Cation exchange due to the diffusion of ammonium from livestock effluent through glacial clay soils

The objective of this study was to experimentally simulate interactions between liquid manure and soil in diffusion-dominant areas beneath earthen manure storage (EMS). A previous radial diffusion cell method was modified to include an anaerobic chamber that employed a plastic glove bag supplied with inert Ar gas. Anaerobic conditions were maintained during the entire run time of the experiment. Little oxidation of NH4+ occurred; consequently, NO3- and NO2- concentrations were lower than the detection limit. Chloride played a key role in redistribution of major cations and anions resulting from the NH4+ diffusion. Linear NH4+ and K+ adsorption isotherms were obtained. The resulting distribution coefficients, Kd, for NH4+ ranged from 0.3 to 0.4 L/kg. Significant NH4+ exchange reactions led to an average increase in hardness of 137% in the reservoirs, due to extraction of exchangeable Ca and Mg. Geochemical mixing modeling using PHREEQC adequately simulated the linear NH4+ adsorption at low dissolved NH4+ concentrations (<30 mM). The predicted manure volumes to cause NH4+ saturation were 1.0–1.4 mL/g for the glacial clay soil samples.