Anna Makowski
An Evaluation of Nitrate Transport in Sandy Soils at a Confined Feeding Operation
BSES Senior Research 2004

Several Confined Feeding Operations (CFOs) are operating in southwestern Indiana where ground water may be very sensitive to contamination because of highly permeable soils and a shallow water table. The potential sensitivity of this hydrogeologic setting to ground-water contamination warrants a thorough investigation of the effective limits of current management practices. It is our hypothesis that nitrate migration through the unsaturated zone is a result of gravity drainage, induced by rainfall, infiltration, and snowmelt. Such events typically occur early and late in the growing season when nutrients cannot be utilized to promote plant growth. The current project, which is supported by the U.S Environmental Protection Agency’s Clean Water Act Section 104(b)(3) program, is aimed at empirically evaluating this hypothesis. Our approach involves continuously monitoring hydrologic conditions and frequent water sampling that will allow development of a detailed hydrochemical budget for the waste-application fields in the area of concern.

This study is being conducted near Washington, Daviess County, Indiana. Three representative sites are simultaneously monitored: two on agricultural fields that receive animal-waste (in this case, turkey manure) applications (sites DW, DH) and the other on a field that receives commercial fertilizers (site DL, a control site). The field instrumentation was installed in late July 2003, and hydrologic and micrometeorological monitoring has been continuous since then. Biweekly visits to each of the three sites provide an opportunity to take additional measurements such as soil-moisture profiles and field chemistry, collect water samples from the soil column and water table, and calibrate the monitoring equipment. The water samples are analyzed in the field for specific conductivity, dissolved oxygen, pH, and oxidation-reduction potential (Eh). The samples are then returned to the lab, where they are analyzed for nitrate as nitrogen, nitrite as nitrogen, ammonia as nitrogen, chlorine, phosphate, and potassium. The results presented here involve only nitrate as nitrogen (NO3–N).

Nitrate levels at DL are significantly lower than those at DW and DH. Preliminary results show a correlation between recharge events and nitrate levels in the vadose zone and groundwater. Overall, nitrate levels in the saturated zone are lower in the summer, and higher in the late fall and early winter. This trend is probably linked to the increase in recharge associated with the annual hydrologic cycle. Nitrate concentrations in the vadose zone also reflect gravity drainage. Nitrate levels peak in the shallow vadose zone first. The middle and deep lysimeters respond sequentially in response to the downward migration of the wetting front.