The influence of trophic level as measured by δ15N on mercury concentrations in freshwater organisms

The relationship between mercury (Hg) concentrations in freshwater biota and trophic position, as defined by stable nitrogen isotope ratios (δ¹⁵N), was examined in 6 lakes in northwestern Ontario. The heavier isotope of nitrogen (¹⁵N) increases an average of 3 parts per thousand (‰) from prey to predator and is used as a measure of an organism's trophic position. Dorsal muscle from lake trout, burbot, walleye, northern pike, white sucker, lake cisco, lake whitefish, and yellow perch was analyzed for Hg and δ¹⁵N using flameless atomic absorption and mass spectrometry respectively. Within each lake, log Hg was significantly related to δ¹⁵N (r ² ranged from 0.47 to 0.91,P<0.01). For four species, yellow perch, northern pike, lake cisco, and lake trout, log Hg was positively related to δ¹⁵N (r ² ranged from 0.37 to 0.47,P≤0.09) across all lakes. We also used δ¹⁵N measurements (assuming a 3‰ shift between an organism and its diet) and the developed within-lake regression equations to calculate a prey Hg for each individual fish. These food Hg values were then used to predict predator Hg using Norstromet al's bioenergetics model. Predicted results were strongly correlated to measured Hg concentrations (r=0.91,P<0.001), indicating that δ¹⁵N has potential to be used in modeling.     

Low Success Rate in Re-Establishing European Perch in Some Highly Acidified Lakes in Southernmost Norway

In order to test whether major reductions in acid inputs had improved water quality sufficiently for fish populations to recover, we stocked wild European perch (Perca fluviatilis) in three highly acidified lakes that had previously supported this species, and in one limed lake. The fish, which were introduced from a local lake (donor lake), generally ranged from 12 to 16 cm in total length, and were stocked at densities of 117–177 fish ha^?1. The untreated lakes were highly acid, with minimum pH values and maximum inorganic aluminium concentrations (Al_i) during the spring of 4.6–4.7 and 118–151 µg L^?1 respectively. In the limed lake, the corresponding values for pH and Al_i ranged between 5.8 and 6.6 and 5 and 19 µg L^?1 respectively. Gill-netting in two subsequent years after the introduction yielded only a few recruits (0+) and one adult in one of the three acidified lakes in one year only. However, stocked perch reproduced successfully in both years in the limed lake. There was a significant linear relationship between the catches (CPUE) of juvenile perch (age 0+) in the different lakes in the autumn and the water quality in May (time of hatching), both in terms of Al_i (r ²=0.934, P<0.05) and pH (r ²=0.939, P<0.05). Our data suggest unsuccessful recruitment in waters of pH <5.1 and Al_i>60 µg L^?1.     

Concentrations of trace elements in yellow perch (Perca flavescens) from six acidic lakes

Yellow perch (Perca flavescens) were collected from six small acidic lakes in northwestern New Jersey. Analyses of muscle tissue identified a pattern of increased concentrations of Hg in fish from the most acidic lakes; levels of Cd and Pb were greatly elevated in livers of specimens from two of the most acidic lakes. At one site, Sunfish Pond, positive correlations between fish size and Hg levels in muscle and Cd concentrations in livers were detected. In only one case did Hg concentrations in muscle tissue exceed the U.S. FDA action level of 1 μg g^?1 (wet wt).     

Changes in the fish community of a limed lake near sudbury,Ontario: Effects of chemical neutralization or reduced atmospheric deposition of acids?

Nelson Lake, a moderately acidic (pH 5.7), metal-contaminated (Cu 22 μg L^?1; Zn 18 ug L^?1) lake, 28 km from the smelters at Sudbury, had a degraded fish community in the early 1970's, with lake trout (Salvelinus namaycush) scarce, smallmouth bass (Micropterus dolomieui) extinct, and the littoral zone dominated by the acid-tolerant yellow perch (Perca flavescens). Liming of the lake in 1975–76 increased pH to 6.4, and decreased metal concentrations. Chemical conditions have remained relatively stable in the 10 yr following base addition. Initially, it appeared that neutralization produced dramatic changes in the resident fish community. Yellow perch abundance declined rapidly after neutralization, lake trout abundance increased to the extent that 3.26 kg ha^?1 were caught in the winter of 1980, and reintroduced smallmouth bass reproduced and established a large population. However, these changes in the fish community can not be directly attributed to liming, as water quality and the sport fisheries of an unlimed nearby lake also improved. Reduced emissions from Sudbury smelters were responsible for improvements in the untreated lake. Recovery of the lake trout population in Nelson Lake appears to have begun prior to liming. Of the lake trout sampled during the 1980 winter fishery, 65.8% were present prior to the chemical treatment. Predation by lake trout was the likely cause of the perch decline. Our results suggest that chemical conditions producing population level responses in fish have abrupt thresholds and that neutralization of lakes above these thresholds may not produce distinguishable effects.     

