鱼类在TDG过饱和含沙水体中的耐受性

为探讨高坝泄洪引起的总溶解气体(TDG)过饱和含沙水体对鱼类的影响,以岩原鲤和鲢鱼为研究对象,开展TDG过饱和含沙水体对不同鱼类的急性暴露试验,根据鱼类受TDG过饱和含沙水体胁迫后的异常行为和死亡率、半致死时间等指标来分析不同鱼类受胁迫后的耐受性和差异性。试验结果表明:试验初期,试验用鱼出现较明显异常行为和气泡病症状,且岩原鲤早于鲢鱼;相同TDG饱和度下,随着含沙量的增加,试验用鱼半致死时间缩短,且岩原鲤半致死时间短于鲢鱼,表明鲢鱼比岩原鲤具有更强的适应能力和耐受能力;当TDG饱和度较高时,即使含沙量低,也会造成试验用鱼的大量死亡;过饱和TDG是导致试验用鱼死亡的主要原因,但不能忽略泥沙对试验用鱼死亡的促进作用。     

Experimental study on acute impacts of hyper-concentrated flow on Gymnocypris Eckloni and implication for sediment management

Significant increases in suspended sediment concentration (SSC) always occur during dam removal or sediment flushing processes, which could result in acute impacts on aquatic organisms. An analysis of the potential impact of the Huangheyuan hydropower dam removal on the upper reaches of the Yellow River is required for adaptive management. But the reports on the impact of high SSC on fishes living in rivers in the plateau areas are limited. Further studies on impact factors, fish behavior, and assessment methods were performed in this paper. The acute response of a typical fish, Gymnocypris eckloni, was tested by experiments with sediment concentrations ranging from 3.3 × 10³ to 80.78 × 10³ mg·L⁻¹. The changes in fish aquatic surface respiration (ASR) behavior were analyzed under different SSCs. The cluster analysis of the environmental factors was conducted to analyze the relationship between the factors and fish mortality. The severity of ill effects (SEV) model was improved to assess the acute impact on fish. The results indicated that the SSC was the most related factor. The ASR could be induced by the SSC higher than 21 × 10³ mg·L⁻¹, and fish mortality was caused by SSC higher than 55 × 10³ mg·L⁻¹. The thresholds of SSC and exposure duration for fish protection were proposed to be less than 55 × 10³ mg·L⁻¹ and 6 hr, respectively. The findings could support the planning and regulation of dam sediment management on plateau areas.     

Suspended sediment effects on walleye (Sander vitreus)

Environmental windows are seasonal restrictions imposed on dredging operations in the Great Lakes and other waterways of the United States. Such restrictions often generically assume that sediments resuspended by dredging result in adverse impacts to fish; this is the case in western Lake Erie where the environmental window was established due to potential impacts on walleye (Sander vitreus). To address this concern, laboratory studies mimicking sediment resuspension during dredging operations in western Lake Erie were conducted to determine whether suspended sediments affect walleye eggs and fingerlings. Newly laid eggs and 45- to 60-d old fingerlings from separate hatcheries were exposed for 72-h under flow-through conditions to 0, 100, 250, and 500 mg/L total suspended sediment (TSS). Fingerlings, eggs, and newly hatched larvae were analyzed for multiple lethal and sublethal endpoints. Data indicated no significant effects of suspended sediment on egg hatch success or fingerling survival after three days of exposure. No significant differences were observed when comparing percent egg viability in the control with any TSS treatment; however, a downward trend was observed at 500 mg/L. No significant differences were observed during comparisons of fingerling gill lamellae in the control with any TSS treatment; however, a statistically significant difference was observed when comparing gill lamellae in the control with the original supply animals. No significant differences were found between control means and unexposed eggs or any TSS treatment. These effect data for walleye will serve to better inform the setting of environmental windows for this species in western Lake Erie.     

