Emergent Freshwater Insects Serve as Subsidies of Methylmercury and Beneficial Fatty Acids for Riparian Predators Across an Agricultural Gradient.

Aquatic-to-terrestrial subsidies have the potential to provide riparian consumers with benefits in terms of physiologically important organic compounds like omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs). However, they also have a "dark side" in the form of exposure to toxicants such as mercury. Human land use intensity may also determine whether subsidies provide benefits or come at a cost for riparian predators. We sampled insects as well as Eastern Phoebe (Sayornis phoebe) chicks in 2015-2016 within the southern Finger Lakes region to understand how food quality, in terms of n-3 LCPUFAs and methylmercury (MeHg), of emergent freshwater insects compared with that of terrestrial insects and how land use affected the quality of prey, predator diet composition, and MeHg exposure. Across the landscape, freshwater insects had a significantly higher percentage of the n-3 LCPUFA eicosapentaenoic acid (EPA) compared to terrestrial insects and contained significantly more MeHg than terrestrial insects did. In spite of differences in MeHg concentrations between aquatic and terrestrial insects, chick MeHg concentrations were not related to diet composition. Instead, chick MeHg concentrations increased with several metrics of human land use intensity, including percent agriculture. Our findings suggest that freshwater subsidies provide predators with both risks and benefits, but that predator MeHg exposure can vary with human land use intensity.

Mercury Concentrations in Big Brown Bats (Eptesicus fuscus) of the Finger Lakes Region, New York.

The northeastern United States receives elevated mercury (Hg) deposition from United States and global emissions, making it critical to understand the fate of Hg in watersheds with a variety of aquatic habitats and land use types, such as the Finger Lakes region of New York State. Bats are valuable and important organisms to study chronic Hg exposure, because they are at risk of sublethal effects from elevated Hg exposure. The objectives of this study were to: (1) determine total Hg (THg) and methylmercury (MeHg) concentrations in big brown bats (Eptesicus fuscus) of the Finger Lakes region; (2) assess whether morphometric, temporal, or spatial factors predict bat Hg concentrations; and (3) investigate the role of trophic position and diet represented by stable isotopes of carbon and nitrogen in explaining variations in bat Hg concentrations. We found comparable THg and MeHg concentrations to previous studies (THg range 1-45 ppm, MeHg range 0.5-38 ppm) in big brown bat fur collected throughout the Finger Lakes region. On average, MeHg made up 81% of THg in bat fur. Fifteen percent of our samples showed higher THg than a proposed toxicity threshold of 10 ppm. Together, dominant land cover and % wetland cover explained bat THg in the Finger Lakes. Trophic position (i.e., δ15N) was strongest in predicting bat THg in forests but was a weaker predictor of Hg bioaccumulation in bats from agricultural and urban areas. The range of Hg concentrations found in this study warrants further examination into the potential toxicological impacts of Hg to wildlife and the role of land use in Hg exposure to terrestrial organisms of the Finger Lakes.

Reconstructing avian mercury concentrations through time using museum specimens from New York State.

We examined how variation in MeHg concentrations through time is reflected in birds, a taxon commonly used as a biological indicator of ecosystem health. Using museum specimens collected from 1880 to 2016, we measured feather MeHg concentrations in six species of birds that breed in New York State and have distinct dietary and habitat preferences. We predicted that MeHg concentrations in feathers would mirror Hg emission patterns in New York State and increase through time until 1980 then decrease thereafter in response to increased regulation of anthropogenic Hg emissions. We found that MeHg concentrations increased with δ15N, and that MeHg feather concentrations for some individuals from four of the six species examined exceeded concentrations known to cause negative sublethal effects in birds. In contrast to our prediction, MeHg concentrations in feathers did not parallel global or local Hg emissions through time and varied by species, even after controlling for possible changes in diet and habitat. MeHg concentrations varied substantially within species and individual specimens, suggesting that high within-individual variation in feather MeHg concentrations caused by spatiotemporal variation in molt, environmental Hg exposure, or mobility decoupling Hg uptake from breeding sites, may obscure trends in MeHg through time. Our study provides a unique assessment of feather MeHg in six species not typically analyzed using this retrospective approach.

Mercury in fish from streams and rivers in New York State: Spatial patterns, temporal changes, and environmental drivers.

