| Abstract/Description or Keywords |
The study of sediment transport in riverine systems has historically focussed on the inorganic fluxes, although the suspended load is known to incorporate both inorganic and organic material. Research on freshwater flocculation indicates that sediment morphology and behaviour depend on both components, as biologic material can alter the hydrodynamic and charge properties of composite particles, which has implications for fine sediment transport and storage in stream systems. This study evaluates both the supply and the quality of the organic matter comprising the suspended sediment in a salmon-bearing stream in northern British Columbia, Canada. Seasonally changing hydrodynamic and biologic conditions are considered in the context of suspended sediment (seston) size. Seston samples were collected in an event-based design for analysis of organic matter sources, suspended particulate, inorganic and organic matter concentrations (SPM, SIM and SOM) and effective particle size distributions (EPSD). Organic matter sources were assessed using carbon : nitrogen (C :N) ratios and the associated stable isotopic signals. Samples and environmental measurements were taken during spring melt, pre-spawn low flows, active salmon spawning, post-spawn, and select rainstorms. SPM and SIM were elevated during active salmon spawning compared to that expected for the given hydrologic conditions. Seasonal patterns of C:N ratios and stable isotopes indicate that organic matter types can be differentiated in seston samples and these sources of organic material exhibit changing dominance in the seston over time. The isotopic signature of seston increases in salmon-derived nutrients when live and decaying salmon are present within the study stream. The largest suspended particles are observed during the period of active spawning when both live and rotting salmon modify instream conditions. This appears to be a function of the combined influence of high SIM, low shear stress, and low C:N ratios. The generation of increased floc, or seston size is of ecological importance in this stream and riverine systems elsewhere as it regulates the freshwater transfers of locally derived nutrients and sediments out of the fluvial system. Fine sediment; Organic matter; Source tracing; Stable isotopes; Seston; Flocculation |