Accumulation and Transport of Sediment Metals by the Vertically Migrating Opossum Shrimp,Mysis relicta

This study examined the accumulation of metals (Al, As, Cd, Cu, Cr, Fe, Ni, V, and Zn) in the opossum shrimp Mysis relicta from sediments to understand the contribution of sediment metals to overall body burden metal contents. Metal biota-sediment accumulation factors, tissue depuration ratios, and sediment metal assimilation efficiencies were calculated to examine the extent to which mysids accumulate metals from sediments contained within their guts. Results were then used to estimate the concentrations of metals transported to the water column and to fish because of mysid diel vertical migration. Results showed that Al, Cr, Fe, and V were readily depurated (34 to 73% of total body burden) and were not preferentially accumulated in mysid tissues (Biota Sediment Accumulation Factor, BSAF < 0.009). In comparison, As, Cd, Cu, and Zn were not readily depurated (9 to 26% of total body burden) and were more readily accumulated in mysid tissues (BSAF > 0.037). Nickel shows an intermediate behavior for depuration and accumulation. Calculations suggest that following 12 hours depuration through vertical migration, about 1.57 μg sediment/mysid (0.05% of dry weight of M. relicta) remained as gut contents. As a result, 16 to 50% of the Al, Cr, Fe, Ni, and V and 1.0 to 5.5% of the As, Cd, Cu, and Zn mysid body burden metal content transported to the water column was attributed to sediment in the gut. These results indicate that trace metals (As, Cd, Cu, and Zn) ingested from sediments are poorly accumulated in mysids (calculated AEs ranged from 0.07 for Cr to -11 for Cu) and metals transported by mysids to fish in the water column are primarily associated with mysid tissues.     

小浪底水库排沙对下游鱼类的影响研究

采用现场调查和室内实验相结合的方法研究了黄河小浪底水库排沙期间下游河流出现鱼类死亡现象的原因。2010年度小浪底水库排沙期间,下游出现了高含沙水流过程,伴随出现了鱼类死亡现象,调查发现受影响鱼类有5目5科11种。水库排沙期间的含沙量、溶解氧变化过程的现场调查及室内实验结果表明,小浪底水库排沙时细颗粒泥沙含量较高,堵塞和损坏鱼鳃是导致鱼类死亡的原因之一。当含沙量大于80 kg/m3时,水体溶解氧下降至鱼类生存所需下限2mg/L以下,鱼类在短时间内缺氧而死亡;当含沙量低于60kg/m3时,根据现场调查结果及相关人员经验判断水库下游河道内不会出现鱼类死亡漂移现象。水库排沙期间,下游河道水体的含沙量与溶解氧浓度具有较好的相关性,即河道水体的溶解氧浓度随着含沙量的增加而减少,可通过控制出库含沙量及其持续时间减轻对鱼类的影响。     

Biological consequences of agricultural and urban land-use along the Maumee River,a major tributary to the Laurentian Great Lakes watershed

Many riverine systems are impacted by a combination of agricultural and urban land use. In this study, we assessed the impacts of high intensity agriculture and urban land use in the Maumee River, the largest Great Lakes tributary, using sunfish (Lepomis spp.). The land use gradient from agricultural headwaters to densely urban areas was hypothesized to be paralleled by a shift in the chemical signature and biological effects. We caged hatchery-reared sunfish at field sites and collected concurrently resident sunfish. We analyzed fish for alterations in morphological indices, hematological characteristics, and anatomical development. Water, sediment, and fish tissues were analyzed for pesticides, pharmaceuticals, and personal care products. Chemicals were detected in all samples, and no clear agricultural/urban distinction in water chemistry was apparent. We detected forty-three chemicals (19% of analyzed) in at least half of the water samples, and 101 chemicals (44%) in at least one water sample. The pesticides desethylatrazine (100% of samples) and heptachlor epoxide (89%), and pharmaceuticals iopamidol (100%) and sulfamethoxazole (89%) were frequently detected. Resident sunfish were more sensitive than caged sunfish, and both experienced elevated stress responses at urban sites. Declining biological indices suggest contaminant-related impairments which may have altered resource allocation and could have contributed to decreased sexual maturity. Agricultural, and especially urban, contaminants entering aquatic ecosystems as non-point sources affect sunfish biology through acute and chronic exposure. Natural resource managers are advised to broadly assess stressors prior to investing into stream restoration efforts.     

