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The biomagnification of toxic methylmercury (MeHg) and selenium (Se) through aquatic food webs using nitrogen stable isotopes (δ15N) varies among ecosystems but underlying mechanisms are yet unexplained. Given the strong links between MeHg and thiol-containing amino acids and proteins containing selenocysteine, our hypothesis was that cysteine content is a better predictor of MeHg and Se transfer through lake food webs than δ15N. Food web samples were collected from six lakes in Kejimkujik National Park, Nova Scotia, Canada, and the regression slopes of log MeHg or Se versus protein-bound cysteine or bulk δ15N were compared. Across all six lakes, MeHg varied by a factor of 10 among taxa and was significantly and positively related to both cysteine (R2 = 0.65–0.80, p < 0.001) and δ15N (R2 = 0.88–0.94, p < 0.001), with no among-system differences in these slopes. In contrast, total Se concentrations varied by less than a factor of 2 among taxa in four lakes and were significantly related to cysteine in only two food webs (R2 = 0.20 & 0.37, p = 0.014 & < 0.001); however, δ15N was not a predictor of Se in any lake (p = 0.052–0.777). Overall, these novel results indicate that cysteine content predicts MeHg, and sometimes Se, across trophic levels, providing a potential mechanism for among-system differences in their biomagnification. [Display omitted] • Biomagnification of methylmercury (MeHg) and selenium (Se) varies among food webs. • Models of their trophic transfer compared using δ15N and S-containing amino acids. • Cysteine content was a strong predictor of MeHg within all 6 lake food webs. • Model comparisons indicated MeHg biomagnification was best explained by δ15N. [ABSTRACT FROM AUTHOR]

Seabirds are important biovectors of contaminants, like mercury, moving them from marine to terrestrial environments around breeding colonies. This transfer of materials can have marked impacts on receiving environments and biota. Less is known about biotransport of contaminants by generalist seabirds that exploit anthropogenic wastes compared to other seabird species. In this study, we measured total mercury (THg) in O-horizon soils at four herring gull (Larus smithsoniansus) breeding colonies in southern Nova Scotia, Canada. At colonies with dry substrate, THg was significantly higher in soils collected from gull colonies compared to nearby reference soils with no nesting gulls. Further, THg was distinct in soils among study colonies and was likely influenced by biotransport from other nesting seabird species, most notably Leach's storm-petrels (Hydrobates leucorhous). Our research suggests gulls that scavenge on anthropogenic wastes at local industrial sites are biovectors moving THg acquired at these sites to their colonies and may increase the spatial footprint of contaminants from these industries. [Display omitted] • Gulls feeding on anthropogenic industrial wastes may be exposed to mercury. • Gull colony soils showed elevated levels of THg. • Soil at gull colonies suggest biotransport of regional THg. [ABSTRACT FROM AUTHOR]

Soils are a source of elemental mercury (Hg(0)) to the atmosphere, however the effects of soil temperature and moisture on Hg(0) formation is not well defined. This research quantifies the effect of varying soil temperature (278–303 K), moisture (15–80% water filled pore space (WFPS)) and sterilization on the kinetics of Hg(0) formation in forested soils of Nova Scotia, Canada. Both, the logarithm of cumulative mass of Hg(0) formed in soils and the reduction rate constants ( k values) increased with temperature and moisture respectively. Sterilizing soils significantly ( p < 0.05, n = 10) decreased the percent of total Hg reduced to Hg(0). We describe the fundamentals of Hg(0) formation in soils and our results highlight two key processes: (i) a fast abiotic process that peaks at 45% WFPS and depletes a small pool of Hg(0) and; (ii) a slower, rate limiting biotic process that generates a large pool of reducible Hg(II). [ABSTRACT FROM AUTHOR]

Quantifying methylmercury (MeHg) concentrations and uptake at the base of the food web is useful for assessing mercury exposure risk to higher trophic level organisms. Higher MeHg concentrations near the base of the food web may result in more MeHg exposure and accumulation in higher trophic organisms. Here, we analyze MeHg in caddisflies, mayflies, lake water, and sediment collected from two temperate lakes and one brook in Kejimkujik National Park, Nova Scotia, Canada. Overall, caddisfly larvae MeHg (15.38–276.96 ng/g; n = 29) was not significantly correlated with water chemistry. Whereas mayfly naiads MeHg (14.28–166.82 ng/g; n = 31) was positively correlated with water MeHg (r s = 0.43), negatively correlated with pH (r s = −0.49), and positively correlated with dissolved organic carbon (DOC; r s = 0.48). Of the mercury in insect tissues, the %MeHg ranged from 56 to 75 % in caddisfly larvae and 38–47 % in mayfly naiads. MeHg bioaccumulation factors (BAF) varied greatly (water to tissue BAFs = 0.145 × 106–1.054 × 106; sediment to tissue BAFs = 0.017 × 106–0.541 × 106). This study highlights the importance of quantifying variations in MeHg bioaccumulation and BAFs of common aquatic insect bioindicators at the base of complex food webs. [Display omitted] • Mayfly MeHg was more influenced by water than sediment. • Caddisfly larvae MeHg may be more influenced by sediment than water. • Each invertebrate type had wide %MeHg ranges likely due to feeding ecology. • Caddisflies and mayflies are good indicators of methylmercury loading to food webs. • Adult caddisflies and mayflies efficiently transfer MeHg to terrestrial food webs. [ABSTRACT FROM AUTHOR]

The use of naturally occurring epiphytic lichens can be an effective tool for regional monitoring of mercury (Hg) and other potentially toxic elements (PTEs). Nova Scotia, Canada is a hotspot for mercury and other trace metal accumulation in ecosystems; partially attributed to long-range transport of air pollution. The relative contribution of local and international sources of Hg to local air in Nova Scotia is unknown. This study assessed the potential of epiphytic lichens (Usnea spp.) as passive samplers for PTE air pollution in Nova Scotia. Lichens (n = 190) collected across mainland Nova Scotia were analyzed for PTEs. Results indicate that there are 3 distinct clusters of PTEs which suggest patterns and sources for each elemental cluster. Hg was correlated with longitude and prevailing wind direction, and Hg was not significantly different in site-specific hotspot sampling nor year of sampling. Our data support the hypothesis that Hg in lichens is from historical and ongoing long-range transport and diffuse emission patterns rather than localized pollution sources. PTE concentrations were shown to have median values that are similar to other remote regions (such as the Antarctic) however the maximum values were observed to be substantially higher for some elements (e.g. lead, cadmium). This research supports the use of lichens as biomonitors and provides a baseline for future monitoring efforts to identify changes in PTE distribution in Nova Scotia with ongoing industrial activity and a changing climate. Image 10804 • Epiphytic lichens were used as passive samplers for air pollution. • Data support the hypothesis that lichen Hg is from historical long-range transport. • Potentially toxic elements had concentrations similar to other remote regions. • Element clustering indicated both long-range atmospheric and mineral sources. • Provides baseline data for identifying changes in trace metal distribution. Spatial variability of potentially toxic elements (PTEs) can be monitored using epiphytic lichens to make inferences on source, be it long range transport, nearby pollution, or local mineralogy. [ABSTRACT FROM AUTHOR]