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Williamson County, much of which lies within the Harpeth River watershed, is the fastest growing county in the State. Rapid development has raised concern about aquatic environments in this watershed. In response to this concern, the U.S. Geological Survey, in cooperation with the Tennessee Department of Environment and Conservation, conducted a study in the watershed to estimate stream loads of selected nutrients including nitrogen, ammonia, and phosphorus, based on historical water-quality and discharge data collected by both agencies. A comparison of available data indicated that the Harpeth River at Kingston Springs was the only monitoring station in the watershed with adequate existing data. By using these data, constituent loads were estimated using multivariate log-linear regression against three independent variables (discharge, season, and time). Daily constituent loads were computed from the model and summarized to annual loads.
Estimates of mean annual-area based loads (yields) at the monitoring station at Harpeth River at Kingston for the period 1983-95 were 0.06, 1.2, 1.0, and 0.56 tons per square mile for total ammonia, total nitrite plus nitrate, total Kjeldahl nitrogen, and total phosphorus, respectively. Yields are comparable with those for other river basins in the Middle Tennessee area during similar periods. Estimated annual yields of total ammonia and total nitrite plus nitrate for the Harpeth River were near the median for national estimates; however, total phosphorus yields were above the national median.
Upper and lower limits of error were calculated for annual loads for each constituent based on regression statistics. Examination of the distribution of nutrient samples within the streamflow distribution shows that the data sets are biased toward low streamflows. Because the greatest part of loads generally occur during high streamflows, underrepresentation of data for high flows reduces the accuracy of load estimates. A sampling scheme that incorporates sample frequency, seasonality, and variable flow conditions would be valuable in developing more accurate estimates of constituent loads and trends for use in a detailed evaluation of water quality for the Harpeth River.
This abstract can be cited as follows:
Aycock, R.A., 2001, Nutrient loads and long-term trends for nitrogen, ammonia, and phosphorus in the Harpeth River watershed, water years 1983-95 [abs.], in Tennessee Water Resources Symposium, 11th, Burns, Tenn., 2001, Proceedings: Tennessee Section of the American Water Resources Association, p. 2B-27.
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