Paper No. JAWR-07-0058-P of the Journal of the American Water Resources Association (JAWRA). Discussions are open until February 1, 2009.
Long-Term Water Quality and Biological Responses to Multiple Best Management Practices in Rock Creek, Idaho1
Article first published online: 8 JUL 2008
© 2008 American Water Resources Association. No claim to original U.S. government works
JAWRA Journal of the American Water Resources Association
Volume 44, Issue 5, pages 1248–1269, October 2008
How to Cite
Maret, T. R., MacCoy, D. E. and Carlisle, D. M. (2008), Long-Term Water Quality and Biological Responses to Multiple Best Management Practices in Rock Creek, Idaho. JAWRA Journal of the American Water Resources Association, 44: 1248–1269. doi: 10.1111/j.1752-1688.2008.00221.x
- Issue published online: 8 OCT 2008
- Article first published online: 8 JUL 2008
- Received May 7, 2007; accepted December 19, 2007.
- nonpoint source pollution;
- long-term monitoring;
- water quality;
- nitrate loading;
- phosphorus loading;
- sediment loading;
- New Zealand mudsnail;
Abstract: Water quality and macroinvertebrate assemblage data from 1981 to 2005 were assessed to evaluate the water quality and biological responses of a western trout stream to the implementation of multiple best management practices (BMPs) on irrigated cropland. Data from Rock Creek near Twin Falls, Idaho, a long-term monitoring site, were assembled from state and federal sources to provide the evaluation. Seasonal loads of the nonpoint source pollutants suspended sediment (SS), total phosphorus (TP), and nitrate-nitrite (NN) were estimated using a regression model with time-series streamflow data and constituent concentrations. Trends in the macroinvertebrate assemblages were evaluated using a number of biological metrics and nonmetric multidimensional scaling ordination. Regression analysis found significant annual decreases in TP and SS flow-adjusted concentrations during the BMP implementation period from 1983 to 1990 of about 7 and 10%, respectively. These results are coincident with the implementation of multiple BMPs on about 75% of the irrigated cropland in the watershed. Macroinvertebrate assemblages during this time also responded with a change in taxa composition resulting in improved biotic index scores. Taxon specific TP and SS optima, empirically derived from a large national dataset, predicted a decrease in SS concentrations of about 37% (52 to 33 mg/l) and a decrease in TP concentrations of about 50% (0.20 to 0.10 mg/l) from 1981 to 1987. Decreasing trends in TP, SS, and NN pollutant loads were primarily the result of naturally low streamflow conditions during the BMP post-implementation period from 1993 to 2005. Trends in macroinvertebrate responses during 1993 to 2005 were confounded by the introduction of the New Zealand mudsnail (Potamopyrgus antipodarum), which approached densities of 100,000 per m2 in riffle habitat. The occurrence of this invasive species appears to have caused a major shift in composition and function of the macroinvertebrate assemblages.