Mercury in Tadpoles Collected from Remote Alpine Sites in the Southern Sierra Nevada Mountains, California, USA

Abstract

Amphibians in alpine wetlands of the Sierra Nevada mountains comprise key components of an aquatic-terrestrial food chain, and mercury contamination is a concern because concentrations in fish from this region exceed thresholds of risk to piscivorous wildlife. Total mercury concentrations were measured in whole tadpoles of the Sierra chorus frog, Pseudacris sierra, two times at 27 sites from high elevations (2786-3375 m) in the southern Sierra Nevada. Median mercury concentrations were 14 ng/g wet weight (154 ng/g dry weight), which were generally low in comparison to tadpoles of 15 other species/location combinations from studies that represented both highly contaminated and minimally contaminated sites. Mercury concentrations in P. sierra were below concentrations known to be harmful in premetamorphic tadpoles of another species and below threshold concentrations for risk to predaceous wildlife. Concentrations in tadpoles were also lower than those observed in predaceous fish in the study region presumably because tadpoles in the present study were much younger (1-2 months) than fish in the other study (3-10 years), and tadpoles represent a lower trophic level than these fish. Mercury concentrations were not related to distance from the adjacent San Joaquin Valley, a source of agricultural and industrial pollutants.

Survey of mercury in boreal chorus frog (Pseudacris maculata) and wood frog (Rana sylvatica) tadpoles from wetland ponds in the Prairie Pothole Region of Canada

“…Lower values were not outside the range of those measured in other studies; however, upper values exceeded those of any previous study, including in amphibians from some contaminated studies (see Bradford et al 2012 for a summary). The variables species, stage, and mass explained 21% of total variation for body burden in our models but had negligible predictive ability for THg concentration (Table S3).…”

“…This may be due to life history parameters such as stage of development, because greater development leads to more opportunity for Hg biomagnification and a change in diet as the organism approaches metamorphosis (Bradford et al 2012). To address differences in development timelines, we tested the effect of metamorphic stage on body burden and THg concentration.…”

“…Thus, lower trophic levels can mediate the transfer of MeHg from aquatic to terrestrial ecosystems (Bank et al 2007a). Although tadpoles are important prey for many fish and waterfowl (Bergeron et al 2010b), there is a lack of studies focused on amphibians compared with other aquatic vertebrates (Bradford et al 2012). Furthermore, tadpole biomass is often the largest of all vertebrates in many fishless wetland ecosystems, making them an important part of ecosystem functioning (Ugarte et al 2005).…”

Complex Life Histories Alter Patterns of Mercury Exposure and Accumulation in a Pond-Breeding Amphibian

“…Amphibians face an array of conservation threats, including exposure to contaminants such as Hg. ,− Research suggests that tadpoles can eliminate inorganic Hg from their tissues but retain MeHg at metamorphosis . If bioaccumulated MeHg concentrations are high enough, development and metamorphic success can be adversely affected .…”

Inorganic Chemistry in the Mountain Critical Zone

“…On the other hand, no clear evidence exists of a gradient impact of Hg transfer in amphibians from the Sierra Nevada. Also no evidence occurs of hot spots of mercury concentrations in tadpoles in the Sierra Nevada due to the transportation of atmospheric Hg from the nearby San Joachim valley (Bradford et al, 2012). Clocks indicate environmental archives but also potential reservoir compartments for anthropogenic potentially harmful trace element (PHTE).…”