Submitted to: National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment
Publication Type: Proceedings
Publication Acceptance Date: October 1, 2008
Publication Date: April 5, 2011
Citation: Lizotte Jr, R.E., Shields Jr, F.D., Knight, S.S., Bryant, C.T. 2011. Pesticide trapping efficiency of a modified backwater wetland using a simulated runoff event. In: Proceedings of the conference "Fifty Years of Soil & Water Research in a Changing Agricultural Environment." National Sedimentation Laboratory, September 2-5, 2008. Oxford, Mississippi. CD-ROM. Interpretive Summary: Natural wetlands occurring in the flood plain near rivers can be modified and used as best management practices to improve and sustain river water quality. A study was done in a modified natural wetland near the Coldwater River in northern Mississippi to improve our understanding of how efficiently this wetland could trap three commonly used agricultural pesticides, atrazine, metolachlor and fipronil. The study showed the wetland was capable of efficiently trapping all three pesticides and preventing them from entering the Coldwater River. These results are of interest to regulatory and other agencies and the pesticide industry as an additional tool to improve and sustain river water quality and overall environmental quality.
Technical Abstract: This study examined the trapping efficiency of a modified backwater wetland amended with a mixture of three pesticides, atrazine, metolachlor, and fipronil, using a simulated runoff event. The 700 m long, 25 m wide wetland, located along the Coldwater River in Tunica County, Mississippi, was modified for hydrologic control by adding weirs at both ends. Pesticide mixture was injected into the wetland at the upstream weir simulating a one-hour 1.27 cm rainfall event from a 16 ha agricultural field. Water samples (1 L) were collected hourly within the first 24 h and again on days 2, 5, 7, 15, 21, 28, and 56 post-injection at both ends of the wetland for pesticide analysis. Peak pesticide concentrations were observed upstream 1 h after injection. Rapid pesticide removal from upstream water occurred with 63%, 51%, and 61% decrease in concentrations of atrazine, metolachlor and fipronil, respectively, by 24 h, and by day seven, 79%, 80%, and 87% decrease from peak concentrations occurred. After day 28, all pesticide concentrations were <0.300 micro g/L, and after day 56, no target pesticides were detected. Downstream, atrazine occurred in trace amounts (<0.4 micro g/L) within 24 h and after day 28 was not detectable. Metolachlor occurred once downstream on day 21 (0.249 micro g/L), and fipronil was detected on days 15-56 in trace amounts (<0.05 micro g/L). Results indicate that modified backwater wetlands can efficiently trap pesticides in runoff from agricultural fields during small to moderate rainfall events, mitigating impacts to receiving waters in the main river channel.