HR: 0800h
AN: H31B-1302    [Abstracts]
TI: Sensitivity of simulated stream water N and P concentrations and N:P ratios to precipitation regimes in a central Minnesota watershed
AU: * Green, M B
EM: mgreen@umn.edu
AF: University of Minnesota - Graduate Program of Water Resources Science, 1991 Upper Buford Circle, Saint Paul, MN 55108 United States
AU: Wang, D
EM: wangd@umn.edu
AF: University of Minnesota - Department of Soil, Water, and Climate, 1991 Upper Buford Circle, Saint Paul, MN 55108 United States
AU: Murphy, M
EM: murp0430@umn.edu
AF: University of Minnesota - Department of Geology and Geophysics, 310 Pillsbury Drive SE, Minneapolis, MN 55455 United States
AU: Almendinger, J E
EM: dinger@smm.org
AF: Science Museum of Minnesota - St. Croix Watershed Research Station, 16910 152nd St. North, Marine on St. Croix, MN 55047 United States
AB: This work addresses the impact that precipitation regimes (annual mean, frequency, and intensity) have on stream water nitrogen (N) and phosphorus (P) concentrations and N:P ratios in a minimally-impacted watershed. We hypothesized that low frequency (LF) and high intensity (HI) precipitation regimes would result in low stream water N:P ratios compared to regimes with high frequency (HF) and low intensity (LI) regimes. The hypothesis was based on the secondary hypothesis that LF/HI regimes would generate more overland runoff relative to baseflow, thus transporting more P to the stream relative to N. Hydrology and water quality in the Lower Tamarack River watershed in central Minnesota was simulated using the Soil and Water Assessment Tool (SWAT). The analysis examined the sensitivity of stream water N and P concentrations and N:P ratios to parameters in the precipitation generation algorithm. The results showed that baseflow comprised a lower percentage of stream flow in LF/HI precipitation regimes compared to HF/LI regimes. Stream water total N (TN) concentrations were lower and the total P (TP) concentrations were higher in LF/HI precipitation regimes compared to HF/LI regimes. These differences in turn resulted in lower TN:TP ratios in LF/HI precipitation regimes and higher TN:TP ratios in HF/LI precipitation regimes. The results suggest that the nutrient status in the Lower Tamarack River could change from P limitation (TN:TP > 50) to possible N limitation (TN:TP < 10) given a significant alteration of the precipitation regime. Our results have broad regional significance by suggesting that precipitation regime and watershed hydrology are important mechanisms in controlling stream-water N:P ratios, which may help explain why streams in arid and semi-arid climates commonly have lower stream-water N:P ratios than streams in mesic climates.
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1813 Eco-hydrology
DE: 1845 Limnology (0458, 4239, 4942)
DE: 1871 Surface water quality
DE: 1879 Watershed
SC: Hydrology [H]
MN: Fall Meeting 2005