Mercury (Hg) concentrations in freshwater fish across the state of New York frequently exceed guidelines considered harmful to humans and wildlife, but statewide distribution and temporal changes are not well known for the state's streams and rivers. We analyzed existing data to describe recent spatial patterns, identify key environmental drivers, and assess temporal changes. Size classes within sportfishes and prey fishes formed 'functional taxa' (FT), and standardized scores were generated from 2007-2016 data for 218 sites. Muscle Hg in ≥1 sportfish FT exceeded human-health guidelines of 50 ng/g (sensitive populations) and 300 ng/g (general population, GP) at 93 and 56% of sites, respectively, but exceeded 1000 ng/g (a state threshold) at only 10% of sites. Whole-body Hg in ≥1 prey fish FT exceeded wildlife thresholds of 40 ng/g and 100 ng/g at 91 and 51% of sites, respectively. Environmental drivers of recent spatial patterns include extent of forest cover and storage, the latter an indicator of wetlands. Standardized Hg scores increased with increasing atmospheric Hg deposition and storage across rural 'upland' regions of New York. However, scores were not related to atmospheric deposition in more-developed 'lowland' regions due to the limited methylation potential of urban landscapes. Comparisons of 2010-2015 sportfish Hg concentrations with those of 1998 and 2000-2005 showed inconsistent temporal changes both among and within eight sites examined. Some recent stream and river fish Hg spatial patterns differed from those of lake-based studies, highlighting the importance of New York's flowing waters to future Hg monitoring and risk assessment.

Mercury concentrations in fish and invertebrates of the Finger Lakes in central New York, USA.

Deleterious health effects in humans and wildlife are associated with the consumption of fish contaminated by mercury (Hg). This study was conducted to assess Hg concentrations in biota of the Finger Lakes (New York, USA), a region where fisheries are important for the economy but where no assessment of the drivers of food web Hg dynamics exists to date. Additionally, this region is of interest for the study of Hg bioaccumulation because of the importance of agricultural land cover, which can affect lake trophic status and thus the bioavailability of methyl Hg (MeHg). The study objectives were to (1) assess if fish Hg concentrations were of concern to humans and wildlife, (2) determine if differences in biota Hg concentrations exist among lakes, and (3) assess models developed for New York State as predictors of present day Finger Lakes fish Hg concentrations. Exploratory analyses were also conducted to assess predictors of fish Hg concentrations using lower trophic level MeHg concentrations, water quality, and lake and land cover characteristics. Fish concentrations were above the EPA criterion (300 ng/g wet weight, ww) in 24% of fish, but only Walleye (Sander vitreus) from Owasco Lake exceeded New York State Department of Health consumption guidelines (1000 ng/g ww). The threshold indicating biological changes within fish (500 ng/g ww) was exceeded in 11% of the individuals sampled. Significant differences were found among lakes for all fish species except Largemouth Bass (Micropterus salmoides). Notably, Lake Trout (Salvelinus namaycush) had significantly lower Hg concentrations in Cayuga Lake compared to other Finger Lakes. This trend was not mirrored in the lower food web, as benthic invertebrates had higher MeHg concentrations in Cayuga Lake. Using models developed for New York State in 2003-2005, observed concentrations in 90% of fish were different (±200 ng/g ww) than expected. Findings from this study suggest Hg dynamics in the Finger Lakes require consideration of fish age, growth rates, and food web structure to accurately predict fish Hg concentrations among lakes.

Mercury bioaccumulation in stream food webs of the Finger Lakes in central New York State, USA.

