Spatial and Temporal Dynamics of Biogeochemical Processes in the Fraser River, Canada: A Coupled Organic-Inorganic Perspective

Britta Voss, Ph.D., 2014
Bernhard Peucker-Ehrenbrink, Co-advisor
Timothy Eglinton, Co-advisor

The great geologic and climatic diversity of the Fraser River basin in southwestern Canada render it an excellent location for understanding biogeochemical cycling of sediments and terrigenous organic carbon. This study documents spatial and temporal variations in chemical weathering and mobilization, export, and biogeochemical transformation of organic carbon. Based on radiogenic strontium isotopes, the influence of sediments derived from the headwaters is detectable at the river mouth; however, more downstream sediment sources predominate, particularly during high discharge conditions. Bulk radiocarbon analyses are used to quantify terrestrial storage timescales of organic carbon and distinguish between petrogenic and biospheric organic carbon. The estimated terrestrial residence time of biospheric organic carbon in the Fraser basin is 650 years, which is relatively short compared to other larger rivers. A large portion of the dissolved inorganic carbon load of the Fraser River (>80%) is estimated to derive from remineralization of dissolved organic carbon, particularly during the annual spring freshet when organic carbon concentrations increase rapidly. This thesis establishes a baseline for carbon cycling in a largely unperturbed modern mid-latitude river system and establishes a framework for future process studies on the mechanisms of organic carbon turnover and organic matter-mineral associations in river systems.