Humic, terrestrially derived dissolved organic matter is associated with higher methylmercury concentrations in prairie wetland ponds

Dissolved organic matter (DOM) comprises most of the organic matter in the water column of surface waters, playing important roles in biogeochemical cycles, including that of mercury. We characterized DOM in surface water of wetlands ponds located in the prairie pothole region (PPR) of North America using optical techniques, including excitation emission matrices and derived optical indices, and related DOM character to methylmercury concentrations ([MeHg]) in whole water. Water from wetland ponds was collected along dissolved organic carbon and MeHg concentration gradients in Saskatchewan, Canada. Generally, as [MeHg] increased, DOM became terrestrially derived (decreased fluorescence index and biological index), more humic (increased humification index), and more aromatic (increased SUVA 254 ). Our current work demonstrates spatial differences in DOM character among prairie wetland ponds, establishing that differences in DOM composition among ponds may contribute to differences in [MeHg] observed in ponds in the PPR.