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Ecosystem response to a salmon disturbance regime: Implications for downstream nutrient fluxes in aquatic systems

Summary: Ecosystem response to a salmon disturbance regime: Implications for downstream
nutrient fluxes in aquatic systems
Sam J. Albers* and Ellen L. Petticrew
Geography Program and Quesnel River Research Centre, University of Northern British Columbia, Prince George, British Columbia,
Recent work in salmon spawning streams has shown that sediment resuspended during nest construction
flocculates with salmon organic matter to form suspended composite particles characterized by increased size and
settling velocities. In a river system, these flocs have the potential to interact with benthic biofilms, suggesting a
mechanism for the incorporation of organic matter into aquatic food webs. Using the Horsefly River spawning
channel in central British Columbia, the spatial scale of biofilm floc trapping was evaluated for a salmon
disturbance regime, which consists of the active digging of redds, spawning, and carcass decay. We stocked two
sequential enclosures in the spawning channel with sockeye salmon (Oncorhynchus nerka) and established one
upstream control enclosure. Biofilms were sampled for chlorophyll a, trapped sediment, and marine isotope
tracers (d15N and d13C). In the active-spawn period, biofilm abundance was reduced due to spawning disturbance,
with isotope values indicating low utilization of marine-derived nutrients (MDNs). During the post-spawn period,
downstream biofilm abundance exceeded pre-spawn values, indicating a near-field nutrient pulse with isotope
values reflecting biofilm utilization of MDNs. At the same time, an increase in biofilm trapping efficiency
occurred in concert with a significant increase in the in situ particle size of suspended sediment, suggesting that
flocs were a temporary storage site of MDNs. The retention of MDNs over short spatial scales acts to retard the


Source: Aukema, Brian - ukema, Brian - Canadian Forest Service & Ecosystem Science and Management Program, University of Northern British Columbia


Collections: Environmental Sciences and Ecology