Project Number:
WR07R008
Funding Year:
2007
Contract Period:
7/1/2007 - 6/30/2009
Funding Source:
UWS
Investigator(s):
PIs:- Martin M. Shafer, UW-Madison, Dept. of Civil and Environmental Engineering
- Christopher L. Babiarz, UW-Madison, Dept. of Civil and Environmental Engineering
- David E. Armstron, UW-Madison, Dept. of Civil and Environmental Engineering
- Eric E. Roden, UW-Madison, Dept. of Geoscience
Abstract:
Background/Need: This project addressed the groundwater-related problem of methylmercury (MeHg) formation in hyporheic zones, the subsurface regions of stream- and lake beds where the active exchange of surface and groundwater occurs. MeHg formation involves the methylation of Hg(II), in the hyporheic zone, by bacteria. Subsequent transport of the MeHg into surface waters leads to accumulation of this
highly toxic substance in aquatic food webs.
Objectives: Our research was focused on determining the main factors controlling the bioavailability of inorganic Hg(II) for production of MeHg in wetland hyporheic zones. Our objectives included:
- Experimentally determining rates of mercury methylation and demethylation using isotopic tracer techniques.
- Determining whether observed MeHg concentrations were allochthonous or produced in situ.
- Assessing the influence of strong Hg-binding ligands on methylation rate potential and determining whether sulfide or dissolved organic carbon (DOC) played the greatest role in regulating Hg(II) bioavailability (as probed by methylation rate potential measurements) to methylating bacteria.
- Determining whether neutral complexes of mercury and sulfide, such as HgS0, are the most bioavailable form of Hg(II) to bacteria.
- Comparing two geochemically different sites within the wetland, with different groundwater flow patterns, to determine if Hg(II) bioavailability and methylation were influenced by the contrasting redox conditions.