Project Account Number: R/WF-37-06
PRINCIPAL INVESTIGATOR: Robert J. Hudson
INITIATION DATE: March 1, 2006
COMPLETION DATE: February 29, 2008
AFFILIATION: University of Illinois at Urbana-Champaign

Robert J. Hudson
University of Illinois
W-503 Turner Hall, MC-047
1102 S.Goodwin
Urbana, IL 61801
Phone: 217-333-7641
rjhudson@illinois.edu

Thiourea catalysis of MeHg ligand exchange between natural dissolved organic matter and a thiol-functionalized resin: a novel method of matrix removal and MeHg preconcentration for ultratrace Hg speciation analysis in freshwaters
(Analytical and Bioanalytical Chemistry (2007) 388:341-352)
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Objectives
Using state-of-the-art methods in Hg speciation analysis, microbial community analysis, and geospatial modeling, we propose to:

1. Assess the biogeochemical factors that determine MeHg levels in wetland sediments across the landscape.

2. Measure the partitioning of MeHg between porewater and sediments in wetlands across the landscape.
3. Assess the MeHg levels in fish from wetlands with permanent open water.

Methodology
The proposed study involves conducting a large-scale field investigation of MeHg biogeochemistry across the Southern Lake Michigan watershed. The project will involve 3 main tasks. They are:

1. Analysis of microbial molecular markers in previously sampled and analyzed sediments from the Grand Calumet watershed.
2. A spatial survey of MeHg in sediments, water and FISH of 60 wetlands in the Southern Lake Michigan watershed.
3. A temporal study of 10 wetlands across the Southern Lake Michigan watershed.

These studies will employ state-of-the-art methods for analyzing MeHg as well as molecular markers of microbial community composition. Conventional geochemical parameters will also be measured as necessary.

Rationale
Managing the effects of Hg pollution in watersheds depends on knowing the distribution of locations with problematic levels of MeHg and being able to quantify (model) the relationship of loads of Hg and levels of in place contaminants to levels of ambient MeHg in sediments, water, and aquatic biota. At the landscape scale, it is well established that wetlands can be major sources of MeHg to streams and lakes. The proposed measurements will investigate the main hydrological, geochemical, and ecological factors at the landscape scale that govern MeHg levels within wetlands.

Our goal is to characterize and explain the spatio-temporal variations in MeHg concentrations and sediment-porewater partitioning in surficial sediments of wetlands located along the southern shore of Lake Michigan. Since MeHg concentrations are controlled by the balance between Hg methylation and MeHg demethylation, we will test the ability of simple process-based models that incorporate the various geochemical and microbial variables to explain observed MeHg concentrations. Hypotheses regarding the roles of i) sulfide, ii) solid phase S species, iii) pH, iv) SO₄^2-, v) microbial community characteristics, vi) relative abundance of dsr and mer genes, and vi) total Hg burden will be tested. For MeHg partitioning, effects of i) sulfide, ii) solid phase S species, iii) pH, and iv) organic content will be investigated using semi-empirical modeling approaches that incorporate equilibrium speciation modeling.