Estimation of the Uptake of Organochlorines by the Mayfly Hexagenia limbata (Ephemeroptera: Ephemeridae)

Uptake rate coefficients (k_s) and biota-sediment- accumulation-factors (BSAFs) for 17 hydrophobic chemicals with octanol-water partition coefficients (log K_ow) ranging from 5.4 to 7.4 were determined for mayfly nymphs (Hexagenia limbata) exposed to contaminated sediments collected from the Detroit River. Nymphs obtained 95% of steady state conditions within a 32 day exposure period for all chemicals of study. Using two different exposure strategies, estimates of uptake rate coefficients ranged from 0.27 to 11.38 g(sediment)·g(lipid)^−l·h⁻¹ and became independent of K_owfor chemicals of log K_ow > 5.9. Biota Sediment Accumulation Factors ranged from 1.2 to 9.4, and followed similar trends as observed for k_s estimates. The results support the conclusion that bioaccumulation occurred as a result of ingestion of contaminant sorbed to sediment organic carbon, and that sediment was the primary chemical exposure route for hydrophobic organic chemicals with log K_ow > 5.9.     

基于IPSO-BP神经网络的高含沙水体对鱼类影响预测方法

水库进行水力排沙时，高含沙水流过程可能会对鱼类等水生动物产生负面影响，其量化评估方法研究较为薄弱。为了预测和评估水库排沙过程对下游鱼类的影响，本文利用黄河花斑裸鲤和鲤鱼在高含沙水体中生存特性研究的实验数据，综合考虑含沙量和粒径、溶解氧、暴露时间、水温等因子对鱼类生存的影响，建立了基于IPSO-BP神经网络的高含沙水体对鱼类致死影响预测方法，对目标鱼类死亡率的预测误差小于6%。本文使用了与BP神经网络紧密耦合并引入动态参数和变异扰动的IPSO算法，较BP和PSO-BP神经网络预测能力更佳，相比国内外已有的Stress Index(SI)、Severity of Ill Effect (SEV)和多元拟合方法预测精度得到显著提升。分析表明，本文提出的预测方法能够考虑高含沙水体中鱼类生存受多环境因子联合制约，且多因子之间存在复杂关联的情况，可为评估高含沙水流过程对水生态的影响提供新的方法。     

Acute impacts of reservoir sediment flushing on fishes in the Yellow River

Dam sediment flushing can reduce reservoir sedimentation and deliver sediments to the downstream rivers. However, deceased fishes are often found in the Yellow River during the period of reservoir sediment flushing. To study the acute impacts of flushing and quantify threshold conditions for fish protection, field surveys and laboratory experiments were carried out during periods of sediment flushing. Field surveys in 2010 showed that dissolved oxygen (DO) decreased rapidly with the increase in suspended sediment concentration (SSC) and that deceased fishes involved 10 species. With the model of the severity of ill effects, the sediment flushing in 2010 was estimated to cause fish mortality of 0–20%. To study the lethal effect on fishes under controlled SSC conditions, laboratory experiments were performed with carp (Cyprinus carpio) exposed in water containing different SSCs. It is concluded that the high sediment concentration (average value of 90788 mg/l), fine particles (grain size < 0.075 mm), a long flushing duration (>2 days), and DO reduction (<2 mg/l) contribute to the deaths of fishes during the flushing period in 2010. To decrease lethal effects, the upper limits of SSC and duration are recommended as the peak SSC value of 55 000 mg/l and average value of 32 000 mg/l for the entire flushing period for flushing operations. The measures of SSC control and refuge construction are suggested for eco-friendly management.     