Studies of mercury (Hg) bioaccumulation in streams draining both forested and agricultural watersheds are not common. Sixteen streams were sampled in the Finger Lakes region in central New York State with a mean agricultural land cover of 48%. Stream fish (Blacknose Dace, Rhinichthys atratulus, an invertivore; and Creek Chub, Semotilus atromaculatus, an omnivore) were collected and analyzed for total Hg (THg), and macroinvertebrates and periphyton were collected and analyzed for methylmercury (MeHg) determination. The effect of water chemistry, land cover, and macroinvertebrate MeHg was assessed as predictors of fish Hg concentrations. Blacknose Dace had significantly higher THg concentrations compared to Creek Chub (229 ng/g vs. 195 ng/g dry weight, respectively), and predatory and omnivorous macroinvertebrates (i.e., Perlidae and Cambaridae) were found to have significantly higher MeHg concentrations compared to other functional feeding groups. Mixed effects models identified macroinvertebrate MeHg concentrations as predictors of stream fish THg concentrations. Partition modeling found fish total length and total suspended solids predicted Blacknose Dace with 'High' vs 'Low' Hg (≥ or < 90 ng/g wet weight, respectively). Overall, stream fish THg concentrations observed were not of concern, unlike other regions in New York State such as the Adirondack Mountains, but a significant proportion of Blacknose Dace (22 - 73%) and Creek Chub (5 - 69%) would be considered a risk to a range of sensitive consumers.

Factors affecting enhanced mercury bioaccumulation in inland lakes of Isle Royale National Park, USA.

We investigated factors causing mercury (Hg) concentrations in northern pike to exceed the consumption advisory level (>500 ng/g) 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(T)) and methylmercury (MeHg). For comparison, samples were also collected from a non-advisory lake, Lake Richie. Concentrations of Hg(T) in northern pike were significantly higher in Sargent Lake (P<0.01). Counter to expectations, mean concentrations of both Hg(T) and MeHg in open water samples were slightly higher in Lake Richie. However, zooplankton in Sargent Lake contained higher average concentrations of Hg(T) and MeHg than in Lake Richie. Mercury concentrations in macro invertebrates were similar between lakes, but different between taxa. The two lakes exhibited similar Hg(T) concentrations in age-1 yellow perch and adult perch but concentrations in large adult perch (>160 mm) in Sargent Lake were twice the concentrations in Lake Richie. Analysis of stable isotopes (delta(13)C and delta(15)N) in biota showed that pike from the two lakes are positioned at the same 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.

Mercury content and speciation in the plankton and benthos of Lake Superior.

As part of a study is to assess the importance of watersheds in controlling sources, transport, fate, and bioavailability of monomethyl mercury (MeHg) in Lake Superior, biotic samples were collected and analyzed to determine total mercury (HgT) and MeHg content, and to examine size, species, trophic and geographic trends. Plankton was collected in two ways: vertical tows of non-metallic, 153 microm mesh net (bulk zooplankton), and by passively filtering near-surface water through stacked Nitex sieves, generating size-fractionated seston (<35, 35-63, 63-112, and >112 microm). Benthos was sampled using a Ponar grab to collect sediment, and a non-metallic sieve to separate biota from substrate. Samples were processed to quantify dry weights, HgT and MeHg. Results for bulk zooplankton sampled offshore showed a range of approximately from 35 to 50 ng MeHg/gram dry weight (gdw) and from 80 to 130 ng HgT/gdw during April, and from 15 to 25 ng MeHg/gdw and from 20 to 70 ng HgT/gdw during August. Results from sieved, near-surface water from offshore sites in April showed a dominance by the <35 microm size fraction both in total mass and mass of MeHg compared to other size fractions. On a dry weight basis, however, we found little difference between the size fractions in April (MeHg ranges from 2 to 10 ng/gdw). During the summer cruise, we found similar concentrations in the <35 microm fraction, but higher in the 112-243 microm size fraction (MeHg 14-16 ng/gdw). The MeHg concentration in Mysis relicta ranged from 33 to 54 ng/gdw throughout the lake. Chironomid larvae were 8 ng MeHg/gdw and amphipods were 32 ng MeHg/gdw.

Deposition and cycling of sulfur controls mercury accumulation in Isle Royale fish.

Mercury contamination of fish is a global problem. Consumption of contaminated fish is the primary route of methylmercury exposure in humans and is detrimental to health. Newly mandated reductions in anthropogenic mercury emissions aim to reduce atmospheric mercury deposition and thus mercury concentrations in fish. However, factors other than mercury deposition are important for mercury bioaccumulation in fish. In the lakes of Isle Royale, U.S.A., reduced rates of sulfate deposition since the Clean Air Act of 1970 have caused mercury concentrations in fish to decline to levels that are safe for human consumption, even without a discernible decrease in mercury deposition. Therefore, reductions in anthropogenic sulfur emissions may provide a synergistic solution to the mercury problem in sulfate-limited freshwaters.