Impact of acidification on the methylmercury cycle of remote seepage lakes

Concentrations of monomethylmercury [CH₃Hg] were measured in the water and seston of five nearly pristine Wisconsin lakes, which span a range of pH from about 4.6 to 7.2. Previous studies had established a clear inverse relationship between [CH₃Hg] in fish and the pH of lakes in this region. Here, we examined the pH dependency of [CH₃Hg] in lake water and explored the partitioning of CH₃Hg between water, seston, and fish as a function of pH. Results indicate that [CH₃Hg] in lake water tends to increase as pH decreases, but that seasonal and spatial variability of [CH₃Hg] in individual lakes confounds a simple analysis of the relationship. The partitioning of CH₃Hg was related only weakly, if at all, to pH. Average partitioning coefficients (log k_d=log (C_p/C_w)) were higher for yearling yellow perch (6.0 to 6.5) than for seston (5.5 to 6.0) but did not vary significantly between lakes. This suggests that acidification has a stronger effect on the supply of CH₃Hg to the ecosystem than on specific rates of uptake by the biota.     

Treatment of mercury contaminated fish by selenium addition

Treatment of Hg contaminated fish by addition of Se (the Boliden SRM-method) has been shown to be an effective mean to reduce the Hg concentration of pike and perch. The fullscale tests in eleven lakes in Sweden have confirmed the earlier results in lake Öltertjärn in Sweden. The 1 yr old perch in the treated lakes shows a reduction in the mean Hg concentration. The Hg concentration in tissue varied between 0.04 and 0.29 mg kg in the different lakes before treatment. After treatment the Hg concentration decreased to 0.02 to 0.07 mg kg^?1. The reduction in perch was as much as 60% for the three lakes with lower background concentration in pike (less than 0.7 mg kg^?1) and as high as 85% for eight lakes with higher concentrations. In pike with Hg concentration at or above 1 mg kg^?1it was reduced by 22% after only I yr and by 28% after 2 yr of treatment. Experience gained in these tests verifies the importance of adjusting the dose and addition period to the lake. Good circulation in the lake is essential during addition.     

Trace element concentrations in fish from three Adirondack lakes with different pH values

Concentrations of 29 elements were detected in the axial muscle, and 44 elements were detected in the gut contents of white suckers (Catostomus commersoni) and yellow perch (Perca favescens) from three lakes located in the New York State Adirondack Preserve. The study lakes were acidic Darts Lake, variable pH Lake Rondaxe, and circumneutral Moss Lake. For the majority of the elements, there were no clear differences in the muscle concentrations among fish inhabiting the three types of lakes. Two notable exceptions were Hg and Pb. With some exceptions, the highest muscle tissue Pb concentrations were found in fish from the acidic lake. For both species, the Hg was higher in the muscle than in the gut regardless of lake acidity. Other elements potentially toxic to humans (As, Cd, Ga, Pb, Se, and TI) were not accumulated in the muscle relative to the gut.     

Trace element accumulation in the tissues of fish from lakes with different pH values

Two species of fish, omnivorous Catostomus commersoni (white suckers) and carnivorous Perca flavescens (yellow perch) were collected from three natural lakes with different pH ranges (circumneutral, pH 6.5 to 6.8; variable, pH 5.8 to 6.7; and acidic, pH 4.9 to 5.4). The lakes are located in the North Branch of the Big Moose River drainage system in the New York State Adirondack Park Preserve. Concentrations of potentially toxic elements (Al, Cd, Cu, Ph, and Se) were measured by electrothermal atomic absorption spectrophotometry in water, sediment and fish (bone, gill, kidney, liver and muscle) from each lake. The results showed that concentrations of Pb and Cd were significantly higher (P < 0.05) in some of the tissues of the fish collected from the acidic lake. Also, the yellow perch from the acidic take had significantly higher (P<0.05) Se concentrations in their muscle and livers than fish from the other lakes. The concentrations of Al were elevated in the gill tissues of both fish species from the acidic lake relative to fish from the other lakes. Possible mechanisms contributing to these differences in tissue concentration are discussed.     

