Submitted to: Journal of Environmental Science and Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2010
Publication Date: 3/30/2010
Citation: Knight, S.S., Lizotte Jr, R.E., Smith Jr, S., Bryant, C.T. 2010. Responses of Hyalella azteca to chronic exposure of Mississippi Delta sediments. Journal of Environmental Science and Engineering. 4(3):1-12 (Serial No. 28). Interpretive Summary: Oxbow lakes are distinctive natural features of the Mississippi River Alluvial Plain or Delta. Because of the extensive cultivation of crops, pesticides in agricultural runoff may accumulate in many of these lakes and potentially harm fish and wildlife. The preferred method to protect natural resources from pesticide damage is the use of Best Management Practices (BMPs) which either breaks the pesticide down into harmless compounds or traps the pesticide in the fields where they will do no harm. This study was designed to first evaluate the effectiveness of best management practices and second to test how dangerous or toxic the contaminated runoff might be. Bottom sediment from nine oxbow lakes was tested for toxicity and pesticide content. Three lakes were listed as impaired by the US Environmental Protection Agency, three were protected with BMPs and three were in a national wildlife refuge. While sediments from all nine lakes contained pesticides, sediment toxicity was greatest in lakes designated as impaired and less in BMP treated oxbows. No sediment toxicity was observed in the wildlife refuge lakes. Curiously, despite relatively high levels of pesticides in some samples, no toxicity was observed, which suggests that the pesticide may be bound to sediment and dead plant matter in the lake and unavailable to harm fish and wildlife.
Technical Abstract: Hyalella azteca was used to assess biological impairment in sediments from nine water bodies in the Mississippi alluvial plain. Water bodies were categorized according to land use and implementation of agricultural best management practices (BMPs). Three reference oxbow lakes were located in the White River National Wildlife Refuge (NWR), Arkansas; three Mississippi lakes were treated with varying BMPs to improve water quality/ecology; and two lakes and one bayou, also located in Mississippi, were listed as impaired according to USEPA section 303d Clean Water Act (303d). Sediment samples were collected at three sites within each water body from June to July 2004 and analyzed for 17 current and historic-use pesticides and metabolites. Twenty-eight day H. azteca survival and growth were measured to assess the degree of biological impairment. No significant (P > 0.05) mortality occurred in animals exposed to sediments. Significant growth impairment was observed in sediments from all three 303d listed water bodies and two of three BMP oxbow lakes. Associations of sediment pesticide contamination with observed H. azteca responses were limited. Historic-use pesticides and metabolites were implicated in two of five biologically impaired water bodies (303d listed bayou and BMP lake). In this study, even accounting for sediment characteristics such as sand-silt-clay fractions and organic carbon content did not further clarify sources of toxicity in some water bodies. Finally, results show that implementation of BMPs can mitigate biological impairment within lake sediments.