Land use change and erosional history in a lake catchment system on the Canadian prairies

The introduction of agriculture in the late 1800s and early 1900s brought about many changes in the natural prairie landscape of western Canada. The objective of this research project is to evaluate landscape response to land use change by relating observed changes in the sedimentary record of a lake drainage basin to documented land use change that has occurred since the onset of settlement. A 52 cm lake sediment core was sectioned into 1 cm layers. The sediment was separated into allogenic and authigenic fractions using a wet chemical extraction technique. Close interval 210Pb dating enabled the calculation of sediment and elemental influx rates. Prior to European settlement, erosion rates were low (< 0.1 Mg ha− 1 year− 1). In the 1910s, when the first settlers arrived in the area, erosion rates increased, and in the 1920s and 1930s, when the area of improved land rapidly increased and conditions were dry, erosion rates reached peaks of 1.5 and 2.2 Mg ha− 1 year− 1. Erosion rates in the latter part of the 20th Century range from 0.6 to 0.7 Mg ha− 1 year− 1. The composition of the allogenic fraction in the most recent, black sediment at the top of the core shows high concentrations of Ti and Zr, indicating a large contribution of topsoil to the allogenic fraction. In addition, elevated concentrations of Zn, Ni, Mo and U are likely explained by the application of phosphate fertilizers. Because of sediment deposition within the basin, e.g., on concave footslopes and on the valley floor, the erosion rates derived from the Thunstrom Lake core should be interpreted as net rates that likely mask values that are much higher locally within the basin. As a result, this study provides information on the erosional response of the prairie landscape to recent changes in land use at the scale of the Thunstrom Lake basin, but not necessarily on the sustainability of the soil as a resource, which would require information at the much smaller scale of the individual field.