Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2009
Publication Date: 5/8/2009
Citation: Lizotte Jr, R.E., Shields Jr, F.D., Knight, S.S., Bryant, C.T. 2009. Efficiency of a modified backwater wetland in trapping a pesticide mixture. Ecohydrology 2(3):287-293. DOI:10.1002/eco.52. Interpretive Summary: Natural wetlands occurring in a flood plain near rivers can be modified to be used as best management practices to improve and sustain river water quality. A study was done in a modified natural flood plain 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 flood plain 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: The pesticide trapping efficiency of a modified backwater wetland amended with a mixture of three pesticides, atrazine, S-metolachlor, and fipronil, using a simulated runoff event, was examined. The 700 m long, 25 m wide wetland, located along the Coldwater River in Tunica County, Mississippi, USA, was modified for hydrologic control via weirs at both ends. A pesticide mixture was amended 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 of atrazine, S-metolachlor and fipronil, respectively, by 24 h. By day seven, 79%, 80%, and 87% decreases from peak concentrations occurred. After day 28, all pesticide concentrations were <0.3 ug L-1, and after day 56, no target pesticides were detected. Downstream, atrazine occurred in trace amounts (<0.4 ug L-1) within 24 h and after day 28 was not detectable. S-Metolachlor occurred once downstream on day 21 (0.249 ug L-1), and fipronil was detected on days 15-56 in trace amounts (<0.05 ug L-1). 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.