A material balance study of polychlorinated biphenyls in Lake Michigan.

This paper integrates the known chemical and physical properties of polychlorinated biphenyls (PCB) derived in the laboratory with a mathematical model describing their behavior in Lake Michigan. The conclusion that emerges is that the observed levels of PCB both in Lake Michigan and the fish biomass are consistent with these laboratory measurements. In addition, it is concluded that it will take several years for this ecosystem to cleanse itself of the compounds even if no new input is made. The final sink for PCB is predicted to be degradation in the atmosphere, with some fraction being buried in the underlying sediments of the lake.     

Distribution of some trace metals in Lochnagar, a Scottish mountain lake ecosystem and its catchment

Anthropogenic trace metals enter the entire ecosystem of Lochnagar solely through atmospheric deposition. Trace metals, including Hg, have been monitored in atmospheric deposition and lake water, and measured in catchment vegetation, aquatic plants and zooplankton, revealing contamination levels in the ecosystem. Furthermore, 17 sediment cores were taken from different areas of the lake. Hg, Pb, Cd, Zn and Cu were analysed in all the cores, which show that the sediments have been heavily contaminated by these trace metals since the 1860s. The distribution of trace metals in the lake sediments was found to be heterogeneous, with concentrations in the surface sediments varying significantly: 110-250 ng/g, 100-360 microg/g, 39-180 microg/g, 0.3-1.9 microg/g and 8-25 microg/g for Hg, Pb, Zn, Cd and Cu, respectively. Trends in the concentration profiles for different trace metals in the same core are different, as are the trends of the profiles for the same metal in different cores. Hence, a single sediment core cannot represent the pollution history of the whole lake. As the soils and sediments contain a high proportion of plant debris and the debris has a high affinity for Hg, resulting in Hg enrichment. Hg was measured in plant debris (> 63 microm) separated from catchment soils and lake sediments. Plant debris may play an important role in storing and transferring Hg in this ecosystem.     

Distributions of total mercury and methylmercury in surface sediments and fishes in Lake Shihwa, Korea

The concentrations of total mercury (THg) and methylmercury (MeHg) in the sediments of Lake Shihwa, an artificial salt lake in Korea located near two large industrial complexes, were determined to investigate the state of Hg contamination in the lake sediments and the effect of local Hg source. THg and MeHg concentrations in the sediments, monitored for 2 years, ranged from 0.02 to 0.28 µg g^− 1 and ≤ 0.026 to 0.67 ng g^− 1, respectively. The overall distribution of Hg in lake sediments showed higher values near industrial complexes and in the central part of the lake. However, the correlations between Hg and environmental factors, such as organic material (OM) content, and acid volatile sulfide (AVS), were weak and did not clearly explain the variation in Hg distribution. The spatial distribution of sediment Hg and monthly precipitation data during the sampling period showed that the amount of runoff following rain events and water gate operation may be additional important factors regulating Hg level and distribution in lake sediments. The levels of THg in fish species in this lake ranged from 9.8 to 35 ng g^− 1, suggesting that the bioavailability of sediment Hg in the lake may be low. Although the THg concentrations in Lake Shihwa sediment were lower than those in other foreign study sites, they were higher than in neighboring coastal regions, and are constantly increasing. This result indicates that the nearby industrial complexes may be the major source of Hg found in the sediments of Lake Shihwa.     

