Monday, November 13, 2006 - 11:45 AM

Mitigation of Pesticide Runoff from a Commercial Nursery.

Jay Gan1, Wenjian Lao1, Leo Walsh1, Christopher Martinez2, Darren Haver2, John Kabashima2, and Laosheng Wu1. (1) Dept of Environmental Sciences, Univ of California, Riverside, CA 92521, (2) Cooperative Extension Orange County, Univ of California, Irvine, CA 92618

Pesticides in nursery runoff are an important contamination source for surface streams and estuaries in urban regions such as Southern California. Implementation of water quality protection regulations (e.g., TMDL) mandates that mitigation practices be developed to curtail such nonpoint sources. In this study, we developed methods for measuring runoff flow rates under dry weather conditions and during storm events at a large commercial nursery (200 acres) located in Orange County, CA. Runoff samples were analyzed for a suite of pesticides on a weekly basis, and before and after the use of various management practices to evaluate the efficiency of the mitigation practices. The majority of runoff discharge was contributed by storm runoff, which was about 10 times of the total volume recorded during the dry weather months. Of the pesticides detected, synthetic pyrethroids including bifenthrin, fenpropathrin, cyhalothrin, cyfluthrin and deltamethrin were frequently found, while bifenthrin was also present.  The total bifenthrin export in the storm runoff was over 95% of the total runoff for the entire monitoring period, suggesting that management of storm runoff is essential for reducing pesticide runoff. Mitigation practices such as construction of retention basins and check-dams reduced about 34% of runoff volume and over 92% of bifenthrin loads under dry weather conditions. The reduction was attributed to pesticide-laden suspended solids, and in-situ biodegradation in the retention basins. To further reduce pesticide runoff, retention of the “first flush” of the first few rain storms in the season will be critical.