Distribution of total mercury in coastal sediments from Jade Bay and its catchment, Lower Saxony, Germany

Purpose

Sediment cores provide a reliable record of mercury (Hg) contamination and can be used to study long-term Hg pollution and relevant environmental change. In the last hundred years, there were several events which may have contributed to the accumulation of Hg in Jade Bay and its catchment. This work was undertaken to assess the record in total Hg (THg) content in sediments of cores from Jade Bay and its catchment.

Materials and methods

A 5-m sediment core from Jade Bay, Lower Saxonian Wadden Sea, southern North Sea and a 12-m core from its catchment area (Wangerland, coastal zone of the Jade Bay) were used to study Hg contents in sediments. Total Hg, grain size distribution, aluminium (Al) and total organic carbon (TOC) were analysed on subsamples of both sediment cores. Total Hg was determined by oxygen combustion-gold amalgamation using DMA-80.

Results and discussion

As THg contents of the Jade Bay core were positively correlated to the sum of TOC and Al contents (r ²?=?0.86, p?<?0.001), the Hg data were interpreted using a regional normalisation function with the sum of Al and TOC as the normalisation parameters. Total Hg contents of the Wangerland core were correlated better to Al contents (r ²?=?0.70, p?<?0.001) than to the sum of TOC and Al contents (r ²?=?0.63, p?<?0.05). Therefore, Hg contents in sediments of the Wangerland core were normalised to Al contents. Comparison between enrichment factors and the background range of the sediment cores suggested that Jade Bay was contaminated about 50 years ago, and that Wangerland, or the catchment area of Jade Bay, was contaminated about 300 years ago, if no diagenetic remobilization occurred.

Conclusions

Total Hg contents of both cores were low and of no concern to the aquatic environment of Jade Bay. The Hg record was in good agreement with the history of industrial development in the region; thus, Hg deposition could have occurred through atmospheric input, ammunition residues of the Second World War and volcanic emanations, as well as through diagenetic remobilization.     

Time resolution of mercury dose and lake sensitivity related to mercury content in fish

This work treats data from 75 small, mainly oligotrophic Swedish forest lakes. The aim is to study and evaluate the temporal variation of different Hg-dose and lake sensitivity parameters vs. Hg in 1-kg pike and small perch (<10 g). The lakes were treated with different remedies (such as lake liming) during 1987 in order to reduce Hg-levels in fish. Lake water chemistry has a large seasonal variation but the yearly means is clearly affected by the treatments (mean alkalinity is increased from 0.05 to 0.19 mcq^*L⁻¹). There is a marked change of Hg in perch 2 yr after treatment; the median decrease is 33%, a further time delay of about 2 yr is suggested for Hg in pike. Among the dose parameters, Hg in material from sediment traps and in water the fraction RIHg seem to be affected by the remedies with an accentuated decrease during 1988, while a slight increase of total-Hg (THg) in water can be observed. A regression model where the Hg content in perch (Hg-pe) is predicted by Hg-dose, pH and lake water retention time is presented (r²=0.71, n=22) as an example of the importance of using time compatible data with respect to the effect parameter (Hg-pe).     

Mercury in fish muscle in acidified and limed lakes

The concentration of Hg in muscle was monitored during 10 to 12 years in different size and age groups of pike (Esox lucius) and perch (Perca fluviatilis). The study was performed in one reference and five lime treated lakes. Before liming, the highest levels of Hg in fish were measured in a lake with an annual mean pH just above 5.0. Lower levels were obtained both in lakes which were more acidified and in those which were less acidified. After the start of liming, the fastest and largest changes were obtained in the lakes which were moderately acid before liming (mean pH 5.4–5.8). In small perch, the Hg-concentration was markedly reduced in two years and showed an 80 % decrease in ten years. A slower response was registered in the lakes originally having about 0.5 units lower pH. In the most acidified lake (pH 4.9) the concentrations even increased the first years after liming, but decreased again later on. The possible mechanisms involved are discussed.     