Influence of intensive fishing on the partitioning of mercury and methylmercury in three lakes of Northern Québec

It has been demonstrated that intensive fishing, i.e., removing more than 25% of the fish biomass, can reduce mercury levels in predator fish in a lake. We test here the hypothesis that, by removing an important part of the fish biomass from a lake, a significant amount of methylmercury can be eliminated, therefore reducing the mercury available to the remaining biota, at least in the short term. A mass burden approach is used to evaluate the partitioning of total mercury and methylmercury in natural lake ecosystems. Three small natural lakes from the James Bay territory, in northern Québec, Canada, were selected for intensive fishing. Mercury (Hg) and methylmercury (MeHg) concentrations were evaluated for sediments, water column (dissolved fraction and suspended particulate matter), plankton, aquatic invertebrates, and fish. Biomasses were determined for fish, plankton, and aquatic invertebrates. Two case scenarios are presented using different mercury contributions from the sediment component (1 cm depth, and no sediment). Our results for the scenario including the sediment contribution show that lake sediments represent over 98% of the total mercury while the biotic components represent less than 0.1% of the same burden. For methylmercury, fish account for up to 5% of the burden, while sediments make up 84.6% to 93.1%. If we put aside the sediment contribution, the methylmercury in fish partitioning can represent up to 48%. As for invertebrates, they can account for up to 48% of the total MeHg burden. We do not observe any change in the partitionings or the quantities of Hg and MeHg before and after fishing in either of the two case scenarios even when we do not take into account dynamics of the ecosystems. This will be all the more the case when the dynamics of the system are included in the analyses. Therefore, biological parameters such as growth rates or fish diet must be considered.     

Application of potassium chloride to a Chernobyl-contaminated lake: modelling the dynamics of radiocaesium in an aquatic ecosystem and decontamination of fish

This study tests a whole-lake experiment to reduce the bioaccumulation of radiocaesium (137Cs) in fish in lakes contaminated by the Chernobyl accident. In many lakes in the Chernobyl contaminated areas, radiocaesium activity concentrations in fish are still significantly higher (up to 100 times in some species) than acceptable limits for human consumption. Estimates of the long-term rate of decline of 137Cs in fish in these regions, in the absence of countermeasures, show that radioactivity in fish in some lakes may remain above acceptable consumption limits for a further 50-100 years from the present date. In February 1998 we applied 15 t of potassium chloride to Lake Svyatoe, Kostiukovichy. The addition of potassium chloride fertilizer to the lake resulted in a decrease in activity concentration of 137Cs to approximately 40% of pre-countermeasure values in a number of different fish species. In contrast to Lake Svyatoe, 137Cs activity concentrations in fish from four control lakes showed no systematic decrease over the study period. Simplified models for transfers of 137Cs in lakes successfully 'blind' predicted the changes in 137Cs in water and fish resulting from this major alteration of the potassium concentration of the lake. The experiment represents the first test of a predictive model for the dynamics of radiocaesium in response to a major perturbation in potassium (its major competitor ion) in a whole lake ecosystem.     

A field studies and modeling approach to develop organochlorine pesticide and PCB total maximum daily load calculations: Case study for Echo Park Lake, Los Angeles, CA

Echo Park Lake is a small lake in Los Angeles, CA listed on the USA Clean Water Act Section 303(d) list of impaired water bodies for elevated levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in fish tissue. A lake water and sediment sampling program was completed to support the development of total maximum daily loads (TMDL) to address the lake impairment. The field data indicated quantifiable levels of OCPs and PCBs in the sediments, but lake water data were all below detection levels. The field sediment data obtained may explain the contaminant levels in fish tissue using appropriate sediment-water partitioning coefficients and bioaccumulation factors. A partition-equilibrium fugacity model of the whole lake system was used to interpret the field data and indicated that half of the total mass of the pollutants in the system are in the sediments and the other half is in soil; therefore, soil erosion could be a significant pollutant transport mode into the lake. Modeling also indicated that developing and quantifying the TMDL depends significantly on the analytical detection level for the pollutants in field samples and on the choice of octanol-water partitioning coefficient and bioaccumulation factors for the model.     

