Mercury Concentrations and Methylation Rate Potentials in Lake Mendota, Wisconsin, USA: 2020-2021

This dataset describes mercury (Hg) concentrations and methylation rate potentials that were measured in Lake Mendota, Wisconsin, US in 2020 and 2021. This work is a collaboration between the University of Wisconsin, University of California-Davis, and the U.S. Geological Survey. Samples were collected to examine the linkages between Hg methylation, biogeochemical conditions, and microbial community abundance during lake stratification (September and October). Samples were collected at depths ranging from 0-23 meters, exact values vary per sampling event and are detailed in the corresponding tables. Total Hg (THg) concentrations increased with depth across the anoxic hypolimnion and slightly increased from September to October but exhibited comparable concentrations between both sampling years. Filter-passing MeHg increased with depth across all four sampling dates. Across all incubations, the formation of MeHg under ambient conditions, quantified using a 198Hg(II) tracer, varied widely based on incubation depth and subsequent redox state and the methylation rate potential (Kmet) ranged from 0.001 day-1 to 0.165 day-1. Demethylation rates (Kdem) were quantified using a Me204Hg tracer. The filtered control incubations showed increasing Kdem values with increasing sulfide, leveling off to approximately 0.2 day-1. Concentration and methylation rate potential data were compared to metagenomics and transcripnomics measurements conducted by the University of Wisconsin and further detailed in the corresponding journal article (Peterson et al. 2025, DOI:10.1021/acs.est.4c12759).