To manage nutrient loads in rivers, point and nonpoint sources of loads need to be quantified. Point-source loads can be estimated using data from wastewater-treatment plants and then compared to instrearn loads measured at water-quality-monitoring sites. As part of the National Water-Quality Assessment (NAWQA) Program, data were collected during 1994 in an effort to improve estimates of nutrient loads in the South Platte River Basin.
Effluent nutrient data for 1993 were compiled from 30 wastewater-treatment plants in the basin. Ammonia routinely was measured at 96 percent of the plants, nitrite plus nitrate at 27 percent, and organic nitrogen at 11 percent. Total phosphorus routinely was measured at 19 percent of the plants and orthophosphate at 4 percent. Methods were developed for estimating nutrient loads for each nutrient species, and nutrient loads were estimated for each treatment plant.
During April 1994, samples were collected at 60 surface-water sites in the basin to determine nutrient species concentrations and to calculate instantaneous nutrient loads. Total nitrogen loads in the South Platte River ranged from 84 pounds per day (lb/d) to 18,000 lb/d; total phosphorus loads ranged from 10 to 3,200 lb/d. Highest loads were related to wastewater-treatment-plant discharges and agricultural land use. Loads decreased downstream from point sources due to diversion of water and instream processes.
1 U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO 80225
2 Colorado State University, Ft. Collins, CO 80526