Strategic environmental management: time for a new approach

We present a comprehensive analysis of the sensitivity of mercury (Hg) human exposure to environmental variables using a multimedia model of the fate and transport of Hg in the environment. The results of the analysis show that the Hg dose is most sensitive to the lake pH, the burial rate of Hg adsorbed to sediments, and the chemical speciation of Hg emissions to the atmosphere. The lake pH has a strong non-linear effect on the methylation rate and bioaccumulation of Hg in fish. The burial of sediments is a major pathway for removing Hg from the lake cycling. The speciation of Hg emissions is important because Hg(II) is deposited much more rapidly than Hg(0). These results highlight the importance of key variables that should be investigated through well-designed field programs, so that we can minimize the overall uncertainties associated with the modeling of mercury fate and transport.     

A 1500-year record of lead, copper, arsenic, cadmium, zinc level in Antarctic seal hairs and sediments

To reconstruct the profiles of heavy metal levels in the South Ocean ecosystem of Antarctica, the concentrations of lead (Pb), copper (Cu), arsenic (As), cadmium (Cd), and zinc (Zn) in seal hairs and lake sediments spanning the past 1500 years from Fildes Peninsula of King George Island and in weathering lake sediments from Nelson Island of West Antarctica were determined. The lead contents in the seal hairs and the weathering sediments show a sharp increase since the late 1800s, very likely due to anthropogenic contamination from modern industries. After the 1980s, the Pb content in seal hairs dropped by one-third, apparently due to the reduced usage of leaded gasoline in the Southern Hemisphere. Copper arises mainly from the weathering process, and its level may be substantially affected by climatic conditions. The concentrations of Cd, As, and Zn do not show any clear temporal trends.     

Polycyclic aromatic hydrocarbons in fish from remote and high mountain lakes in Europe and Greenland

Polycyclic aromatic hydrocarbons (PAHs) were analysed in liver of fifty-seven individual trout distributed among seven high mountain lakes in Europe and one remote lake in Greenland. In all cases, very similar distributions were observed in which phenanthrene largely predominated and fluoranthene and pyrene were the second major compounds. These distributions were similar to those observed in the dissolved fraction of the waters studied in three of these lakes. The range of concentrations of PAH in fish liver show only a five-fold variation, which is considerably smaller than the range more than two orders of magnitude of sedimentary PAH concentrations of these lakes. No correlation between PAH content in sediments and fish liver has been found both at the level of total and individual compounds. However, lake site is the main statistically significant factor of variability between PAH concentrations in fish liver. Changes in fish species explain significant differences in liver content of some PAHs. Within lake, condition factor and liver concentration are inversely correlated. Female fish display lower average concentrations than male in all lakes but the differences are not statistically significant. No correspondence between fish age and PAH content has been observed.     

Mercury in Arctic char (Salvelinus alpinus) populations from Greenland

Mercury concentrations were determined in muscle tissue of lake resident and anadromous populations of Arctic char in Greenland. Mercury in lake sediment, and in soil and humus from the surrounding area were also determined in the main localities. Fish length and dry weight were shown to be important covariables, which have to be taken into account when comparing mercury levels between populations. Variations in fat content did not contribute further to the differing mercury concentrations. Mercury concentrations in lake sediments, humus from around the lakes and resident populations of Arctic char from west Greenland and south-west Greenland were higher than for populations from east Greenland and north-west Greenland. The mercury level in anadromous populations was found to be 10-15-fold lower than that found in lake resident populations, and similar to that found in marine fish species. Methyl mercury was determined in two of the populations investigated, and constituted 72-92% of the total mercury.     

五里湖富营养水体生态重建试验

为了改善五里湖水环境,从2002年起,展开对五里湖及其周边地区综合整治、西五里湖生态重建与示范工程。初步结果表明,西五里湖水质得到一定的改善,水体透明度也有所提高,尤其是示范工程区内透明度的平均值比湖区的高1.6倍。最好的水质出现在示范工程区内,与未进行生态恢复的东五里湖相比,水体中的TN、TP、Chl.a、NH4-N及NO2-N均有较大幅度降低,但CODMn、NO3-N、SD差异不大。湖滨生态景观有了较大改善,建立了具有生态景观效果的芦苇、狭叶香蒲、水菖蒲、水生类鸢尾及美人蕉等湖滨湿地近1.0万m2;在敞水区恢复了浮叶、沉水植物超过3.5万m2。通过生态重建实践,对浅水湖泊生态恢复提出了建议。     

