U.S. Geological Survey Water-Quality Assessment of the Trinity River Basin, Texas Nutrients in Streams Draining an Agricultural and an Urban Area, 1993-95 u

Water samples collected from streams draining an agricultural area in the west-central part of the Trinity River Basin upstream from the Richland-Chambers Reservoir and from streams draining an urban area in the Dallas-Fort Worth metropolitan area during March 1993 September 1995 were analyzed for nutrients (nitrogen and phosphorus com-pounds). A comparison of the data for agricultural and urban streams shows the maximum concentration of total nitrogen is from an urban stream and the maximum concentration of total phosphorus is from an agricultural stream. One-half of the samples have total nitrogen concentra-tions equal to or less than 1.1 and 1.0 mil-ligrams per liter in the agricultural and urban streams, respectively; and one-half of the samples have total phosphorous concentrations equal to or less than 0.04 and 0.05 milligram per liter in the agri-cultural and urban streams, respectively. The highest concentrations of total nitro-gen in both types of streams are in the spring. The minimum concentrations of total nitrogen are during the summer in the agricultural streams and during the winter in the urban streams. Concentra-tions of total phosphorus in agricultural streams show negligible seasonal vari-ability. The highest concentrations of total phosphorus are in spring and possi-bly late summer in the urban streams. In the midrange ofstreamfiow in the urban streams and throughout the range of streamfiow in the agricultural streams, concentrations of total nitrogen increase. Concentrations of total phosphorus increase with streamflow in the middle and upper ranges ofstreamfiow in both agricultural and urban streams