Dissolved organic carbon in aquitard environments : properties, complexation, and transport
Clay-rich glacial till aquitards are widespread throughout the northern hemisphere. Due to their low hydraulic conductivity, these geologic units are commonly used to contain wastes. Dissolved Organic Carbon (DOC) in natural environments influences the speciation and mobility of contaminants, such as heavy metals and radionuclides, and is present in high concentrations in clay-rich tills (5 to 150 mg l-1). Detailed knowledge of the influence of DOC on the long-term stability, speciation, and mobility of elements is lacking. Studies in this thesis characterize the properties and function of DOC with respect to element speciation and transport at the King research site, an archetypal clay-till aquitard in Saskatchewan, Canada. Characterization of DOC using Asymmetrical Flow-Field Flow Fractionation (AsFlFFF) with on-line UV and DOC detection demonstrated the molecular weight (Mw) of DOC within the aquitard environment is low, ranging from 1160 to 1286 daltons (Da), and the relative amount of aromatic carbon in aquitard DOC is lower than in surface water DOC. These findings imply the complexation ability of DOC in aquitards is lower than surface water DOC. DOC aromaticity decreased with depth in the aquitard, while Mw remained constant. DOC Mw in other aquitards investigated was comparably low (1470-1630 Da). Coupling AsFlFFF with on-line ICP-MS analysis allowed the identification of Fe, U and Zn associated with the DOC, and demonstrated that 2 nm were prevented from movement in the till by sieving mechanisms, which suggests bacteria and viruses as well as larger colloids should not migrate through till aquitards. Due to preferential sieving of larger Mw DOC, DOC in aquitard environments is typified by a small diameter compared with surface water DOC, and a small range in hydrodynamic diameter and Mw.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorHendry, M. Jim
CommitteeRoss, Andrew R. S.; Pan, Yuanming; Merriam, James B.; Ansdell, Kevin M.; Wassenaar, Len
Copyright DateMay 2007