HR: 17:24h
AN: H44B-08    [Abstracts]
TI: Trace Metal Cycling Within the Riparian Wetland and Hyporheic Zones of a Northern Temperate Stream Catchment
AU: * Shafer, M M
EM: mmshafer@wisc.edu
AF: University of Wisconsin-Madison, Environmental Chemistry & Technology, 660 North Park Street, Madison, WI 53706 United States
AU: Kerr, S
EM: sckerr@students.wisc.edu
AF: University of Wisconsin-Madison, Environmental Chemistry & Technology, 660 North Park Street, Madison, WI 53706 United States
AU: Overdier, J
EM: overdier@facstaff.wisc.edu
AF: University of Wisconsin-Madison, Environmental Chemistry & Technology, 660 North Park Street, Madison, WI 53706 United States
AU: Armstrong, D
EM: armstron@engr.wisc.edu
AF: University of Wisconsin-Madison, Environmental Chemistry & Technology, 660 North Park Street, Madison, WI 53706 United States
AB: Our study addresses watershed linkages to streams and lakes, focusing on trace element cycles and metal-binding ligand production and transport. The research is being carried out at an extensively instrumented stream catchment in the Northern Temperate Lakes Region of north-central Wisconsin - a system that is also under investigation by the NSF-funded Long Term Ecosystem Research (LTER) program and the USGS Water Energy and Biogeochemical Budgets (WEBB) program. Within the study system we have identified flow paths of contrasting redox, in addition to zones of positive and negative ground water recharge. Detailed temporal data sets of water and ligand chemistry data are being obtained from dense networks of nested piezometers and hyporheic samplers placed in these contrasting regions/flow paths. In addition to major element chemistry, data on over 25 trace metals are acquired using high-resolution ICP-MS. A suite of oxyanionic metals is included to assist in our interpretation of DOC and iron oxide/sulfide partitioning mechanisms. Along a predominantly oxic flow path from regional ground water to stream riparian porewaters, concentrations of both Mn and Zn drop markedly (10-100 fold). Arsenic is also lost to riparian and wetland sediments. In contrast, levels of Cu increase 2-3 fold from upland hillslope groundwater to stream riparian porewaters. The importance of sulfide and iron in regulating ground water fluxes of certain trace metals to the stream is evident when oxic and anoxic flow paths are compared. Levels of Cu in many anoxic regions (0.06 nM Cu, 50-700 nM sulfide, 30-40,000 nM Fe) are strikingly reduced from that observed in oxic zones (4-6 nM, Cu, $<$20 nM sulfide, 100 nM Fe). Studies are in progress to characterize the oxidation state of Cu in the contrasting micro-environments. Concentrations of both Zn and Tl are significantly lower (10 fold) along anoxic flow-paths than in oxic regions. Large seasonal variations in Pb levels are observed, with particularly elevated concentrations seen in spring, coinciding with greater DOC fluxes. Temporal variations in metal levels and fluxes, as driven by seasonality in hydrologic-forcing, will be emphasized in the paper.
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