Effect of soil and absence/presence of an abandoned feedlot on determining the area sourcing nitrate to a contaminated domestic well

Abandoned feedlots have been found to enhance nitrate (NO3) production and subsequent contamination of nearby groundwater. Site remediation depends on a thorough understanding of existing manure deposits, knowledge often lacking when dealing with abandoned feedlots. The main objective of this work was to describe the variability in soil NO3 and organic matter concentrations with depth in an abandoned feedlot, to guide future remediation. The feedlot area was believed to be the source of NO3 contaminating a nearby domestic well. Organic matter and bioavailable Ca, Mg, K, and Zn were statistically higher in the surface 0 to 0.3 m of farmstead soils, as compared with surrounding farm field soils. The area around an old silo that was high in soil organic matter was not always well related to soil NO3 concentrations. Although greater organic matter between 0 and 0.3 m was generally associated with greater NO3 at deeper depths, it seemed that NO3 was being attenuated by landscape-induced denitrification in some areas of the farmstead. There were significantly lower NO3 concentrations with greater depth (0.3-1.2 m) in Loring (Oxyaquic Fragiudalf), as opposed to Memphis (Typic Hapludalf), farmstead profiles. This suggested that denitrification, due to perched water above the fragipan, was occurring in those parts of the farmstead landscape dominated by Loring soil. A detailed characterization of the site would be necessary to guide expensive remediation work because not all the area affected by the presence of an abandoned feedlot possesses high subsurface NO3 concentrations.