水库排沙对下游河流鱼类影响研究进展

水库排沙对减轻水库淤积、延长水库寿命和恢复河流泥沙连续性等方面有着重要意义,但是水库进行水力排沙时水库下游河流水体的物理和化学性质的变化可能对鱼类等水生生物产生不利影响,严重时出现死鱼现象.国内外水库排沙时期下游河道含沙量及其颗粒级配、溶解氧浓度、污染物等水质变化对鱼类影响研究表明,微颗粒泥沙淤堵鱼鳃影响其摄入氧气功能和水体溶解氧下降是影响鱼类的两个主要因素,且含沙量及其持续时间、颗粒级配等对鱼类影响机理不同.最后展望了我国今后水库排沙对下游河流鱼类研究内容.     

The history and future of Lake Champlain's fishes and fisheries

In the last two centuries, physical, chemical, and biological alterations of Lake Champlain have resulted in the loss of two species, addition of 15 fish species, and listing of 16 species as endangered, threatened or of special concern. The lake currently supports 72 native fish species; lake trout (Salvelinus namaycush) and Atlantic salmon (Salmo salar) were extirpated by 1900, American eel (Anguilla rostrata) and lake sturgeon (Acipenser fulvescens) populations are extremely low, and walleye (Sander vitreum) are declining. Dams on several rivers, and ten causeways constructed in the mid 1800s to early 1900s, cut off access to critical spawning areas and may have limited fish movements. Siltation and sediment loading from agricultural activity and urban growth have degraded substrates and led to noxious algal blooms in some bays. A commercial fishery targeting spawning grounds of lake whitefish (Coregonus clupeaformis), lake trout, and walleye probably reduced numbers of these species prior to its closure in 1912. Non-native species introductions have had ecosystem-wide impacts. Sea lamprey (Petromyzon marinus) populations were very high prior to successful control, possibly as a consequence of ecological imbalance and habitat changes. A paucity of historic survey data or accurate species accounts limits our understanding of the causes of current fish population trends and status; in particular, the effects of habitat fragmentation within the lake and between the lake and its watershed are poorly understood. Holistic, ecosystem management, including pollution reduction and examination of habitat impacts, is necessary to restore the general structure of native biological assemblages.     

Environmental exposure of freshwater mussels to contaminants of emerging concern: Implications for species conservation

Contaminants of emerging concern (CECs) are prevalent in aquatic landscapes and may be a factor in population declines of aquatic and terrestrial fauna. Yet, there are limited data to assess the impacts of CECs to species. Understanding CEC impacts is particularly important for imperiled freshwater mussels which provide valuable ecosystem services. CEC exposure of freshwater mussels was characterized by evaluating sites with and without the federally endangered mussel (Villosa fabalis) in three subwatersheds of the Maumee River, Ohio, USA, a tributary of the Great Lakes Basin. Analyses of water, sediment, and tissue concentrations of two common mussels (Eurynia dilatata and Lampsilis cardium) indicated different CEC exposures across all 6 sites. Distinct CEC signatures were found across the three media types suggesting as mussels interact with water and sediment they may be experiencing different exposure concentrations and mixtures of CECs at different life stages. Of the 83 CECs which were detected, agricultural CECs dominated sediments, pharmaceuticals were common in tissues and water, and 16 of the 83 CECs were found co-occurring in mussel tissue, water, and sediment. There were no species differences in the CEC signatures indicating all mussels, including species of concern, may be experiencing similar exposure. Comparisons to known CEC standards indicate some exceedances in the Maumee watershed including locations of federally listed mussel species. This study provides evidence of the complexity of CEC mixes in a Great Lakes watershed and the need to understand how CECs impact declining aquatic fauna.     