Mercury concentrations in fish inhabiting two polluted lakes in Northern Canada

The concentrations of total mercury in the sediments, water and fish of Giauque Lake and Thompson Lake in northern Canada were determined during 1977 and 1978. Both lakes had formerly received mercury-laden industrial discharges, which were terminated in 1968 (Giauque Lake) and 1949 (Thompson Lake). In Giaque Lake, lake trout (Salvelinus namaycusy) contained an average of 3.79 mg kg⁻¹ in their muscle while the average concentrations in northern pike (Esox lucius) and round whitefish (Prosopium cylindraceum) were 1.75 and 1.22 mg kg⁻¹ respectively. About 7% of the lake's bottom contained mercury levels of > 500 μg kg⁻¹ (dry weight) but, in the water, concentrations were always below detectable limits (0.2 μg l⁻¹). In Thompson Lake, mercury levels in northern pike averaged 1.69 mg kg⁻¹, whereas in lake whitefish (Coregonus clupeaformis), the highest recorded value was 0.6 mg kg⁻¹. Although mercury was usually not detectable in the water column, there was heavy contamination of the sediments, with values reaching 1300 μg kg⁻¹. In addition, approximately 15% of the lake bottom contained mercury in excess of 500 μg kg⁻¹. Based on these data, it is concluded that: (1) northern pike are still accumulating mercury from exposed tailings which were deposited in Thompson Lake 30 years ago, and (2) contamination of only a small part of a lake may result in high levels in fish throughout the lake: this is probably due to the movement of fish from contaminated to noncontaminated areas.     

Source characterization using compound composition and stable carbon isotope ratio of PAHs in sediments from lakes, harbor, and shipping waterway

Molecular compositions and compound specific stable carbon isotope ratios of polycyclic aromatic hydrocarbons (PAH) isolated from sediments were used to characterize possible sources of contamination at an urban lake, a harbor, a shipping waterway, and a relatively undisturbed remote lake in the northwest United States. Total PAH concentrations in urban lake sediments ranged from 66.0 to 16,500 microg g(-1) dry wt. with an average of 2600 microg g(-1), which is approximately 50, 100, and 400 times higher on average than PAH in harbor (48 microg g(-1) on average), shipping waterway (26 microg g(-1)), and remote lake (7 microg g(-1)) sediments, respectively. The PAH distribution patterns, methyl phenanthrene/phenanthrene ratios, and a pyrogenic index at the sites suggest a pyrogenic origin for PAHs. Source characterization using principal component analysis and various molecular indices including C2-dibenzothiophenes/C2-phenanthrenes, C3-dibenzothiophenes/C3-phenanthrenes, and C2-chrysenes/C2-phenanthrenes ratios, was able to differentiate PAH deposited in sediments from the four sites. The uniqueness of the source of the sediment PAHs from urban lake was also illustrated by compound specific stable carbon isotope analysis. It was concluded that urban lake sediments are accumulating PAH from sources that are unique from contamination detected at nearby sites in the same watershed.     

Biotic condition assessment and the implication for lake fish conservation: a case study of Lake Qionghai, China

Conserving fish in lakes requires the systematic analysis and assessment of fish species. The issues, conservation needs and fish assemblage changes are described for Lake Qionghai (China). The annual fishery production (AFP) was analysed from 1949 to 2003, which indicated a high disturbance of the aquatic ecosystem in Lake Qionghai caused especially by fisheries. The continuous increase in AFP and the introduction of economically important fish species have changed the fish species structure and diversity of the lake. Only five of 20 native fish species remained extant in 2003. The alien species accounted for 83.58% of the total fish production in 2003. Scoring criteria for 10 indexes of biotic integrity (IBI metrics) were selected for Lake Qionghai. The overall IBI score decreased from 40 in the 1940s to 26 in the 1980s to 20 in 2003. Changes in biotic condition were mainly caused by the destruction of fish physical habitat, pollution, bycatch and the invasion of alien species. Based on the IBI analysis, an ecosystem approach was developed for fish conservation in Lake Qionghai, including conservation at the watershed scale, habitat improvement and restoration, rebuilding of aquatic ecosystems and adaptive ecosystem-based fishery management.     

