Effects of Agricultural and Conservation Practices on Nutrients Losses from the St. Joseph River Watershed, Northeast Indiana.

Agriculture has been identified as a primary contributor to nutrients that cause algal blooms in the Gulf of Mexico and Lake Erie. Since 2002, we have been monitoring water quality from agricultural drainage ditches in the St. Joseph River watershed to assess the impacts of agricultural and conservation practices on water quality.  We have monitored 7 sites along 3 agricultural drainage ditches, and one site on Cedar Creek, the largest tributary to the St. Joseph River. We used three data sources to assess the impacts of agricultural and conservation practices on nutrients in these surface waters.  The data sources were: (1) data provided by NRCS giving the location of conservation practices implemented in the monitored watershed area, including conservation tillage, residue management, and placement of buffer strips; (2) windshield surveys of the watershed identifying crop, tillage and residue cover by field; and (3) surveys of agricultural producers in the watershed to determine dates and locations of agricultural practices, and the types and rates of fertilizers applied in the watershed.  We compared the results from these three data sources to flow-weighted mean nutrient concentrations and loads using multiple regression techniques.  The presence of ephemeral gullies in field, as reported from windshield surveys, were positively related to discharge, NO3-N concentration and load, NH4-N load, and TKN load. Residue cover was categorized into 5 categories (0, 0-15, 16-30, 31-50, 51-75 and 76-100%), which were generally inversely correlated with nutrient concentrations or loads. The level of conventional tillage was positively correlated with NH4-N loads, but negatively correlated with soluble P loads. Data from these analyses will be used to help identify critical areas for placement of conservation practices, as well as identify the practices that can be used to improve water quality.