Recreational impacts on ecosystem processes: Potential effects of recreational boat traffic on metabolism in the Little Susitna River, Alaska

Boats may alter lotic ecosystem function through several pathways including bank erosion and resuspension of bed deposits from propeller wash and boat-generated waves, which may increase turbidity and decrease primary productivity.  We quantified the potential effects of fishing-boat traffic on community metabolism in the Little Susitna River, south-central Alaska.  Dissolved oxygen and turbidity were continuously monitored from late May to early September (2008) at "reference" and "impacted" sites.  Gross primary production and net daily metabolism (mean ± S.E.) were higher at reference vs. impacted sites (0.36 (± 0.02) vs. 0.16 (± 0.03) and -0.02 (± 0.04) vs. -0.22 (± 0.03), respectively)(g O₂ m^-2 day^-1; single station, open system).  No detectable difference in community respiration was observed across study sites.  Turbidity values were higher at impacted sites on days when boats were present surpassing background levels by as much as 17 NTU.  Elevated turbidity levels at impacted sites could account for the observed reduction in GPP, although initial analyses suggest at most an indirect correlation.  Decreased primary productivity may negatively affect the local macroinvertebrate and fish community ultimately leading to a decline in salmon bioproductivity and recruitment.