The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes

A number of recent studies have documented elevated concentrations of mercury (Hg) in fish caught in remote lakes and a pattern of increased concentrations of Hg in fish tissue with decreasing water column pH. Because of the potential linkage between fish Hg and surface water acidification, factors regulating water column concentrations and bioavailability of Hg were investigated in Adirondack lakes through a field study and application of the Mercury Cycling Model (MCM). Concentrations of total Hg and total MeHg were highly variable, with concentrations of total MeHg about 10% of total Hg in lakes which did not show anoxic conditions. In lakes exhibiting anoxic conditions in the hypolimnion during summer stratification, concentrations of total MeHg were elevated. Concentrations of total Hg and total MeHg increased with decreasing pH in remote Adirondack lakes. However, more importantly, concentrations of total Hg and total MeHg increased with increasing concentrations of dissolved organic carbon (DOC) and percent near-shore wetlands in the drainage basin. Mercury concentrations in muscle tissue of yellow perch from Adirondack lakes were elevated above the U.S. FDA action level (1 μg/g Hg) in 7% of the fish sampled or in one or more individual fish from 9 of the 16 lakes sampled. Fish Hg concentrations generally increased with increasing fish length, weight and age. Patterns of increasing Hg concentration with age likely reflect shifts in prey of yellow perch and the bioconcentration of Hg along the food chain. For age 3 to 5 perch, concentrations of Hg increased with increasing concentrations of DOC and percent near-shore wetlands in the drainage basin. However, for a lake with very high DOC concentrations, fish concentrations of Hg declined. Calculations with the MCM also show that concentrations of Hg species increase with increasing DOC due to complexation reactions. Increases in DOC result in increasing concentrations of Hg in biota but decreases in the bioconcentration factor of Hg in fish tissue. This research suggests that DOC is important in the transport of Hg to lake systems. High concentrations of DOC may complex MeHg, diminishing its bioavailability. At high concentrations of monomeric Al, the complexation of MeHg with DOC apparently decreases, enhancing the bioavailability of MeHg.     

Total cadmium concentrations in the water and littoral sediments of Central Ontario Lakes

Lakes within 20 km of Sudbury, Ontario, have significantly higher Cd concentrations in surface waters (geometric mean 122 ng L^?1; n = 7) than lakes elsewhere in central Ontario (10.8 ng L^?1; n = 57). Cadmium concentrations in water from lakes beyond the Sudbury halo were negatively correlated (r = 0.797; p < 0.001) with pH. A weak correlation between fluoride and Cd concentrations leads to speculation that some Cd may be mobilized from watersheds with Al. Cadmium concentrations in littoral sediments are not elevated near Sudbury. The geometric mean Cd concentration of littoral sediments in central Ontario lakes is 0.08 mg Cd kg^?1 dry mass (n = 75). Cadmium concentrations in littoral sediments are strongly correlated with sediment loss on ignition (r = 0.860; p < 0.001). After correction for differences in organic content, littoral sediments are less enriched with Cd than profundal sediments, as reported in the literature. The difference between littoral and profundal sediments, and the sensitivity of Cd concentrations in water to pH, may be due to the importance of Cd binding by Fe/Mn hydrous oxides in the profundal zone, while organic matter binds Cd in the littoral zone. The lack of sensitivity of Cd concentrations in littoral sediments to acidification may be due to the incorporation of much of the Cd in those sediments into organic particulates.     

Effect of pH on the bioaccumulation of low level,dissolved methylmercury by rainbow trout (Oncorhynchus mykiss)

An inverse relationship has been observed between pH and McHg concentration in freshwater fish. Many hypotheses exist regarding the mechanisms which lead to elevated levels of organic Hg in fish from low pH lakes. To determine if pH has a direct effect on the rate of McHg bioaccumulation in fish, rainbow trout fingerlings (Oncorhynchus mykiss) were exposed to a low concentration of aqueous methylmercuric chloride (1.38 ± 0.49 ng·L^?1) at four pH-levels (8.2, 7.0, 6.3, 5.8) for eight weeks. McHg and total Hg were specifically determined on whole fish homogenates and water samples. The pH was found to have a significant: inverse effect on the rate of McHg bioaccumulation in the fish only in the lowest exposure level. Fish held at pH 5.8 had an uptake rate of 1.11 ± 0.07 ng·g^?1·d^?1, while those at pH ≥ 6.3 had a MeHg tissue uptake rate of ≤ 0.64 ± 0.07 ng·g^?1·d^?1. Total body burden of MeHg in the fish held at pH 5.8 also showed an elevated level of MeHg when compared with fish held at higher pH-levels, but the difference was less dramatic. These results suggest that a portion of the Hg burden in fish from low pH systems may be due to the direct effects of low pH on bioaccumulation, but that a threshold may exist above which pH does not play a significant role.     

