Assessment of mercury bioaccumulation within the pelagic food web of lakes in the western Great Lakes region (original) (raw)
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Niche segregation between introduced and native fish in Lake Nahuel Huapi, a deep oligotrophic lake in Northwest Patagonia (Argentina), occurs through the consumption of different prey. Therefore, in this work we analyzed total mercury [THg] and methylmercury [MeHg] concentrations in top predator fish and in their main prey to test whether their feeding habits influence [Hg]. Results indicate that [THg] and [MeHg] varied by foraging habitat and they increased with greater percentage of benthic diet and decreased with pelagic diet in Lake Nahuel Huapi. This is consistent with the fact that the native creole perch, a mostly benthivorous feeder, which shares the highest trophic level of the food web with introduced salmonids, had higher [THg] and [MeHg] than the more pelagic feeder rainbow trout and bentho-pelagic feeder brown trout. This differential THg and MeHg bioaccumulation observed in native and introduced fish provides evidence to the hypothesis that there are two main Hg transfer pathways from the base of the food web to top predators: a pelagic pathway where Hg is transferred from water, through plankton (with Hg in inorganic species mostly), forage fish to salmonids, and a benthic pathway, as Hg is transferred from the sediments (where Hg methylation occurs mostly), through crayfish (with higher [MeHg] than plankton), to native fish, leading to one fold higher [Hg].
Bioaccumulation of mercury in pelagic freshwater food webs
Science of The Total Environment, 1998
Current paradigms regarding the bioaccumulation of mercury are rooted in observations that monomethyl mercury Ž . meHg biomagnifies along pelagic food chains. However, mechanisms regulating the formation of meHg, its initial incorporation at the base of pelagic food chains, and its subsequent trophic transfer remain controversial. Here we use field data from 15 northern Wisconsin lakes, equilibrium aqueous speciation modeling, and statistical modeling Ž II . to revisit several hypotheses about the uptake, distribution, and fate of inorganic Hg Hg and meHg in aquatic Ž . biota. Our field data comprise determinations of total Hg Hg and meHg in surface waters, sediments, microseston, U Corresponding author.
An investigation of enhanced mercury bioaccumulation in fish from offshore feeding
Ecotoxicology, 2013
We investigated the dietary pathways of mercury transfer in the food web of Morency Lake (Canada) to determine the influence of carbon source and habitat use on mercury bioaccumulation in fish. Whole-body concentrations of methylmercury (MeHg) were significantly different in four fish species (white sucker, brown bullhead, pumpkinseed and smallmouth bass) and increased with both trophic position and greater feeding on offshore (versus littoral) carbon. An examination of fish gut contents and the depth distribution of invertebrates in Morency Lake showed that smallmouth bass and brown bullhead were supplementing their littoral diet with the consumption of either opossum shrimp (Mysis diluviana) or profundal amphipods in offshore waters. The zooplanktivore Mysis had significantly higher MeHg concentrations than zooplankton and benthic invertebrates, and it was an elevated source of MeHg to smallmouth bass. In contrast, profundal amphipods consumed by brown bullhead did not have higher MeHg concentrations than littoral amphipods. Instead, partitioning of benthic invertebrate resources likely explains the greater MeHg bioaccumulation in brown bullhead, associated with offshore feeding of amphipods. White sucker and brown bullhead had a similar trophic position but white sucker consumed more chironomids, which had one-third the MeHg concentration of amphipods. Our findings suggest that offshore feeding in a lake can affect fish MeHg bioaccumulation via two different processes: (1) the consumption of MeHg-enriched pelagic prey, or (2) resource partitioning of benthic primary consumers with different MeHg concentrations. These observations on the mechanisms of habitat-specific bioaccumulation highlight the complexity of MeHg transfer through lake food webs.
Journal of Great Lakes Research, 2019
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 lm) 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.
Transfer of mercury in the food webs of Lake St-Pierre
For human populations, the main way of contamination by mercury (Hg) is through the consumption of fish. In Quebec (Canada), annually, there are 1387 tons of freshwater fish caught each year by professional fishermen, more than half of the catches are from Lake St.-Pierre, a widening of the St.-Lawrence River. Despite the fact that this lake receives high inputs of Hg their fish have much lower concentrations than in Canadian boreal lakes for the same species and standardized fish length. The classical Hg path, sediment, deep benthos or zooplankton could not explain the low fishs Hg concentrations in Lake St.-Pierre. Our working hypothesis to explain the observed differences is based on littoral trophic approach. Indeed, we think that the uniqueness of Lake St.-Pierre is the dominance of the littoral zone which has very complex trophic web and can bear several trophic bottlenecks. This means that in the littoral zone, many organisms, mainly invertebrates occupying high trophic levels are not equally consumed by fish. The preliminary results of our study seems to indicate that the inedible macroinvertabres had the highest THg concentrations.
