The Salmon Disturbance Regime: Effects on Biofilm, Sediment and Water.

Recent work in salmon spawning streams has shown that sediment resuspended during nest construction aggregates with salmon organic matter to form suspended particles called flocs. These nutrient-rich flocs interact with streambed biofilms suggesting a potential floc trapping mechanism that drives biofilm growth. Using the Horsefly spawning channel, the role of biofilms in trapping fine sediment was evaluated as a mechanism of salmon-derived nutrient processing. In the active spawn period, biofilm was reduced in abundance while the streambed sediment infiltration was at its highest level. During salmon die-off, downstream biofilm abundance recovered to pre-spawn values indicating a nutrient pulse over a small scale. With the re-established biofilm layer, sediment was increasingly trapped at the streambed surface by biofilms. This increase in biofilm abundance will likely influence the nutrient dynamics at all levels of the stream foodweb. Biofilms transfer increases in productivity to higher trophic levels. This transfer has a positive effect on the next generation of juvenile salmon growth and survivorship. --P.ii.