Date of Award

2007

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Aria Amirbahman

Second Committee Member

Ivan J. Fernandez

Third Committee Member

Stephen A. Norton

Abstract

Dissolved inorganic carbon (DIC) causes increased mobilization of dissolved, organically bound and particulate aluminum (Al), calcium (Ca), iron (Fe), and phosphorus (P) from the soils. Our objective was to examine whether increased metal solubility is attributed to increased DIC concentration in solution. Intact soil cores of 16.35 - 24.10 cm were taken from the O and B horizons from the East and West Bear Brook Watershed in Maine (BBWM) to conduct seven soil column transport experiments. DIC concentrations ranging from approximately 20 to 600 ppm with a background electrolyte solution of 0.1 M NaCl were introduced into the soil columns. To one column, a solution containing 2.5 ppm of dissolved organic carbon (DOC) extracted from the East Bear O horizon was added. DIC was introduced in two pulses of varying concentrations. Samples were continuously taken at the end of the column, and when stead-state condition with respect to DIC concentration was achieved, samples were taken along the depth of the columns. Columns were characterized with a conservative tracer that showed an average porosity of 0.61 ± 0.12 and a dispersion coefficient of 0.88 ± 1.12 m s". DIC was subject to reversible sorption and its movement was retarded by a factor of 1.2 to 2.1 compared to the conservative tracer corresponding to a log KD = -0.82 to -0.07. DIC significantly enhanced the mobilization of all metals and P. Colloidal Al and Fe were mobilized as a response to changes in the solution chemistry and flow regime. Ca and P were primarily in dissolved form. Mechanisms such as ion exchange (Al, Fe, Ca), ligand- and proton-promoted dissolution (Al and Fe) and ligand exchange (P) may explain mobilization of the species studied here. One column was packed with dried and sieved B-horizon material. The effluent from this column showed DOC, Al and Fe concentrations considerably higher than the intact columns, suggesting that these species were mobilized from the soil's microporous structure that is otherwise not exposed to the advective flow. Ca and P concentrations, however, were similar to the intact columns, suggesting that these species are associated primarily with the soil's external surface.

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