Mercury is a ubiquitous pollutant that can result in the contamination of aquatic food webs and is a leading cause for fish consumption advisories worldwide. Once in aquatic ecosystems, mercury enters a complex biogeochemical cycle that includes ligand complexation, photo-chemistry, and microbial transformations. These processes culminate with the formation of toxic methylmercury by microorganisms, which is the key step leading to bioaccumulation and biomagnification of mercury in the food web. The balance between these transformation processes thus determines the extent of mercury uptake into the food web, evasion back to the atmosphere, or burial in sediments. These processes are dictated by an array of biogeochemical factors such as organic matter composition and concentration, redox conditions, water quality, and microbial community activity. While we expect to see declines in mercury releases to the environment in the coming years, other local and global changes, such as eutrophication, climate change, and biological invasions, are also expected to alter these biogeochemical cycles and subsequent biological mercury burdens. Emerging tools in the field, such as stable isotopes and microbial metagenomics, have improved our ability to understand the biogeochemical mechanisms underlying mercury transformation, which is critical to modeling and predicting changes in mercury cycling in response to global and regional change. For this session , we invite abstracts that focus on identifying specific biogeochemical drivers of mercury transformation in aquatic ecosystems including chemical and microbial studies as well as modeling approaches. Specific emphasis will be placed on presentations that use interdisciplinary approaches, emerging techniques, and investigate how local or global changes are influencing the mercury cycle.

Lead Organizer: Benjamin Peterson, University of Wisconsin Madison (bpeterson26@wisc.edu)

Co-organizers:

Sarah Janssen, U.S. Geological Survey - Mercury Research Laboratory (sjanssen@usgs.gov)

Presentations

05:30 PM

ZEBRA MUSSELS ACCUMULATE AND CONCENTRATE MERCURY IN A EUTROPHIC LAKE (8074)

Primary Presenter: Nicholas Scheel, University of Wisconsin- Madison (nscheel@wisc.edu)

Mercury (Hg) is a toxic heavy metal that is released into the environment due to anthropogenic activity. When it enters freshwater systems, it can be converted to methylmercury (MeHg) by microorganisms, at which point it bioaccumulates into the food web, posing a risk to wildlife and human health. Hg methylation and bioaccumulation can be dictated by a myriad of co-occurring stressors including changes in food web structure. Zebra mussels are an invasive species in the United States, found in freshwater lakes throughout the midwest, which have been tied to alterations in Hg bioaccumulation. As filter feeders, they remove nutrients and other elements from the water column and shunt them to the benthic zone. We proposed that zebra mussels altered the distribution and cycling of Hg in Lake Mendota by filtering it from the water column and accumulating it in their flesh and/or shunting it to the benthic zone. In Summer 2023, we measured total Hg (THg) and MeHg samples in sediment, zebra mussels, and plants. We found that the concentration of Hg species in zebra mussel varied spatially, with THg in zebra mussel tissue ranging from around 30-50 ng/g and MeHg ranged from 10-30 ng/g. The presence and distribution of mercury within zebra mussels raises questions about how this impacts aquatic food webs and what geochemical factors affect the rate of Hg methylation and bioaccumulation within Lake Mendota.

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