Date of Award

5-2013

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental and Soil Sciences

Major Professor

Michael E. Essington

Committee Members

Jaehoon Lee, Donald D. Tyler

Abstract

Loess soils of west Tennessee may potentially contain large amounts of subsoil metal oxides (Fe, Al, and Mn) which may retain and restrict the movement of conservative anions, such as nitrate (NO3). The potential utilization of large quantities of flue gas desulfurization (FGD) gypsum on these soils may displace subsoil NO3, releasing it to adversely impact sensitive aquatic environments. This research examines the depth distribution of Fe-, Al, and Mn-oxyhydroxides, pH, particle size distribution, and of the cation and anion exchange capacity and exchange phase composition to identify depths that have the greatest potential for anion exchange. The metal oxide content of depth incremented soil samples was determined using the citrate- bicarbonate-dithionite (CBD) and ammonium oxalate (AAO) extraction methods. The effective anion exchange capacity (EAEC), effective cation exchange capacity (ECEC), and anion and cation exchange phase compositions were determined using modified standard extraction methods. Both CBD and AAO extractable Fe, Al, and Mn were found to peak at two different depths within the soil profiles: in the Bt horizons (30 to 46 cm), and in the C horizon that underlie the loess deposits (244 to 259 cm). The depth- distribution of ECEC and EAEC follow the same trend as the extractable metal oxides. Based on these characterization data, the 30 to 46 cm and 245 to 261 cm depth increments are expected to be reactive to anions. This study also examined the anion exchange characteristics of binary and ternary nitrate, sulfate, and chloride systems in these high Fe-oxide horizons in the loess soils. Exchange isotherms were constructed by adding varying ratios of two (binary) or three (ternary) ions to soil samples, allowing them to equilibrate, and displacing exchanged anions on the exchange phase. Exchange isotherms indicate that chloride and nitrate are preferred relative to sulfate, and that chloride is preferred relative to nitrate where preference is established by the Vanselow selectivity coefficients. Although not preferred, sulfate predominates on the anion exchange phase due to its divalent charge. These findings will enhance our knowledge of how the addition of sulfate to soil will impact conservative anion behavior in loess soils.

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Soil Science Commons

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