Fine sediment and organic matter interactions: bio-physical effects of aggregated sediments on streams

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Flocculated or aggregated soils and sediment are a known vector for nutrient and contaminant transfers to and within aquatic systems. Their behavior and residence time in aquatic systems is a regulating factor in the delivery and retention of materials in rivers, lakes and oceans. In northern BC the massive pine beetle epidemic has altered the hydrologic functioning of many watersheds. A suggestion to harvest these regions and change to an agricultural has been suggested by governments. This, in combination with predicted climate warming, implies an increase in field tillage and fertilization in many watersheds. The effect of these potential changes on terrestrial-aquatic connectivity, via soil erosion, suggests that streams will be receiving increased loads of sediment and organic matter. Some of this material will be delivered to the streams as soil aggregates but as well an instream process of flocculation will occur. These composite particles can be retained and decomposed in the gravel bed delivering nutrients to the hyporeic and overlying water. Recent work indicates that a sediment-fish biomass feedback loop helps regulate the nutrient status, and therefore ecological functioning of salmon spawning, gravel-bed rivers. I propose to investigate if this process operates in other stream systems, dominated by different types of organic matter (agricultural fertilizers, algal blooms, forest litter). I will quantify the generation, settling, storage, and hyporeic release products of aggregates in artificial streams (flumes). The magnitude and significance of the bio-physical processes for each of the organic source materials can be determined and then field work in natural rivers will allow a comparison of the flume simulated results. Basic research investigating riverine floc/aggregate generation, fate and effect will use sedimentological and microscopic techniques, while applied research into the development of a new sediment tracing method using microbial DNA as a hydro-geomorphic tracer will be tested. This project delivers to watershed management and aquatic habitat restoration concerns that require combined geomorphic knowledge of sediment transfers and ecological information regarding aquatic nutrient transfers.