Mercury trends and cycling in northern Wisconsin related to atmospheric and hydrologic processes

Atmospheric deposition is the principal source of mercury to remote northern landscapes, but its fate depends on multiple factors and internal feedbacks. Here we document long-term trends and cycles of mercury in the air, precipitation, surface water and fish of northern Wisconsin that span the past three decades; and we investigate relationships to atmospheric processes and other variables, especially the regional water cycle. Consistent with declining emission inventories, there was evidence of declining trends in these time series; but the time series for Hg in some lakes and most fish were dominated by a near-decadal oscillation that tracked the regional oscillation of water levels. Concentrations of important solutes (SO4, DOC) and the acid-base status of lake water also tracked water levels in ways that cannot be attributed to simple dilution or concentration. The explanatory mechanism is analogous to the â reservoir effectâ wherein littoral sediments are periodically exposed and re-flooded, altering the internal cycles of sulfur, carbon and mercury. These climatically-driven, near-decadal oscillations confound short-term time series and complicate relationships between Hg emissions, deposition and bioaccumulationThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author