UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Ten-year assessment of agricultural management and land-use practices on pesticide loads and risk to aquatic biota of an oxbow lake in the Mississippi Delta, USA
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: March 14, 2011
Publication Date: August 6, 2012
Citation: Lizotte Jr, R.E., Knight, S.S., Locke, M.A., Steinriede Jr, R.W. 2011. Ten-year assessment of agricultural management and land-use practices on pesticide loads and risk to aquatic biota of an oxbow lake in the Mississippi Delta, USA, 349-371. In: B. Hendriks (ed.) Agricultural Research Updates. New York, NY: Nova Publishers, Vol. 2. 478 pp.
Interpretive Summary: We examined pesticide contamination in lake surface water and their potential risk to aquatic animals and algae in relation to conservation and cropping practices within the watershed of an oxbow lake in the Mississippi Delta from 2000 to 2009. We looked for thirteen pesticides in lake surface water. During the ten-year study period, crops changed from mostly cotton in 2000-2001 to mostly soybean in 2002-2004, 2006, 2008, and 2009 with mostly milo and corn in 2007. Conservation practices such as reduced tillage began in 2001 and Conservation Reserve Program enrollment began in 2003 with planting of cottonwood trees. Over the ten-year study period, risk to lake aquatic animals and algae was greatest in 2000-2002, lowest in 2005-2006, and low in 2007-2009. Overall, lake water pesticide contamination decreased annually until 2005-2006 and increased again in 2007-2009 due, in part, to changes in crops from reduced tillage soybeans to conventional-till milo and corn in 2007. These results are of interest to regulatory and other agencies and the pesticide industry by providing additional information to improve and sustain lake and flood plain water quality and overall environmental quality using conservation practices.
The current chapter examined the combined influence of changing row crop production, implementation of agricultural Best Management Practices (BMPs), and enrollment of 112 ha into Conservation Reserve Program (CRP) on pesticide contamination and potential risk to lake aquatic biota in a 914-ha Beasley Lake watershed from 2000-2009. A suite of six current-use herbicides, five current-use insecticides, and two legacy insecticides were measured in lake surface water sampled approximately monthly from 2000-2009. Relative risk of these pesticides to lake aquatic biota was assessed using individual toxicity quotients (TQs), mixture pesticide toxicity index (PTI) scores based upon acute (48-96h) LC/EC50 values, and acute restricted-use pesticide levels of concern (LOCs) (LC/EC50 x 1, 0.5, and 0.1) for freshwater crustaceans (Daphnia sp.), insects (Culex sp.), fish (Lepomis sp.), and algae (Psuedokirchneriella sp.). During the ten-year study period, row-crop production shifted from primarily cotton in 2000-2001 to predominantly soybean in 2002-2004, 2006, 2008, and 2009 with milo and corn dominant in 2007. Reduced tillage BMPs were implemented in 2001 and CRP enrollment began in 2003. From 2000-2009, most individual pesticide concentrations were frequently <0.1 µg/L, with the exception of atrazine. Greatest herbicide concentrations occurred for triazine herbicides atrazine and cyanazine. Greatest insecticide concentrations occurred for methyl parathion and bifenthrin. Greatest legacy compound concentrations occurred for the organochlorine insecticide, p,p’-DDT. Temporally, peak lake water concentrations of current-use herbicides, current-use insecticides, and legacy compounds occurred during 2000, 2002, and 2002, respectively. Lowest lake water concentrations of current-use herbicides, current-use insecticides, and legacy compounds occurred during 2005. Results of the pesticide risk assessment showed greatest risk would be to crustaceans, primarily from the pyrethroid bifenthrin, during 2000-2002, with decreasing risk to fish and aquatic insects and minimal risk to algae. Although most individual pesticides were below LOCs, PTIs indicated increased risk from pesticide mixtures to aquatic fauna. Temporally, relative risk to lake aquatic biota decreased from greatest potential risk in 2000-2002 to minimal risk in 2005-2006 with infrequent risk to aquatic fauna in 2007-2009. Overall, lake water pesticide contamination decreased annually until 2005-2006 and increased again in 2007-2009 due, in part, to a shift in row crop from reduced tillage soybeans to conventional-till milo and corn in 2007. Concomitantly, changes in land-use with implementation of BMPs, CRP and crop type reduced the frequency and duration of risk of pesticides to lake aquatic biota.