Effects of a Simulated Agricultural Runoff Event on Sediment Toxicity in a Managed Backwater Wetland Richard E. Lizotte Jr. & F. Douglas Shields Jr. & Sam Testa III Received: 2 February 2012 / Accepted: 25 July 2012 / Published online: 12 August 2012 11.4 g), on 10-day sediment toxicity to Hyalella azteca in a managed natural backwater wetland after a simulat- ed agricultural runoff event. Sediment samples were collected at 10, 40, 100, 300, and 500 m from inflow 13 days prior to amendment and 1, 5, 12, 22, and 36 days post-amendment. Background pesticide concentrations ranged from <1 to 977, <1 to 119, and <1 to 2 μg kg -1 , for atrazine, S-metolachlor, and permethrin, respective- ly. Average post-amendment atrazine and S-metolachlor were 2,915–3,927 and 3–20 μg kg -1 , respectively at 10– 40 m and 538–872 and <1 μg kg -1 , respectively at 300– 500 m. Average post-amendment permethrin was 65– 200 μg kg -1 at 10–40 m and 1–10 μg kg -1 at 300– 500 m. H. azteca 10-day survival varied spatially and temporally up to 100 m from inflow. Animal growth, independent of survival, was reduced 40 and 100 m from inflow on day 36, showing continued sediment toxicity of up to 100 m from inflow more than 1 month tions and H. azteca responses indicated that observed sediment toxicity was primarily from permethrin with potential additional synergistic toxicity from atrazine and methyl parathion. Study results indicate that natural backwater wetlands can be managed to ameliorate pes- ticide mixture 10-day sediment toxicity to H. azteca within 300 m of inflow and smaller wetlands (≤100 m) may require several months of effluent retention to mitigate effects. Keywords Atrazine . S-metolachlor . Permethrin . Pesticides . Riverine wetland . Hyalella azteca 1 Introduction Importance of agriculture in providing proper nutrition and fiber for the world’ s growing human population continues to increase (Swinton et al. 2007). As modern agriculture increasingly relies upon new technologies such as chemical fertilizers and pesticides to improve productivity and efficiency in order to meet this grow- ing need (Cooper and Dobson 2007), there can be ecological trade-offs. One such ecological trade-off is degradation of water quality and aquatic habitat in rivers, lakes, and streams resulting from agricultural nonpoint source pollution (Knight and Welch 2004; Vondracek et al. 2005). Currently, several strategies Water Air Soil Pollut (2012) 223:5375–5389 DOI 10.1007/s11270-012-1287-1 R. E. Lizotte Jr. (*) : F. D. Shields Jr. : S. Testa III USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655, USA e-mail: Richard.lizotte@ars.usda.gov F. D. Shields Jr. e-mail: Doug.shields@ars.usda.gov S. Testa III e-mail: Sam.testa@ars.usda.gov # Springer Science+Business Media B.V. (outside the USA) 2012 Abstract We examined the effects of an amended mix- ture of three pesticides, atrazine (72.7 g), S-metolachlor (54.5 g), and permethrin (both cis and trans isomers; after amendment. Animal survival and growth were unaffected at 300 and 500 m from inflow throughout the study period. Correlations of pesticide concentra-