Distribution and Bioaccumulation of Chlorinated Diphenyl Ethers in a Contaminated Embayment of Lake Ontario

Polychlorinated diphenyl ethers (PCDEs) are halogenated aromatic hydrocarbons that have structural similarities to polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans. PCDEs have been detected in piscivorus fish, fish eating birds and humans, but little is known about the transfer of these compounds through aquatic ecosystems. At sampling stations in the contaminated area of Whitby Harbour on the north shore of Lake Ontario, mean concentrations of total PCDE congeners in sediment were between 622 and 1,929 ng/g dry weight. Analysis of semipermeable membrane devices (SPMDs) deployed at several stations around the harbor indicated that PCDEs were distributed homogeneously in the water. Mean total PCDE concentrations in biota were as high as 672 ng/g wet weight (105 μg/g lipid) in white sucker (Catostomus commersoni) and 791 ng/g wet weight (55 μg/g lipid) in brown bullheads (Ameiurus nebulosus). The patterns of 45 PCDE congener analytes differed among the SPMDs, sediment, and biota, but between invertebrates and fish the congener patterns were relatively homogeneous. Bioamagnification factors (BMFs) calculated for total PCDEs in a simple benthic food chain (oligochaetes to white suckers) and a simple pelagic food chain (plankton to pumpkinseed) indicated that there was biomagnification, with BMFs < 50 on a lipid-normalized basis and BMFs < 5 on a wet weight basis. For individual PCDE congeners, there was a slight trend to increasing BMFs with increasing chlorine substitution.     

Benthic Bioaccumulation and Bioavailability of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans from Surficial Lake Ontario Sediments

The benthic bioavailability of surface sediment-associated polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) was quantified and assessed in Lake Ontario. Bottom sediments were collected from three areas along the Lake Ontario southern shoreline near Olcott, Rochester, and Oswego, New York. The sediment samples were subjected to 28-day, PCDD/F bioaccumulation experiments using the aquatic oligochaete Lumbriculus variegatus. Empirical data including only detectable PCDD/F tissue residues were used to quantify the benthic bioavailability of 11 PCDD/F congeners through the calculation of biota-sediment accumulation factors (BSAFs). BSAFs calculated for at least two lake areas were combined as Lake Ontario BSAFs for those specific congeners. Variability of the BSAFs was estimated by propagated error (PE) terms. Mean Lake Ontario BSAFs (±PE) ranged from 0.04±0.02 for octachlorodibenzofuran (OCDF) to 2.42±1.32 for 1,2,3,6,7,8-hexachlorodibenzofuran (HxCDF). Tetrachlorodibenzo-p-dioxin (TCDD) and 1,2,3,4,7,8-HxCDF, shown to be among the highest toxic equivalencies (TEQs) in lake sediments, yielded BSAFs of 0.51±0.18 and 0.22±0.12, respectively. Statistical comparison of the TCDD BSAFs showed no significant differences among the lake areas. The benthic bioavailability of TCDD appeared lower than the results of other investigators. While hydrophobicity and degree of chlorination play some role, other factors, such as steric properties, and composition of organic carbon and matter, may have had a greater influence on the benthic bioavailability of PCDD/F congeners. Comparisons of these benthic BSAFs to fish BSAFs suggest that the bioaccumulation of PCDD/F congeners by fish is more related to water solubility and degree of chlorination than to sediment concentration.     

Culturally adapted mobile technology improves environmental health literacy in Laurentian,Great Lakes Native Americans (Anishinaabeg)