Mutagenic activity of fish and sediments in the Sheep River, Alberta

Using the Ames Salmonella/mammalian microsome assay the mutagenic activity of fish and benthic sediments from a section of the Sheep River. Alberta receiving a chlorinated sewage effluent were investigated. The benthic sediments gave no indication of increased mutagenic activity, however fish collected from the chlorinated sewage plume showed a significant increase in mutagenic activity. The results are discussed with respect to the effects of a chlorinated sewage effluent on the lotic ecosystem in this section of the river.     

Silver contamination on abiotic and biotic compartments of Nahuel Huapi National Park lakes, Patagonia, Argentina

The Ag contents of abiotic and biotic compartments of different lakes of Nahuel Huapi National Park, Patagonia, Argentina were analyzed. The water bodies studied were lakes Nahuel Huapi, Moreno, Escondido, Espejo Chico and Traful, the latter chosen as a reference lake. The Ag concentration profiles of short sediment cores, dated by (210)Pb and (137)Cs techniques, were analyzed, as well as suspended load collected from three sites of lake Nahuel Huapi. The biota studied were the native mussel Diplodon chilensis (digestive gland and total soft tissues pooled samples) and five species of fish, two native and three introduced (liver and muscle pooled samples). Ag contents were determined by Instrumental Neutron Activation Analysis (INAA). The upper layers of the sediment cores sampled in lake Nahuel Huapi were enriched in Ag contents compared to deep layers in accumulation periods corresponding to the second half of the 20th century, but this enrichment was neither observed in the reference lake Traful, nor in lakes Espejo Chico and Escondido. Ag was enriched over background level (0.1 microg g(-1)) also in suspended load collected in lake Nahuel Huapi. Ag fluxes to sediments were computed for suspended load and enriched sediment core layers. Highest Ag fluxes, from 350 to 470 microg m(-2) year(-1), were measured in Nahuel Huapi near the site where the liquid effluents of the Bariloche city sewage treatment plant are released to the lake. The spatial distribution of the other Ag fluxes suggests that this is the main source of Ag to lake Nahuel Huapi and lateral transport occurs within the water body. Ag concentrations on biota samples were consistent with these conclusions. Mussels collected in lake Nahuel Huapi showed higher Ag concentrations than in the other lakes, especially when compared to lake Traful. Ag contents in mussels were strongly associated with sediment intake, but enriched probably due to sediment grain size sorting during the intake processes. Evidence of food chain biomagnification of Ag in fish liver was observed. Ag contents in fish liver were higher at lake Nahuel Huapi even considering the high intra-specific variability, with highest values ranging from 10 to 29 microg g(-1) dry weight for brown trout and rainbow trout.     

Climate induced thermocline change has an effect on the methyl mercury cycle in small boreal lakes

