Sediment and Salmon Interactions: Implications for nutrient storage and downstream lake productivity

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Sediment moving through river channels acts as a vector, moving nutrients and contaminants along the same route to downstream lakes. Some soluble chemicals are loosely adsorbed to the sediment while other material is physically attached to the fine sediment. Fine inorganic sediment, defined as being smaller than 63 microns, readily combines with organic particles in the water column to form aggregated or flocculated particles which are larger and have different settling properties than their constituent materials. This results in variable, and therefore poorly predicted, transport and settling rates for both the sediment and the attached organic matter. Using salmon decay products as a contemporary example, this study investigates the interaction of sediment and salmon in altering the delivery of salmon-derived nutrients (SDN) from the spawning grounds to the downstream nursery lakes. In the interior of BC, salmonid nursery lakes require levels of primary production that can maintain the food web to support salmon fry. It is uncertain to what degree the decay products of returning spawners contribute to primary production in downstream nursery lakes. The fate of salmon decay nutrients has implications in the management of the spawning grounds and potentially for the success of future stocks. Over a 5-year period, which captures high- and low-density spawner returns, I propose to i) estimate the amount and timing of channel-stored SDN transferred in river discharge between the spawning grounds and nursery lake, ii) quantify the upstream river channel and floodplain storage of SDN, and iii) measure and model the physical mixing processes associated with a spawning stream emptying into a nursery lake in order to determine the effects of SDN loads on nursery lake primary productivity.