|Shields Jr, Fletcher|
Submitted to: Society of Environmental Toxicology and Chemistry Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2010
Publication Date: 5/20/2010
Citation: Lizotte Jr, R.E., Shields Jr, F.D., Murdock, J.N., Robert, K., Knight, S.S. 2010. Trapping Efficiency of Agricultural Runoff in a Modified Riverine Backwater Wetland. Abstract Book Mid South Chapter of the Society of Environmental Toxicology and Chemistry 2010, p. 25. Interpretive Summary: Abstract Only - Interpretative Summary not required.
Technical Abstract: Riverine backwater wetlands within river floodplains have important economic and ecological functions such as acting as filters for suspended sediment, nutrients and pesticides entering from adjacent agricultural fields. These wetlands hydrology can be modified to increase the efficiency of their natural filtering capabilities. We examined the trapping efficiency of a modified riverine backwater wetland amended with a mixture of suspended sediment, two nutrients (nitrogen and phosphorus), and three pesticides (atrazine, metolachlor, and permethrin) during a simulated agricultural runoff event. Modification of the 500 m-long, 25 m-wide riverine backwater wetland was done by adding weirs at both ends for hydrologic control. The mixture was amended to 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 every 30 min within the first 4 h, then every 4 h until 48 h, and again on days 5, 7, 14, 21, and 28 post-amendment at distances of 10 m, 40 m, 300 m and 500 m from the injection point within the wetland for suspended solids, nutrient, and pesticide analyses. Peak sediment, nutrient, and pesticide concentrations occurred within 3 h of amendment at 10 m, 40 m, and 300 m downstream and showed rapid removal of amendments from the water column with 91-98%, 42-81%, and 84-98% decrease in concentrations of sediments, nutrients, and pesticides, respectively, within 48 h. After day 28, all amendments were near or below pre-amendment concentrations. Water samples at 500 m showed no changes in sediments or nutrients; pesticides peaked within 48 h but at <15% of upstream peak concentrations and had dissipated by day 28. Modified riverine backwater wetlands can efficiently trap agricultural runoff during moderate rainfall events, mitigating impacts to receiving rivers.