regard to Al (aluminium), manganese (Mn), zinc (Zn), copper (Cu) and chromium (Cr). Levels of most elements were below detection limits, as well as being well below the desirable drinking water guideline values proposed by the World Health Organization. The exception was the elevated iron (Fe) contents (>300 μg L⁻¹). The sediments exhibited a relatively low level of contamination with regard to heavy metals. The mean values of the measured metals in the sediments were compared to levels in adjacent Lake Victoria. The study results from these poorly-studied, and relatively unperturbed ecosystems, compared to the main body of lake Victoria, highlight their importance as conservation areas, despite the small-scale fishery activity, potential threats from human activities and their sensitivity to fluctuating environmental conditions.     

Heavy metals in sediments and uptake by burrowing mayflies in western Lake Erie basin

During the past two decades, burrowing Hexagenia mayflies have returned to the western basin of Lake Erie. Because of their importance as a prey resource for higher trophic levels and their extensive residence time in potentially contaminated sediment, Hexagenia may be a source of heavy metal transfer. To better understand the distribution and transfer of heavy metals in sediment and mayflies, sediment and mayfly nymphs were collected from 24 locations across the western basin of Lake Erie in May 2007. Following USEPA protocols, samples were analyzed for 16 elements using ICP-OES or ICP-MS. Metal concentrations in the sediments exceeded the Threshold Effect Level for at least one metal at all sample sites. Sediment heavy metal distribution profiles indicate metal concentrations are correlated with organic matter content, and the highest heavy metal concentrations were found in the central deeper region of the western basin where organic content in the sediments was greatest. Hexagenia were distributed throughout the western basin, with greatest density (1350/m²) within the Detroit River plume. The Cd and Zn levels in mayflies were on average approximately 4 and 2 times greater, respectively, than sediment levels, and the Cd concentrations in the sediments exceeded the Threshold Effect Level at 27 of 28 sites and exceeded the Probable Effect Level at 9 of 28 sites. Spatial representation of heavy metal concentrations in mayflies exhibited a similar pattern to the spatial distribution of heavy metals and organic matter in the sediments with higher concentrations of metals found in mayflies residing in the central deeper region of the western basin.     

Assessment of heavy metal contamination in coastal lake sediments associated with urbanization: Southern Kerala,India

The study of the spatiotemporal variation of heavy metals in lake sediments is of great importance because heavy metals can result in toxic effects on aquatic biota through bioaccumulation. This study was undertaken to evaluate the degree of heavy metal contamination in the lacustrine sediments and the corresponding environmental deterioration in a tropical, urban, coastal lake (Akkulam–Veli), located in Kerala, India. The spatiotemporal variations of the cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) concentrations in the lake sediments, as well as various indices of anthropogenic contamination, including Contamination Factor (CF), Pollution Load Index and Geoaccumulation Index (Igeo), were used to assess the degree of contamination. This study indicated contamination of the lake sediments with Cu, Pb and Zn. Urban domestic sewage and land run‐off are the major drivers of the heavy metal loads to the lake. During the pre‐monsoon, sediment contamination occurs in the upstream portion of Akkulam Lake because of a high clay content in the sediments. During the monsoon period, Akkulam Lake and the upstream portion of Veli Lake exhibit sediment contamination owing to high silt content. Domestic sewage is the main source of copper and zinc to the lake. Sewage bypass into the drains in the lake basin is largely responsible for the copper and zinc sediment contamination. High traffic levels and wastewater discharges from service stations/workshops are the main cause of the Pb loads entering the lake. Rubber particles of vehicle tires contain zinc and copper pigments that can accumulate on the surface of busy streets, entering the drains during rainfall events. Based on these study results, the accumulation of copper, zinc and lead in lake sediment can be controlled to a great extent by restricting the above‐noted activities. As the sediment content of lead, zinc and copper is confined to the clay fraction during the non‐rainy season and to the silt fraction during other seasons, lake restoration work should largely incorporate treating the clay and silt fractions, respectively, during both the non‐rainy season and rainy season.     

Status and Trends of Benthic Populations in a Coastal Drowned River Mouth Lake of Lake Michigan

Muskegon Lake was designated an Area of Concern because of severe environmental impairments from direct discharge of industrial and municipal wastes. Since diversion of all municipal and industrial wastewater in 1973, few studies have assessed ecological changes associated with improved water quality. We examined distributions and long-term changes in the benthic macroinvertebrate community at 27 sites. Distributions were evaluated relative to distance from the river mouth, water depth, grain size, and known areas of sediment contamination. Temporal changes were assessed relative to wastewater diversion. Oligochaeta and Chironomidae dominated the community, and the oligochaete trophic condition index indicated that, in 1999, the lake was generally mesotrophic to eutrophic. Cluster analysis resulted in four distinct site groupings. A cluster of sites near the river mouth had the highest total density (9,375 m⁻²) and lowest diversity (Shannon Weaver Index 1.05) suggesting an enriched habitat. A site cluster in the south central region had the lowest oligochaete density (2,782 m⁻²), lowest oligochaete trophic condition index scores (1.00), and highest diversity (2.24), suggesting the best habitat. The chironomid community in this site cluster was dominated by predatory species, possibly resulting from high concentrations of heavy metals at some sites. Densities of all major taxonomic groups increased significantly between 1972 and 1999. Decreasing proportions of oligochaetes (0.85 to 0.68) and increasing diversity suggest improved environmental conditions over this period. Evidence suggests that changes in Muskegon Lake's benthic community were more a result of wastewater diversion than Dreissena invasion.     

珠江长州断面底泥重金属污染潜在生态危害评价

测定了珠江广州河段长州断面底泥中重金属镉、铬、铜、铅的质量比,采用Tessier形态分类法对它们在底泥中的存在形态进行了提取和测定。监测分析表明,该断面底泥中镉、铬、铜、铅质量浓度均高于全国湖泊底泥中的平均值。该断面底泥中镉、铬、铜、铅质量比分别为广东土壤背景值的49.50倍、3.62倍、14.24倍、5.51倍,底泥成为这些重金属的富集地。镉以可交换态为主,占总量的比例为47.47%;铬和铅以残渣态为主,占总量的比例分别为42.35%和47.28%;铜主要以有机态及硫化物结合态为主,占49.06%;残渣态较低,占18.26%。采用潜在生态危害指数法对该断面底泥中的镉、铬、铜、铅进行了潜在生态危害评价,结果表明:镉潜在生态危害强,铬、铜、铅的潜在生态危害轻微。