Land Use and Groundwater Quality in Western Montana: The Impact on Nutrient Budgets for Surface Waters

摘要

Two springbrooks and their source aquifers in the Flathead River basin of northwestern Montana were studied to determine the mass transport of phosphorus and nitrogen from the groundwater systems into surface waters. The Spring Creek system, which erupts from the fluvial aquifer near the Flathead River upstream from Flathead Lake, transported an average concentration of 7.5-14.3 micrograms/1-TP and 0.6-0.9 micrograms/1-NO3-N upon discharge into the Stillwater River. The values at the springheads were 6.1-22.1 micrograms/1-TP and 0.9-1.04 micrograms/1-NO3-N. Measurements of water table elevations in conjunction with river flow measurements, showed that the flow of Spring Creek was dynamically controlled by the Flathead River. The creek chemistry, however, was subsidized by inputs of nitrogen and phosphorus within the aquifer, probably from fertilizers in agricultural areas and sewage in urban areas. Roy's Creek, a springbrook on the east shore of Flathead Lake, carried .5 to 1.5 times the phosphorus and nitrogen transported by surface runoff.