The presence of persistent bioaccumulative toxics (PBT) in aquatic food chains complicates decision processes of people with a strong culture of fish consumption. This environmental contamination is especially problematic for Native American populations in the Laurentian Great Lakes region (Anishinaabeg). Pursuing the growing discipline of environmental health literacy (EHL) may help reduce toxic exposures, support healthy decision-making, and combat health deficits. Our goals for this research were first to improve environmental health literacy using novel technologies and second to help define environmental health literacy metrics that can be tracked over time, especially regarding culturally-contextualized health interests. We recently reported that a mobile app (Gigiigoo'inaan App) presenting personalized, culturally-contextualized fish consumption advice may improve EHL for the Anishinaabeg. Gigiigoo'inaan App safely supports desired fish consumption rates by putting local data into the hands of the Anishinaabeg. We conducted a pre-test post-test evaluation with 103 Aninishinaabe adults. Participants estimated their current fish meal consumption over a hypothetical month before exposure to the software and then planned their future consumption of fish meals in a month after using the mobile app. Significantly more monthly traditional fish meals on average (Median: 4 vs 2, p = 0.0005) were selected when using the app versus pre-exposure to the app. Significantly more traditional grams of fish were also selected during use of the app relative to the pretest (Median: 680.39 g vs 453.59 g, p = 0.0007). These increases were accompanied by widespread (97%) adherence to conventional advice that minimizes PBT exposure health effects (ATSDR minimum risk levels).     

Dynamics of PCBs in the Food Web of Lake Winnipeg

The bioaccumulation of polychlorinated biphenyls (PCBs) is examined in the food web of Lake Winnipeg using measured contaminant concentrations, stable isotopes of nitrogen, and a food web model. Measured concentrations of the sum of 103 PCB congeners are higher in south basin water, sediment, and biota compared with the north. The trophic positions of the top predators as well as the extent of biomagnification of PCBs per unit trophic level do not differ significantly between the north and the south basins. We therefore conclude that the higher PCB concentrations in the south basin are due primarily to higher PCB loadings via riverine sources to the south rather than food web processes. In contrast, the data from the north basin suggest lower total loadings of which a higher fraction is from atmospheric deposition. We find that rainbow smelt (Osmerus mordax) are not associated with elevated exposure of contaminants to top predators of the north basin. This surprising result is attributed to their reduced fitness in this relatively shallow and warm system, which may prevent them from feeding at an elevated trophic level compared with other forage fish. Finally, we hypothesize that high nutrient associated DOC in water decreases PCB bioavailability to lower trophic level organisms and hence the entire food web.     

The Impact of Changes in Water Level and Human Development on Forage Fish Assemblages in Great Lakes Coastal Marshes

Changes in water levels and development of shorelines are expected to negatively affect coastal marshes. The small-bodied fish assemblage was sampled in the inner marsh vegetation zone in five Les Cheneaux bays with differing levels of development. Observations were made from 1996 to 2004 during which time summer water levels varied from 177.2 m to 176.0 m (chart datum = 176.0 m). Each marsh was sampled for 10 consecutive days in July and August using gangs of five baited commercial minnow traps. Assemblage composition was assayed by species richness, the number of native minnow species, the percentage of selected tolerant fishes (bowfin, Amia calva, mudminnow, Umbra limi, common carp, Cyprinus carpio, and brown bullhead, Ameiurus nebulosus), and catch-per-unit-effort (CPUE). There were no consistent relationships between fish assemblage measures and year, water level, annual change in water level, exposure, and water temperature. Fish assemblage measures except CPUE were impacted by the density of building along the shoreline, a measure of development. Impervious surface area was < 4.5% and was not consistently related to fish assemblage measures.     

Trophic structure and mercury transfer in the subarctic fish community of Great Slave Lake,Northwest Territories,Canada

In recent decades, mercury concentrations have increased in fish of Great Slave Lake (GSL), a subarctic great lake in northern Canada with important recreational, subsistence, and commercial fisheries. This study characterized habitat use and trophic position of common fish species in GSL near the City of Yellowknife (Northwest Territories, Canada), measured mercury concentrations in water and in taxa from lower trophic levels of the food web, and examined trophic and biological influences on mercury concentrations within and among fish species. Northern pike (Exos lucius) and lake whitefish (Coregonus clupeformis) fed predominantly nearshore, cisco (Coregonus artedi) and longnose sucker (Catostomus catostomus) fed predominantly offshore, and burbot (Lota lota) fed roughly equally in both habitats. Habitat-specific feeding did not influence mercury bioaccumulation in fish, in contrast with published studies of smaller lakes. Water concentrations of total mercury and methylmercury were low and showed little spatial variation among sites or depths. Zooplankton (>200 μm) had similarly low methylmercury concentrations as littoral and profundal amphipods, suggesting little habitat-variation of mercury exposure near the base of the food web. Age, size, and trophic position were significant explanatory variables for muscle total mercury concentrations within populations of fish species. Among fish species, size and trophic position explained 80% of the variation in muscle total mercury concentrations. This study generated the most comprehensive dataset to date on mercury bioaccumulation in the food web of GSL, which will serve as a baseline for future studies of this great lake.     

