You are here:
Mercury isotopic signatures are transmitted from aquatic to terrestrial ecosystems
Citation:
Walters, D., S. Janssen, J. Hoffman, M. Mills, Jim Lazorchak, C. Eagles-Smith, G. Peterson, A. Cotter, AND D. Krabbenhoff. Mercury isotopic signatures are transmitted from aquatic to terrestrial ecosystems. SETAC North America, Duluth, MN, November 15 - 19, 2020. https://doi.org/10.23645/epacomptox.13171823
Impact/Purpose:
Mercury (Hg) contamination is widespread within Great Lakes Areas of Concern and a common target for remediation efforts. Mercury can be transported from aquatic to terrestrial food webs via adult aquatic insects. As such, riparian predators such as spiders are increasingly used as indicators of aquatic contamination levels and could be used to determine remedy effectiveness. However, few studies have addressed whether patterns of mercury isotopic variation (as a source-specific signature) in aquatic food webs are transferred to land via the aquatic insect trophic linkage. Our findings indicate that mercury isotope source signatures originating in aquatic food webs are conserved and transferred into riparian ecosystems, demonstrating the export of legacy mercury contamination in river sediments to floodplain food webs. This suggests that mercury isotopes can be used to trace sources in these linked systems and to assess recovery from mercury contamination at local scales following remediation.
Description:
Mercury (Hg) stable isotopes are increasingly used to investigate sources of Hg in the environment and as a tool for assessing remediation effectiveness. Mercury can be transported from aquatic to terrestrial food webs via adult aquatic insects, and riparian predators such as spiders are increasingly used as indicators of aquatic contamination levels. However, few studies have addressed patterns of Hg isotopic variation in aquatic food webs, and whether the patterns found in those systems are transferred to land via the aquatic insect trophic linkage. We measured Hg isotopes in long-jawed spiders (Tetragnthidae) in comparison to benthic invertebrates (e.g., odonates) and prey fish (e.g., cyprinids) within two tributaries to Lake Superior: the St. Louis River spanning from upstream reservoirs to the lower estuary near Duluth, MN and a reference watershed. The lower reaches of the St. Louis River near Duluth Harbor in Lake Superior have documented industrial Hg sources, whereas atmospheric deposition is the only known Hg source in the relatively undeveloped reference watershed. Spatial variation in signatures of δ202Hg were observed in spiders and matched measurements of aquatic species. Depleted δ202Hg values confirmed the predominance of the atmospheric source in the reference watershed, as well as the upper reaches of the St. Louis River. However, more enriched δ202Hg signatures were observed in the lower St. Louis River estuary, confirming the contribution of local industrial Hg sources to aquatic and riparian food webs. Aquatic insect δ202Hg was strongly correlated with fish δ202Hg (r2 = 0.66) and spider δ202Hg (r2 = 0.75). Insect 202Hg was not significantly different than prey fish δ202Hg resulting in a slope of 1.08, suggesting little no isotopic shift during bioaccumulation of Hg within the aquatic food web. Spider δ202Hg was depleted over aquatic insect δ202Hg (~0.15‰), but it is unclear if this depletion resulted during insect metamorphosis, trophic depletion within spiders themselves, or some combination of the two. Our findings indicate that Hg isotope source signatures originating in aquatic food webs are conserved and transferred into riparian ecosystems, demonstrating the export of legacy Hg in river sediments to floodplain food webs. This suggests that Hg isotopes can be used to trace Hg sources in these linked systems and to assess recovery from Hg contamination at local scales following remediation.
URLs/Downloads:
DOI: Mercury isotopic signatures are transmitted from aquatic to terrestrial ecosystems