Long-Term Oxbow Lake Trophic State under Agricultural Best Management Practices

A key principle of agricultural best management practices (BMPs) is to improve water quality by reducing agricultural-sourced nutrients and associated eutrophication. Long-term (1998–2016) lake summer trophic state index (TSI) trends an watershed with were assessed. Structural BMPs included vegetative buffers, conservation tillage, reserve, a constructed wetland, sediment retention pond. TSI Secchi visibility (SD), chlorophyll (Chl), total phosphorus (TP), nitrogen (TN). Summer 1977 was >80 in 1998–1999 (hypertrophic) decreased over the first 10 years ≈ 75 (eutrophic). decrease changing deviations coincided reserve. The TSI(SD) (>90 <70) buffers TSI(TP) <75) primarily tillage TSI(Chl) increase (<60 >70) buffer. Results indicate watershed-wide can modestly through increased transparency TP, but these changes are off-set increases reach new stable within decade. Future research should assess algal nutrient thresholds, internal loading, climate change effects.