Water quality monitoring of an agricultural watershed lake: the effectiveness of agricultural best management practices

摘要

Beasley Lake is an oxbow lake located in the Lower Mississippi Alluvial Plain (the Delta), a region of extensive agricultural activity. Due to intensive row-crop agricultural practices, the 915ha watershed was sediment impaired when monitoring began in 1995 and was a candidate to assess the effectiveness of watershed-wide agricultural Best Management Practices (BMPs) on lake Water Quality (WQ). BMPs within crop fields, at field edges throughout the watershed, and enrolment of 113ha into Conservation Reserve Program (CRP) were implemented from 1997-2003 targeting reductions in sediment runoff. Bi-weekly WQ data from 1996-2009 were analyzed. WQ parameters assessed include Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Filterable Orthophosphate (FOP), Total Orthophosphate (TOP), Total Nitrate Nitrogen (NO_3), Total Ammonia Nitrogen (NH_3), chlorophyll a, and water clarity (secchi visibility depth). Over the 14-year period, TSS, TOP, NO_3, and NH_3 decreased annually whereas chlorophyll a and water clarity increased in conjunction with implemented BMPs. FOP appeared unaffected throughout the monitoring period. While annual improvement in WQ occurred, distinct seasonal effects were noticeable. Changes in TSS, TOP, NO_3, NH_3, and water clarity were greatest ? during spring and negligible in winter. Changes in TDS were observed only during summer. Reductions in spring TSS directly reduced TOP, increased chlorophyll a and water clarity. Results of this study indicate clear improvement in Mississippi Delta lake WQ with watershed-wide implementation of agricultural BMPs and these improvements, manifested most strongly during spring, will promote a healthy, sustainable lake ecosystem.