ZEBRA MUSSELS ACCUMULATE AND CONCENTRATE MERCURY IN A EUTROPHIC LAKE

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.

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

Authors:

Sarah Janssen, US Geological Survey  (sjanssen@usgs.gov)

Tylor Rosera, US Geological Survey  (trosera@usgs.gov)

Jacob Ogorek, US Geological Survey  (jmogorek@usgs.gov)

Joseph Noeske, University of Wisconsin- Madison  (jnoeske@wisc.edu)

Katherine McMahon, University of Wisconsin- Madison  (katherine.mcmahon@wisc.edu)