Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 30, 2001
Publication Date: N/A
Technical Abstract: A regional watershed-based project (Mississippi Delta Management Systems Evaluation Area, MSEA) was established to assess effects of agricultural production practices on lake water quality. The focus was on three watersheds that drain into oxbow lakes (Thighman, Beasley, and Deep Hollow). Herbicide concentrations in lakes were monitored from 1996 to 1998. Water samples were analyzed by HPLC (fluometuron, 1996-1998) and GC-MS detection (atrazine, cyanazine, and metolachlor, 1998 only). All watersheds were primarily planted to cotton in 1996 and 1997, and fluometuron was the major herbicide used. Maximum fluometuron concentrations ranged from 5.4 to 12.7 ug L**-1, with highest fluometuron concentrations observed in Thighman Lake. Desmethyl fluometuron was the only fluometuron metabolite observed in lakes. Deep Hollow had a conservation management system, and reductions in fluometuron concentrations in 1998 were attributed to lower sediment runoff. In 1998, 50 and 70% of Beasley and Thighman watersheds, respectively, were planted in corn, and atrazine and metolachlor were used as herbicides. Cyanazine was usually applied to cotton during the middle of the season, and higher detections in lake samples usually appeared in late season. Beasley had the highest cyanazine concentrations (3 to 5 ug L**-1). Low atrazine concentrations were detected in Thighman Lake (0.1 to 0.6 ug L**-1) and Deep Hollow Lake (0.4 to 0.8 ug L**-1). Maximum atrazine concentrations in lake water were 2.5 and 15.0 ug L**-1, for Beasley and Thighman, respectively, while maximum metolachlor concentrations were 1.8 and 7.2 ug L**-1. Peak concentrations for atrazine and metolachlor appeared in May at Thighman Lake and late summer in Beasley Lake.