That's phat: The development and evaluation of compound-specific stable isotopes (CSSIs) of very long-chain fatty acids (VLCFAs) as a sediment tracing tool in a temperate climate

Rivers and lakes are subject to various forms of pollution from anthropogenic activity and natural sources. Many pollutants, such as those from agricultural runoff, are transported in rivers by binding to sediment. Sediment itself is a pollutant, and is often an indicator of terrestrial erosive processes. Common methods of establishing sediment provenance on a broad scale include the use of fallout radio nuclides and geochemistry. In 2008, Dr. Max Gibbs published a sediment tracing article on the use of compound-specific stable isotopes (CSSIs) of plant origin which identified sediment sources based on land use in sub-tropical New Zealand. The objective of the research undertaken here was to apply the CSSI concept to agricultural watersheds in a northern, temperate climate. Two watersheds were selected: the Horsefly River Watershed (HRW) near Horsefly, BC, Canada and the South Tobacco Creek Watershed (STCW), near Miami, Manitoba, Canada. The HRW represented a mostly pristine watershed. The STCW represented a heavily cropped agricultural watershed. The HRW samples were used to develop laboratory methodology, while the STCW samples were used to evaluate the CSSI technique using carbon stable isotopes. The dissertation addresses the following: (i) literature review of plant biomarkers and spatial/temporal variability of CSSIs due to biological, environmental and analytical factors; (ii) methodology, analysis and variability associated with bulk soil and sediment isotope determination; (iii) methodologies for processing soil and sediment from sampling to isotope analysis; and (iv) spatial and temporal variability of CSSI tracers. The CSSI tracers were evaluated to reveal spatial and temporal variability of VLCFA concentrations and isotope signatures at the point, transect and field scales. Weighted t-tests were used to differentiate sediment sources spatially and temporally. The use of bulk carbon as a proxy for VLCFA concentrations in source apportioning was also explored. The work presented here demonstrates the ability of CSSIs to differentiate sediment sources based on land use. The development of analytical methods and the resulting analysis of soil and sediment extracts have indicated that VLCFAs may be isolated and quantified to generate reliable isotope data. The methods will hopefully lead to the standardization of CSSIs protocols.