MS Thesis Defense
The research consisting of two parts was conducted to understand the reasons for continued increasing nitrate loads in the Gulf of Mexico and if an anion resin technology can be used to remediate tile water of excess nitrate ions. The first objective was accomplished through regression analysis of annual and monthly streamflow, baseflow, N-concentrations and N-load data for the Raccoon River, Des Moines River and Iowa River in Iowa. The results showed that annual streamflow, baseflow, and N-loads were primarily controlled by the current year and the previous year precipitation in the watershed and the effect of land use change, in terms of increased soybean area, was minimal. Monthly analysis showed precipitation in a given month and in prior months, and in some cases previous year, were significant in explaining monthly streamflow, baseflow, and N-loads. Presence of previous years’ and previous months’ precipitation in the regression indicated some interaction of previously stored soil water and N with the current year and current month’s precipitation.
The second objective was accomplished through field testing of an industrial anion-exchange resin with tile water from corn and soybean fields fertilized with inorganic N-fertilizer or hog manure. Results showed that the resin adsorption of nitrate was instantaneous and that resin efficiency to retain nitrate varied from 7-46%. Recharging of anion resin with potash solution resulted in KNO3 in wastewater that can be recycled back to land as fertilizer. However, the presence of sediment, sulfate, carbonates and organic carbon in tile water presented some challenges in achieving higher efficiency of the resin in agricultural landscapes.