Total and methyl mercury accumulation in 1994–1995 Lake Michigan lake trout and forage fish

As part of the Lake Michigan Mass Balance Project, total and methyl mercury were determined for lake trout (Salvelinus namaycush) and five forage fish species collected from Lake Michigan near Saugatuck, Michigan, and Port Washington, Sheboygan Reef, and Sturgeon Bay, Wisconsin, between 1994 and 1995. With a mean concentration of 179 ng/g wet wt., whole lake trout total mercury (Hg_T) concentrations ranged between 27.6 and 348 ng/g wet wt. For combined sites, 1–4 yrs, 5–6 yrs, 7–11 yrs, and 12–15 yrs lake trout mean Hg_T concentrations were 73.7, 130, 212, and 280 ng/g, respectively. Forage fish species alewife (Alosa pseudoharengus), bloater (Coregonus hoyi), slimy sculpin (Cottus cognatus), deepwater sculpin (Myoxocephalus thompsoni), and rainbow smelt (Osmerus mordax) had mean Hg_T concentrations of 63.8, 55.3, 36.7, 51.4, and 35.2 ng/g wet wt., respectively. With the exception of alewife, bloater, and slimy sculpin, all fish species contained approximately 100% methyl mercury (MeHg). Field bioaccumulation factors (BAF) were consistent with a Lake Michigan food chain that is more efficient at transferring MeHg to higher trophic levels than some inland lakes. This and other studies of lake trout from Lake Michigan document decreasing Hg_T concentrations in lake trout from 1971 to 1985 and constant or increasing concentrations between 1985 and 2000. These observations were supported by a similar trend in Lake Michigan Hg sediment fluxes. To our knowledge, this is the most intense two year study of mercury in fish for any Great Lake or other large fresh water system and is one of the most complete studies of mercury cycling in the Lake Michigan food chain.     

Temporal trends in near-shore sediment contaminant concentrations in the St. Clair River and potential long-term implications for fish tissue concentrations

Near-shore surface sediment of the St. Clair River (Ontario) extending along 9 km of waterfront downstream of local industries were contaminated with mercury (Hg), hexachlorobenzene, hexachlorobutadiene and octachlorostyrene based on data collected in 2006 and 2008. However, unlike Hg, concentrations of organic compounds were low at most stations suggesting improvements in sediment quality since 2001 (post sediment remediation projects). Concentrations of Hg were greater than Provincial Sediment Quality Guidelines and ranged as high as 41 μg/g in the surficial 0–5 cm sediment. Measured (2001–2004 data) and estimated (2006 data) concentrations of methyl Hg in invertebrates were greater than concentrations in invertebrates collected from upstream reference stations. Predicted methyl Hg concentrations in walleye using food chain multipliers, benthic invertebrate Hg tissue concentrations and current sediment concentrations exceeded human health consumption guidelines and were consistent with measured sport fish data supporting assumptions about Hg biomagnification. Historical data showed that for fish collected from the lower St. Clair River and Lake St. Clair, Hg concentrations have declined since 1978, but have remained stable since the mid 1980s, consistent with the sediment Hg data. The consistency in the sediment and fish datasets and the absence of a known significant local point source of Hg suggests that the sediment may be an important source of Hg to the St. Clair River food-chain.