HR: 0800h
AN: H51B-0450    [Abstracts]
TI: Spatio-Temporal Controls of Stream Water Nitrogen Export in a Rapidly Developing Watershed in the Northern Rockies
AU: * Gardner, K K
EM: kristin.k.gardner@gmail.com
AF: Watershed Hydrology Group Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59716,
AU: McGlynn, B L
EM: bmcglynn@montana.edu
AF: Watershed Hydrology Group Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59716,
AB: Human alteration of the patterns of land use/land cover (LULC) on the earths surface is one of the most profound impacts on the functioning of natural ecosystems. At the watershed scale, we expect that not only the amount and type of landscape alteration, but also its spatial distribution and the corresponding watershed characteristics, hydrologic conditions, and biological season will dictate the spatio-temporal patterns of streamwater nitrogen (N). We conducted six synoptic sampling events (50 sites) and weekly streamwater sampling (7 sites) in the West Fork Watershed, a 212 km² mountainous watershed in Southwestern Montana, which drains the rapidly developing Big Sky resort community. Synoptic sampling campaigns captured each season and a range of hydrological conditions and biologic activity. Samples were analyzed for inorganic and organic forms of nitrogen. We performed exploratory multiple regression analysis to determine the explanatory variables for spatio-temporal streamwater nitrogen (N) patterns. Variables considered included DEM derived hydrologic features (e.g. stream order, upland travel time, slope, aspect, riparian area, riparian buffer ratios, and watershed area), geology, forest cover, and septic locations. These variables were used in generalized least squares with a spatial correlation model based on weighted stream distance to predict streamwater nitrate concentrations. We found greatest correlation (adj r² =0.90) in the winter with variables including number of septic locations, upland fertilization, and geology. This suggests nitrogen loading to the watershed was more conservatively transported through the uplands and stream network in the winter. In the late summer, however, transport and related biological variables became more important, and included travel time weighted septic loading locations, riparian hillslope buffer ratios, and stream order (adj. r² =0.21). Here, we present the results of our exploratory statistical analysis as a first step toward modeling the impact of watershed location and spatial distribution of LULC change on the spatial, seasonal, and speciation patterns of streamwater N.
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1847 Modeling
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2007 Fall Meeting