Linking precipitation and atmospheric deposition to methylmercury concentration in larval dragonflies

Aquatic ecosystems within the Laurentian Great Lakes region are contaminated with methylmercury (MeHg). Atmospheric deposition of inorganic mercury (Hg) from anthropogenic and recycled sources constitutes the primary input of Hg into aquatic ecosystems, where methylating bacteria convert a fraction to organic MeHg. Aquatic food webs are important pathways for exposure of wildlife and humans to MeHg, a highly toxic compound which biomagnifies in food webs and bioaccumulates in organisms to harmful levels. Burrowing gomphid dragonfly larvae, useful biosentinels, were sampled from 15 lakes across four U.S. National Park units in the Great Lakes region from 2008-2012 and analyzed for MeHg content. Rates of total Hg in wet deposition, sulfate ion concentration, and precipitation depth were used to examine the response of regional dragonfly MeHg concentrations to atmospheric inputs from nearby monitoring stations for the periods 0-12 months prior (yrt-1) and 12-24 months prior (yrt-2) to sampling. A linear mixed-effects model indicated that precipitation depth occurring during yrt-2 was the best predictor of larval dragonfly MeHg concentration, followed by yrt-1 total Hg deposition rate. This study demonstrates use of simple models to identify factors influencing MeHg concentrations in aquatic food webs and to predict future responses to changes in atmospheric loading