Limnology and Oceanography, 1998
Seasonal concentration changes in monomethylmercury (MMHg) and total Hg (T-Hg) were determined in Devil's Lake, Wisconsin, a lake with a mercury consumption advisory for walleye. Mercury dynamics were studied in water and several lower food chain fractions during the ice-free seasons in 1994 and 1995, and limited data for Hg in water were collected in 1993. MMHg concentrations increased in hypolimnetic waters before turnover each year, although maximum concentrations declined from 1993 to 1995. As the hypolimnion eroded, MMHg concentrations increased in both particulate matter and Daphnia. Maximum concentrations were obtained near the time of complete mixis. The magnitude of this increase correlated with the mass of hypolimnetic MMHg that had built up prior to turnover in 1994 and 1995. Hg concentrations in yearling planktivorous fish exhibited a decline corresponding to the decline in hypolimnetic MMHg from 1993 to 1995. Our results suggest that fall destratification represents an important time period for entry of MMHg to the food chain of lakes exhibiting a hypolimnetic MMHg buildup.
Proceedings of the National Academy of Sciences, 2019
To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ202Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ202Hg indicate fish are responding to seve...
Science of The Total Environment
Dietary uptake is a key step in conveying both toxic mercury (Hg; particularly as highly bioavailable methylmercury, MeHg) and essential dietary biochemicals, such as polyunsaturated fatty acids (PUFA), across trophic levels within aquatic food webs. Using stable isotopes and fatty acids we evaluated the role of food sources in size-fractioned plankton and littoral macroinvertebrates for the bioaccumulation of total Hg and MeHg in six oligotrophic and one mesotrophic Swedish lakes with differing concentrations of dissolved organic carbon (DOC). We found that the consumption of both algal and terrestrial diets (assessed by PUFA and long-chain saturated fatty acids, respectively) predicted >66% of the Hg concentration variability in meso-(100-500 µm) and macrozooplankton (>500 µm) in oligotrophic lakes. In the mesotrophic lake, total Hg bioaccumulation in higher trophic level biota, carnivorous macroinvertebrates was also significantly related to terrestrial diet sources (R 2 =0.65, p<0.01). However, lake pH and DOC correlated to total Hg bioaccumulation and bioconcentration across all lakes, suggesting the consumption of different diet sources is mediated by the influence of lake characteristics. This field study reveals that using dietary biomarkers (stable isotopes and fatty acids) together with the physico-chemical lake parameters pH and nutrients together improve our ability to predict Hg bioaccumulation in aquatic food webs. Fatty acids used as dietary biomarkers provide correlative evidence of specific diet source retention in consumers and their effect on Hg bioaccumulation, while pH and nutrients are the underlying physico-chemical lake parameters controlling differences in Hg bioaccumulation between lakes.
Factors affecting enhanced mercury bioaccumulation in inland lakes of Isle Royale National Park, USA
The Science of the total environment, 2003
We investigated factors causing mercury (Hg) concentrations in northern pike to exceed the consumption advisory level ()500 ngyg) in some inland lakes of Isle Royale National Park. Using Hg-clean techniques, we collected water, zooplankton, macro invertebrates, and fishes in 1998 and 1999 from one advisory lake, Sargent Lake, for analysis of total mercury (Hg ) and methylmercury (MeHg). For comparison, samples were also collected from a T non-advisory lake, Lake Richie. Concentrations of Hg in northern pike were significantly higher in Sargent Lake T (P-0.01). Counter to expectations, mean concentrations of both Hg and MeHg in open water samples were slightly T higher in Lake Richie. However, zooplankton in Sargent Lake contained higher average concentrations of Hg and T MeHg than in Lake Richie. Mercury concentrations in macro invertebrates were similar between lakes, but different between taxa. The two lakes exhibited similar Hg concentrations in age-1 yellow perch and adult perch but T concentrations in large adult perch ()160 mm) in Sargent Lake were twice the concentrations in Lake Richie. Analysis of stable isotopes (d C and d N) in biota showed that pike from the two lakes are positioned at the same 13 15 trophic level (4.2 and 4.3), but that the food web is more pelagic-based in Sargent and benthic-based in Richie. Factors causing concentrations in large pike to be higher in Sargent Lake may include higher bioavailability of methylmercury and a food web that enhances bioaccumulation. ᮊ