HR: 1340h
AN: H53D-1451    [Abstracts]
TI: Potentially Non-Reversible Changes in Biogeochemical Cycling of an Alpine Wetland in Responses to Changes in Climate, Green Lakes Valley, Colorado
AU: * Nielson, A
EM: ashley.nielson@colorado.edu
AF: Institute of Arctic and Alpine Research University of Colorado, INSTAAR, CB 450 University of Colorado, Boulder, CO 80300, United States
AU: Williams, M
EM: markw@snobear.colorado.edu
AF: Institute of Arctic and Alpine Research University of Colorado, INSTAAR, CB 450 University of Colorado, Boulder, CO 80300, United States
AU: Toetz, D
EM: dale.toetz@okstate.edu
AF: Oklahoma State University, 430 Life Science West, Stillwater, OK 74078, United States
AU: Caine, N
EM: cainen@spot.colorado.edu
AF: Institute of Arctic and Alpine Research University of Colorado, INSTAAR, CB 450 University of Colorado, Boulder, CO 80300, United States
AB: Alpine wetlands have been shown to be among the most sensitive types of wetlands to changes in climate. Yet, little is known about the hydrology of alpine wetlands and how the biogeochemical cycling of these wetlands may respond to changes in climate. Here we report on the results of surface and subsurface water samples collected weekly from May to October from 2003-2007, from a 2-ha wetland located at an elevation of 3593m in Green Lakes Valley (GLV). These results are compared to historical samples collected from 1986-1990. GLV is within the city of Boulder Watershed and part of the Niwot Ridge LTER. Mean annual air temperatures were about +1C higher in the 2000's compared to the late 1980's. Samples were analyzed for all major solutes, dissolved organic carbon (DOC), and stable water isotopes. Geochemical weathering products during baseflow (e.g. Ca⁺⁺, Mg⁺⁺, Na⁺, SO₄^-)are ten times higher since the late-1980's, with little change during June and July. Nitrate concentrations during baseflow have also doubled over the same time period. For 2003-2007, nitrate was retained by the wetland with retention as much as 99% during baseflow. In contrast, DOC is produced within the wetland, and concentrations in the outflow ( ~ 1.0 mg/L) generally higher than the inflow ( ~ 0.5 mg/L). DOC concentrations in subsurface wells were an order of magnitude greater than in surface waters, suggesting that biogeochemical cycling played an important role in the retention and transformation of the chemistry of inflowing waters before export to down gradient ecosystems. We evaluated potential hydrologic controls by determining the relationships between water chemistry, outlet discharge, residence time, source waters, and flow paths of the wetland. Outflow discharge peaked at 8.0 L/s on June 17 consistent with a snowmelt-dominated source waters. However, results from a constant injection LiBr tracer yielded a residence time of ¬ ~ 35 hours, suggesting a significant amount of hydrologic storage within the wetland. Seasonal Δ18O values range from -20 ‰ to -9 ‰, suggesting changing source waters and flow paths. We will use end member mixing analysis (EMMA) and mixing models parameterized with stable isotopes and biogeochemical tracers to evaluate changing source waters and flow paths during years 2003 to 2007. Changes in climate may in turn have caused changes in the hydrology that have resulted in potential irreversible effects on the biogeochemical cycling of this alpine wetland.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
DE: 1890 Wetlands (0497)
SC: Hydrology [H]
MN: 2007 Fall Meeting