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Transfer of legacy mercury from aquatic habitats to the terrestrial food web surrounding the St Louis River
Citation:
Janssen, S., D. Walters, J. Hoffman, G. Beaubien, M. Mills, C. Eagles-Smith, D. Krabbenhoft, G. Peterson, AND M. Pearson. Transfer of legacy mercury from aquatic habitats to the terrestrial food web surrounding the St Louis River. St. Louis River Virtual Summit, Duluth, MN, March 01 - 03, 2021. https://doi.org/10.23645/epacomptox.14179289
Impact/Purpose:
Mercury (Hg) is a global pollutant and neurotoxin that has been a focus of environmental remediation for decades owing to its exposure risks for humans and wildlife. There is growing recognition that at contaminated sediment sites, mercury can be transported into the adjacent terrestrial ecosystem. However, this is difficult to measure. We used a mercury stable isotope approach to demonstrate that legacy mercury is being transported from the contaminated sediment into the riparian food web, and also demonstrate the utility of riparian spiders for biomonitoring in this context.
Description:
Mercury (Hg) is a global pollutant and neurotoxin that has been a focus of environmental remediation for decades owing to its exposure risks for humans and wildlife. Within the St. Louis River (SLR) Area of Concern (AOC), there are numerous sources that can contribute to Hg burdens in biota including watershed runoff, offshore precipitation, and legacy contamination located within sediments of the AOC. Legacy contamination has been shown to contribute to Hg levels in benthic insects, prey, and game fish feeding within SLR. However, there is growing recognition that aquatic contaminants, such as Hg, may be transported from aquatic to terrestrial food webs via emerging adult aquatic insects and riparian predators, such as spiders. These predators are increasingly being used as indicators of aquatic contamination levels. In order to assess the Hg sources being transferred to the terrestrial food web, we measured Hg isotopes in long-jawed spiders (Tetragnathidae), benthic invertebrates (e.g. odonates, hexagenia), and prey fish (e.g., cyprinids) within SLR AOC, spanning from upstream reservoirs to the lower estuary near Duluth, MN and a reference system in the Bad River, WI. Aquatic insect and prey fish δ202Hg values were strongly correlated with spiders (r2 = 0.75), indicating the accumulation of aquatic Hg sources. Depleted δ202Hg values pointed to atmospheric sources in the Bad River and the upper reaches of SLR, whereas progressively enriched δ202Hg indicated increasing industrial sources of Hg in aquatic and riparian food webs in the lower SLR estuary. Our findings indicate that Hg isotope source signatures originating from legacy contamination in the aquatic food web are conserved and transferred into terrestrial food webs. This suggests that Hg isotopes can be used to trace Hg sources in these linked systems and may be useful for assessing recovery from Hg contamination at local scales following remediation.
URLs/Downloads:
DOI: Transfer of legacy mercury from aquatic habitats to the terrestrial food web surrounding the St Louis River