7/1/2004 - 6/30/2006
- David Armstrong, UW-Madison
- Christopher Babiarz, UW-Madison
Our goal is to characterize the dominant chemical forms of inorganic mercury, Hg(II), and methylmercury (MeHg) in groundwater along a well-characterized ground water flow path and to relate speciation to the factors and processes controlling the transport, methylation, and bioavailability of mercury in groundwater. Our research will be conducted at the USGS WEBB site at the Allequash Creek Watershed in northern Wisconsin. The approach will involve sampling at four flow regimes along instrumented and characterized flow paths: local groundwater, soil lysimeter, intermediate groundwater, and the hyporheic zone. Four major groups of Hg(II) and MeHg species will be investigated: (1) Weakly bound Hg(II) and MeHg (Chelex-100 cation exchange resin); (2) Dissolved natural organic matter-associated species (DEAE anion exchange resin); (3) Colloidal Fe-associated species (ultrafiltration); and (4) inorganic sulfide-associated species (chemical analysis and chemical modeling). We expect the results to fill important gaps in our understanding of the role of Hg speciation in controlling Hg transport to zones of methylation, the bioavailability of Hg(II) to methylating bacteria, and the bioavailability of MeHg for uptake into aquatic food webs.