We conducted a whole-lake experiment by manipulating the stratification pattern (thermocline depth) of a small polyhumic, boreal lake (Halsjärvi) in southern Finland and studying the impacts on lake mercury chemistry. The experimental lake was compared to a nearby reference site (Valkea-Kotinen Lake). During the first phase of the experiment the thermocline of Halsjärvi was lowered in order to simulate the estimated increase in wind speed and in total lake heat content (high-change climate scenario). The rate of methyl mercury (MeHg) production during summer stagnation (May-August) was calculated from water profiles before the treatment (2004), during treatment (2005, 2006) and after treatment (2007). We also calculated fluxes of MeHg from the epilimnion and from the hypolimnion to the sediments using sediment traps. Experimental mixing with a submerged propeller caused a 1.5-2 m deepening of the thermocline and oxycline. Methyl mercury production occurred mostly in the oxygen free layers in both lakes. In the experimental lake there was no net increase in MeHg during the experiment and following year; whereas the reference lake showed net production for all years. We conclude that the new exposed epilimnetic sediments caused by a lowering of the thermocline were a major sink for MeHg in the epilimnion. The results demonstrate that in-lake MeHg production can be manipulated in small lakes with anoxic hypolimnia during summer. The climate change induced changes in small boreal lakes most probably affect methyl mercury production and depend on the lake characteristics and stratification pattern. The results support the hypothesis that possible oxygen related changes caused by climate change are more important than possible temperature changes in small polyhumic lakes with regularly occurring oxygen deficiency in the hypolimnion.     

On the relationship between lake trophic level and lake sediments

The purpose of this work has been to study the relationship between lake type, as expressed by various trophic characteristics, and sediment type, as expressed by determinations of simple chemical data on nitrogen, phosphorus, carbon and loss on ignition. The study is based on two sets of data. The first one emanates from 71 lakes for which information is available from published sources on trophic level and N-content and organic content (loss on ignition) from surficial sediments. More detailed information has been obtained from 12 Swedish lakes/basins on the following water indicators of trophic level: transparency, chlorophyll-a, total-N, total-P, organic-N, inorganic-N. The sediment data from these 12 lakes include: mean values and characteristic values for organic content (loss on ignition, IG) C-, N- and P-contents from surficial sediments. A BPN-value (bioproduction number) is defined by the slope coefficient of the regression line between N-content and IG-content of surficial sediments (0–1 cm). It has been shown that the BPN-value provides most accurate information about lake trophic level on the scale from oligotrophy to eutrophy, provided that more than 50% of the lake area has lower loss on ignition than 20% (per dry substance). The BPN-value cannot be used as an indicator of trophic level if the IG-content is predominantly higher than 30% in a lake. In the latter case the ratio IG/N can be used as a means to differentiate lake humic level. The BPN-value, which is determined from sediment samples providing an even spread throughout the lake surface, yields lake typical information, whereas C/N ratios yield site specific information. A key diagrammatic interpretation between lake trophic type and lake sediments has been presented.     

Selenium and trace element mobility affected by periodic displacement of stratification in the Great Salt Lake, Utah

The Great Salt Lake (GSL) is a unique ecosystem in which trace element activity cannot be characterized by standard geochemical parameters due to the high salinity. Movement of selenium and other trace elements present in the lake bed sediments of GSL may occur due to periodic stratification displacement events or lake bed exposure. The water column of GSL is complicated by the presence of a chemocline persistent over annual to decadal time scales. The water below the chemocline is referred to as the deep brine layer (DBL), has a high salinity (16.5 to 22.9%) and is anoxic. The upper brine layer (UBL) resides above the chemocline, has lower salinity (12.6 to 14.7%) and is oxic. Displacement of the DBL may involve trace element movement within the water column due to changes in redox potential. Evidence of stratification displacement in the water column has been observed at two fixed stations on the lake by monitoring vertical water temperature profiles with horizontal and vertical velocity profiles. Stratification displacement events occur over periods of 12 to 24 h and are associated with strong wind events that can produce seiches within the water column. In addition to displacement events, the DBL shrinks and expands in response to changes in the lake surface area over a period of months. Laboratory tests simulating the observed sediment re-suspension were conducted over daily, weekly and monthly time scales to understand the effect of placing anoxic bottom sediments in contact with oxic water, and the associated effect of trace element desorption and (or) dissolution. Results from the laboratory simulations indicate that a small percentage (1%) of selenium associated with anoxic bottom sediments is periodically solubilized into the UBL where it potentially can be incorporated into the biota utilizing the oxic part of GSL.