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Nicholas Ettema ACF Abstract FY10

Metabolism as an indicator of river ecosystem health: a case study on the Little Susitna River, Alaska

Conference Name: Midwest Fish and Wildlife Conference

When assessing river ecosystem health, many researchers note that structural metrics (physical and biotic characteristics) can misdiagnose river condition and the inclusion of functional metrics (energy flow and nutrient cycling) provide a more robust assessment. Ecosystem metabolism is often favored because it quantifies important functional attributes including autochthonous energy production and total energy consumption.  Ecosystem metabolism was used to monitor river health in the Little Susitna River, south-central Alaska, where a popular sport fishery leads to extensive boat and foot traffic during the summer salmon runs resulting in poor bank stability and elevated turbidity.  Ambient dissolved oxygen concentration was continuously monitored at upstream "reference" and downstream "impact" sites during the summer of 2008.  Gross primary productivity (mean) was higher at reference vs. impacted sites (0.43 vs. 0.19 g O2 m-2 day-1).  Ecosystem respiration was relatively constant across sites (0.33 g O2 m-2 day-1) and net ecosystem metabolism revealed autotrophic conditions (P:R, 1.42) upstream and heterotrophic conditions (P:R, 0.58) downstream.  Decreases in productivity at impact sites were best explained (R2, 0.53) by increases in turbidity suggesting recreational activity is altering natural metabolic processes of the system.  Less autotrophic energy production may trigger a trophic cascade leading to decreased salmon production in the lower reaches of the Little Susitna.  Utilizing a functional approach to assess river health was successful and further exploration of these metrics would improve our understanding of ecosystem processes.

Nicholas R. Ettema1, Jeffrey C. Davis2, Gay A. Davis2 and Eric B. Snyder1

(1)Biology, Grand Valley State University, 207 Henry Hall, 1 Campus Dr., Allendale, MI 49401

(2)Aquatic Restoration and Research Institute, P.O. Box 923, Talkeetna, AK 99676