HR: 0800h
AN: H51B-0453    [Abstracts]
TI: In-Stream Nitrate Immobilization Across Development Gradients and Stream Network Position in a Rapidly Developing Mountain Watershed, West Fork of the Gallatin River, Big Sky, Montana.
AU: * McNamara, R A
EM: rebecca.mcnamara@myportal.montana.edu
AF: Watershed Hydrology Group Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: McGlynn, B L
EM: bmcglynn@montana.edu
AF: Watershed Hydrology Group Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: Gardner, K K
EM: kristin.k.gardner@gmail.com
AF: Watershed Hydrology Group Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AU: Jenkins, P
EM: pjenkins.montana@gmail.com
AF: Watershed Hydrology Group Department of Land Resources and Environmental Sciences Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717, United States
AB: Nitrogen immobilization in streams is an important process and partially determines the balance between N removal and N export from headwater catchments. In-stream immobilization of streamwater N is well-studied, yet poorly understood, especially as one moves from reach to stream network scales, and across morphologic or ground water- surface water exchange gradients, seasons, and ranges of ambient N concentrations. Our goal was to quantify the range of in-stream NO₃^- immobilization rates across the stream network by comparing low and elevated ambient NO₃^- streams and to assess the role of the stream network in modifying observed watershed N loading patterns and export dynamics. We focused on the 200 km² rapidly developing montane watershed of the West Fork of the Gallatin River, Big Sky. This site provides an ideal natural laboratory for analysis of landuse change impacts on water quality because of its montane ecosystem, accelerated land development, and adjacent wilderness. We conducted 31 stream tracer tests (15 steady-state and 16 slug additions) across eight, 400-1250m stream reaches, with a range of ambient NO₃^- concentrations (<0.01-2.17 mg/l) and watershed size (0.408-85 km²). Each of the eight streams was paired for comparison based on similar watershed area and total discharge; each pair included a stream of high and low ambient NO₃^-, reflecting varying degrees of exurban development and upland wastewater disposal. Quarterly assessments of montane in-stream N immobilization were also conducted to assess seasonality. For each stream addition, we tracked a concurrent conservative (NaCl) and non-conservative (KNO₃) tracer with synoptic and breakthrough curve sampling. We further characterized gross and net streamflow gains/losses over each reach with mass recovery methods. This work represents a first step toward integrating watershed and stream network biogeochemistry in a rapidly developing mountain watershed.
DE: 0469 Nitrogen cycling
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2007 Fall Meeting