Seasonal variability of river geochemistry in the Fraser River, British Columbia

River systems play a dynamic role in the cycling of carbon between terrestrial and marine reservoirs. The response of these systems to global warming and human activities is uncertain, but likely to involve complex interactions between hydrologic and biogeochemical changes from the basin-scale (e.g. shifts in distribution, volume, and type of precipitation; ecosystem adjustments to land use changes) to particle-scale (e.g. changes in organic matter composition due to altered terrestrial vegetation, changes in sediment characteristics due to damming on individual watersheds). To address these processes in a manner relevant to their global scope, a campaign (funded by the National Science Foundation’s Emerging Topics in Biogeochemical Cycling initiative) is underway to study basin-wide geochemical characteristics of the dissolved, suspended, and bed loads of several major rivers. The Fraser River is of particular interest due to its diversity of geological terrain, seasonality of discharge, and limited damming. Field campaigns in summer 2009 and fall 2010 offer a detailed characterization of the stable and radiogenic isotope signatures of particulate and sedimentary organic carbon; dissolved nutrients, organic and inorganic carbon, and trace metal concentrations; and dissolved 87Sr/86Sr at multiple points along the Fraser main stem and many tributaries. The critical next step is to extrapolate this information across seasonal cycles throughout the year. To that end, a time series sampling program has been established near the Fraser River mouth. Since late 2009, samples for dissolved nutrients, major ions, and 87Sr/86Sr have been collected by colleagues and undergraduate students at the University of the Fraser Valley in Abbotsford, B.C. With a full year of monthly or more frequent samples, we can assess how river geochemistry changes in response to seasonal cycles of temperature and discharge in such a heterogeneous system. This aspect of the world river project will support estimates of annual fluxes and predictions of how river geochemistry may change under different climatic circumstances.