HR: 0800h
AN: H51B-1127    [Abstracts]
TI: Hyporheic Processes Regulating Trace Element Cycling Under Differing Hydrologic and Biogeochemical Regimes
AU: * Kerr, S
EM: sckerr@wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park Street, Madison, WI 53706
AU: Overdier, J
EM: overdier@facstaff.wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park Street, Madison, WI 53706
AU: Shafer, M
EM: mmshafer@facstaff.wisc.edu
AF: Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 660 N. Park Street, Madison, WI 53706
AB: The overall goal of our research is to improve our understanding of processes responsible for regulating trace metal and DOC cycling in the ground water - stream interfacial region. The hyporheic zone is a dynamic interface region likely to be important in determining metal speciation and fluxes, yet few studies have characterized this zone with respect to trace elements. The area under investigation, a stream catchment in the Northern Temperate Lakes Region of north-central Wisconsin, encompasses contrasting sampling sites with regards to redox and ground water recharge. A hyporheic sampler, specifically designed for low-level trace metal sampling, was used to sample depths of 2, 5, 7, 10, and 15 cm below the sediment-water interface at two locations in the watershed, one characterized by downwelling conditions with oxic streamwater, and the other upwelling with anoxic groundwater. The strength of the upwelling regime varies seasonally, becoming dominant during the late spring and summer but weakening during the fall and winter. Results show that hyporheic sulfide levels during summer 2004 were twice as high at the upwelling, anoxic site than at the downwelling, oxic site. Higher sulfide levels were seen in early (mid-June) versus mid summer (late July) at both sites. Sulfide levels decreased with depth in early summer but increased with depth in mid summer at the upwelling site while the opposite trend was observed at the downwelling site. The downwelling site exhibits higher DOC levels (driven by DOC-rich stream water) than the upwelling (ground water dominated) site and values increased with depth for the former while they decreased with depth for the latter site. Both sites saw an initial increase in DOC from spring to summer, but levels at the downwelling site decreased in mid summer (in concert with stream DOC levels) while levels at the upwelling site continued to increase. Levels of Zn were higher than Cu at both sites. There was little difference in Cu levels between sites while Zn levels were higher at the downwelling site. Iron was also higher at the downwelling site ranging from 77-190 micromolar and increasing with depth while at the upwelling site levels ranged from 30-77 micromolar and decreased with depth. Voltametric data (ASV) addressing the quantity and strength of metal-binding ligands is being synthesized to aid our interpretation of processes impacting metal levels and speciation.
DE: 4805 Biogeochemical cycles (1615)
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1065 Trace elements (3670)
DE: 1615 Biogeochemical processes (4805)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting