APPLICATION OF COMPOUND-SPECIFIC STABLE ISOTOPES (CSSIS) TO SOIL AND SEDIMENT TRACING: AN EXAMINATION OF THE HORSEFLY RIVER WATERSHED (HRW) AND THE SOUTH TOBACCO CREEK WATERSHED (STCW)

Current methods used in soil and sediment tracing include geochemical analyses and the use of fallout radio nuclides. A novel approach to tracing has recently appeared in the literature: the use of CSSIs, specifically fatty acids (FAs). Fatty acids of plant origin have been used with moderate success in determining the source of sediments based on land use and vegetation type in agricultural watersheds. The FAs are transferred from the plant—aerial and root portions—to the soil and, once the soil is mobilized, migrate to deposition zones. The isotopic carbon signatures (¹³C:¹²C) of the individual FAs, which are carefully selected, may be used in conjunction with modeling programs to unmix the FA signal of the deposition zone and apportion the soil into various potential sources. Due to the somewhat complex nature of the technique, understanding the variability and minimizing error will allow for a more robust data set. The CSSI method has the potential to provide very specific sources of erosion based on land use and will complement other tools that are currently being employed.

An extensive sampling regime was undertaken in the HRW in the central interior of British Columbia, and the South Tobacco Creek Watershed STCW, west of Winnipeg, Manitoba, which feeds into Lake Winnipeg. Sampling in the HRW was undertaken from August 2011 until August 2013 to represent various plant growth periods; in the STCW, sampling was performed on multiple occasions through the spring/summer/fall periods for 2012 and 2013. The purpose of the sampling was to explore the variability of the CSSI technique, and to have a better understanding of the temporal and spatial changes that occur in the CSSI signal in a predominantly natural watershed (HRW) and a heavily cropped agricultural watershed (STCW).