Wisconsin's Role in Great Lakes Restoration - American Water ...

7. Influence of Regional Mercury Sources on Lake Michigan Tributaries: 15-Year
Comparison
Christopher Babiarz, Environmental Chemistry and Technology Program,
University of Wisconsin, Madison, WI, cbabiarz@wisc.edu
Fifteen years have passed since the inception of the Lake Michigan Mass Balance Study
(LMMB), and during that period both industrial use and atmospheric emissions of mercury
(Hg) have been reduced. Given these reductions, and new information on the residence time
of Hg in aquatic ecosystems, we have begun an abridged version of the tributary monitoring
project to provide an interim benchmark before new caps on mercury emissions are
completely met.
Our past work has shown that flow rate strongly influences the concentration of total mercury
(HgT), methylmercury (MeHg), and suspended particulate matter (SPM), in rivers. Because
the relative speciation of mercury also varies with flow rate the project focuses on three
distinct flow regimes: base flow, storm events, and the spring melt. Measurements of HgT and
MeHg concentration in the unfiltered and filtered phases, and important ancillary chemistry
(DOC, pH, specific conductivity, and temperature) are being quantified.
By establishing the current condition of these tributaries, the project provides two important
outcomes: (a) the data will be an important longitudinal benchmark to assess the impact of
recent and future emissions reductions, and (b) the premise that tributaries can be used as
sentinels will be tested by comparing the current data to those collected during the LMMB. By
laying this groundwork, we hope to quantify the regional impact of current Hg emission rules
and provide a scientific basis for future decisions about implementing additional control
programs in the region.
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