Tuesday, June 5, 2007
447

Influence of Forest Management on Salmon-Derived Nutrient Dynamics in Southeast Alaska Streams

Peter Levi, Jennifer L. Tank, Scott D. Tiegs, Dominic T. Chaloner, and Gary A. Lamberti. Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556

Southeast Alaska streams receive a nutrient pulse during annual salmon migrations, but forest management may alter the effects of salmon-derived nutrients. For example, streams draining harvested catchments have more open channels and less large woody debris, which may reduce in-stream carcass retention and increase primary production. We sampled 7 streams across a timber harvest gradient (6-85% watershed area harvested) for dissolved nutrients before, during, and after salmon runs on Prince of Wales Island, Alaska.  In both harvested (>30% harvested) and reference (<10%) streams, we found that dissolved nutrient concentrations (SRP, NH4+, NO3-) were highest during salmon runs, and concentrations returned to pre-salmon levels when only carcasses remained. For example, mean SRP concentrations increased 3-fold in the presence of salmon (2.5 to 8.1 µgP/L). Using stream discharge to estimate SRP flux, export was significantly higher (6.1 to 59.1 mgP/hr) during salmon runs in harvested streams; a pattern correlated with larger salmon runs. In contrast, salmon presence did not change nutrient flux in reference streams. We found that salmon runs have the potential to increase dissolved nutrient concentrations, but nutrient flux was influenced by both variation in stream discharge and salmon run size which may be influenced by forest management practices.

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