Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2003
Publication Date: 7/3/2003
Citation: Haggard, B.E., Moore Jr, P.A., Chaubey, I., Stanley, E.H. 2003. Nitrogen and phosphorus concentrations and export from an ozark plateau catchment in the United States. Biosystems Engineering. 86(1):75-85. Interpretive Summary: Nitrogen and phosphorus concentrations were measured in four watersheds of Beaver Lake, an impoundment on the White River in the Ozark Plateaus of Arkansas, to assess possible relationships between pasture land use and the amount and transport of nitrogen and phosphorus in streams. Nitrogen and phosphorus concentrations were measured at ten sites within the four watersheds, approximately 17 times per year. The amount of nitrogen and phosphorus transported through was calculated using a relationship between streamflow and concentration. Stream nitrogen and phosphorus concentrations and the amount of these nutrients being transported by the stream increased with the fraction of pasture land use within each smaller watershed. The amount of nutrients transported also increased with the total surface area of the watersheds, but the amount of nutrients transported per unit area of the watershed decreased with watershed size. The amount of nutrients transported in the streams of the Beaver Lake watershed is 3 to 10 times greater than streams representing undeveloped areas throughout the United States by the U.S. Geological Survey Hydrologic Benchmark Network. It appears that pasture land use increases not only nutrient concentrations in the streams but also the transport of nutrient in the streams to Beaver Lake.
Technical Abstract: Nitrogen and phosphorus concentrations were measured in four sub-watersheds of Beaver Lake, a reservoir on the White River in the Ozark Plateaus of Arkansas, to assess possible relationships between pasture land use and stream nutrient concentrations and export. Surface water samples were collected 17 times annually for two years from ten total stream sites within the four watersheds. Samples were analyzed for soluble reactive phosphorus (SRP), total phosphorus (TP), and ammonium-N, nitrate-N, total Keldjhal nitrogen (TKN) and total nitrogen (TN). Discharge was measured at four gaged stream stations, and nutrient export was calculated using the U.S. Geological Survey ESTIMATOR software and non-biased re-transformation from log space. Stream SRP, nitrate-N and TN concentrations (geometric mean) increased linearly with percent of pasture in watersheds, whereas nitrogen and phosphorus export coefficients increased exponentially with pasture land use. Nitrogen and phosphorus export (kg per yr) increased with basin size, but nutrient yield (kg per square km per yr) decreased with basin size. Nutrient yield was from 3 times to over 10 times greater than nutrient yields observed in regional undeveloped streams and the average of the Hydrologic Benchmark Network of the U.S. Geological Survey. It is apparent that pasture land use in this basin affects not only absolute stream nutrient concentrations but also the export of nutrients to receiving the aquatic ecosystems, Beaver Lake and its tributaries.