LAND-USE CONTROL ON TOTAL INORGANIC NITROGEN IN KARST AQUIFERS IN THE CUMBERLAND PLATEAU (SOUTHEASTERN KENTUCKY) IN THE UPPER OHIO RIVER BASIN

Agricultural non-point-source pollution from the upper areas of the Upper Mississippi, Missouri, and Ohio River Basins accounts for the majority of the excess nitrogen that leads to the Gulf of Mexico’s hypoxia zone. Mitigating long-term nutrient inputs at a large scale (Mississippi River Basin) requires understanding micro-scale changes at the small watershed level (less than 100 km²). To assess land-use control on nutrient fate and transport to groundwater, we analyzed and compared temporal patterns in nutrient concentrations from groundwater samples collected within two agricultural watersheds located in the Cumberland Plateau (Upper Ohio River Basin), a region mainly covered by mixed land-use (secondary-growth forests, agricultural cover, low density grazing and residential cover) and karstic landscapes. The uplands have experienced a rapid proliferation of concentrated-animal feeding operations (CAFOs) while the lowlands have remained relatively pristine with regards to CAFO development. On a regional scale, we are analyzing land-use changes control on Total Inorganic Nitrogen (TIN) loads between a CAFO-affected system (Grayson-Gunnar cave, GGC) and a predominantly agricultural non-CAFO system (Mill Springs, MS). Because the GGC basin can be further divided into two halves according to land-use (corn row-crops and CAFO in the North, and low grazing and residential in the South), we are also assessing the control of heterogeneous spatial distribution in land-use on TIN loads at a local scale. Based on 4-months of weekly sampling in the Cumberland uplands (GGC) and 8 years of quarterly data in the pristine lowlands (MS), there is no significant difference in TIN concentrations in groundwater between CAFO-influenced (GGC) and non-CAFO-affected (MS) systems. However, on a smaller watershed scale (GGC), point-source contamination from the CAFO exerts a higher control on TIN loads in groundwater when compared to non-point sources (fertilized croplands). Although the transition from open farming to CAFOs occurred within the last 10 years in the Cumberland Plateau, their impacts on nutrients at the small watershed scale can be observed. Emphasis on site-specific Nutrient Management Plans will be vital in reducing nutrients to the Gulf of Mexico.