Perch mercury content is related to acidity and color of 26 Russian lakes

We determined mercury in fish (perch Perca fluviatilis) from 26 Russian lakes in three regions over four years. The lakes ranged in size from 2 to 395,000 ha, in pH from 4.5 to 10.0, and in color from 3 to 190 hazen. Sixteen lakes were drainage lakes, with permanent outlets, and 10 were seepage lakes, with no permanent inlets or outlets. The lakes were generally located in forested regions with little or no human habitation in the watershed. The three regions were geologically distinct: Precambrian Shield granitic bedrock covered with thin soil; Triassic bedrock covered with thick glacial tills; and Triassic bedrock covered with thin sediments. At each lake water samples were collected and analyzed for pH, add neutralizing capacity (ANC), major cations, and anions. Dissolved mercury species were estimated with a thermodynamic equilibrium model (MINTEQA2). Mercury content of dorsal muscle varied from 0.04 to 1.0 g/g wet weight, and was linearly related to calculated HgCH₃Cl (r²0.68, p<0.001). lake=">₃Cl, in turn, was related to lake pH (r²=0.86, p<0.001). stepwise=" multiple=" regression=" selected=" lake=">₃Cl and color as the factors most highly related to fish mercury content, with the model accounting for 75% of the variation.     

Total concentrations of mercury in Wisconsin (USA) lakes and rivers

We analyzed surface waters from 30 Wisconsin lakes and rivers for total mercury ([Hg]_T) and total suspended particulates (TSP) on a state-wide basis with trace-metal ‘ultraclean’ techniques. Mercury concentrations ranged from 0.3 to 2.9 ng L^?1 in lakes and from 0.7 to 8.9 ng L^?1 in rivers. TSP concentrations ranged from 0.9 to 6.6 mg L^?1 in lakes and from 3.1 to 31.4 mg L^?1 in rivers. Spatial trends were weak; however, [Hg] _T was generally higher in the spring than in the autumn of 1991. Total mercury concentration was weakly dependent on TSP with the coefficient of determination (r ²) ranging 0.06 to 0.49 across seasonal and geophysical differences.     

Fish responses to acidity in Québec lakes: A review

To establish the impact of acidity on fish populations,studies were conducted in 37 Québec lakes located in four regions; the réserve des Laurentides and Portneuf and the Charlevoix and Témiscamingue regions. Density (catch per unit effort) of brook chary (Salvelinus fontinalis) decreases with increasing acidity. Moreover, in the Charlevoix region, this species has disappeared from three acid lakes (4.6 ?pH?5.l) with low Ca levels. Unlike growth, condition demonstrates a close relationship to acidity in brook charr populations. The total Al concentration in gills decreases with increasing size and pH. Lake acidity and sensitivity to acidification introduces problems in gamefish management. A survey of 17 lakes of the Témiscamingue region reveals that species diversity and total fish biomass are much lower in acid lakes than non acid lakes. In addition, two acid lakes are devoid of fish. Cyprinidae and Johnny darters (Etheostoma nigrum) are abundant in lakes with a pH level of 5.9 to 7.0 but are absent in lakes with a pH lower than 5.2. The yellow perch (Perca flavescens) is the only fish that appears to be tolerant to a wide pH range. This species, however, is in poor condition in acid lakes as compared with non acid lakes.     

Common loons (Gavia immer) nesting on low ph lakes in northern Wisconsin have elevated blood mercury content

The Wisconsin Department of Natural Resources conducted a pilot study during the summer of 1991 to determine the extent of mercury (Hg) exposure in common loons (Gavia immer) breeding in Wisconsin. Loons are at risk to elevated Hg exposure in Wisconsin because they often nest on acidified, low alkalinity lakes. Fish from these lakes bioaccumulate MeHg to a greater extent than biota from neutral pH lakes. Using nightlighting techniques, 35 adult loons were captured on 20 northern Wisconsin lakes (pH=5.0–8.7) in 1991. Blood and feather samples were collected for Hg analysis. The mean Hg content of blood cells collected from adult loons on low pH lakes (pH≤6.3) was significantly greater than the Hg content of adult loons collected on neutral/alkaline pH lakes (pH>-7.0) (F=19.87, P<0.001). There was a highly significant negative linear relationship between adult loon blood cell Hg concentrations and lake pH (r²=0.38, F=15.27, P>0.001); indicating loons nesting on low pH lakes receive greater Hg exposure than loons nesting on neutral pH lakes. The relationship was greater amongst adult males (r²=0.56) than amongst adult females (r²=0.36). Because of this documented exposure, an additional 330 loons were captured 1992-94 on 73 lakes in northern Wisconsin. The Hg exposure of adult and juvenile common loons is being quantified. Individual loons were fitted with unique color-coded leg bands, and the 1992–96 reproductive performance, apnual return rates, and nesting behavior of adult loons with the known Hg exposure is currently being assessed.