Movement and aquifer contamination potential of atrazine and inorganic chemicals in central Kansas croplands

Abstract

We conducted flooding experiments at two sites with different soils to study the transport and fate of the commonly used herbicide atrazine and inorganic chemicals in the Great Bend Prairie croplands. To characterize in situ the hydraulic and chemical properties of the appropriately instrumented field sites, we used the instantaneous profile method supplemented by means of an organic (atrazine) and an inorganic (bromide) tracer chemical. Atrazine readily hydrolyzed into hydroxyatrazine and biodegraded to ethylatrazine and isopropylatrazine, thus explaining why atrazine was not detected deeper in the soil profile and in the underlying shallow aquifer. The classical processes of chemical movement based on equilibrium conditions and diffuse flow through porous media did not fit the data well at either site. Incompletely mixed slug flow predominates at one of the sites, and preferential flow predominates at the other. As a result of the observed slug movement, piston-type displacement of more saline solutions in the soil profile to the shallow water table occurred. Relatively high nitrate concentrations in both the vadose and the saturated zone were observed in one of the sites, which is characterized by sandy soil. The nitrate data indicate a close relationship between nitrogen fertilizer application, irrigation, and nitrate movement into the subsurface.