Wednesday, May 28, 2008 - 10:15 AM
388

Aquatic-terrestrial coupling in the flux, uptake, and effects of Pacific Salmon nutrients in Southeast Alaska watersheds

Gary A. Lamberti1, M. Eric Benbow2, Scott D. Bridgham3, Emily Y. Campbell2, Dominic T. Chaloner1, David V. D'Amore4, Richard T. Edwards4, John P. Hudson5, Peter S. Levi1, Richard W. Merritt2, Alexander J. Reisinger6, Janine Rüegg1, Jennifer L. Tank1, and Scott D. Tiegs1. (1) Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, (2) Department of Entomology, Michigan State University, East Lansing, MI 48824, (3) Department of Biology, University of Oregon, Eugene, OR 97403, (4) Pacific Northwest Research Station, USDA Forest Service, Juneau, AK 99801, (5) Aquatics Alaska, 16445 Point Lena Loop Road, Juneau, AK 99801, (6) Division of Biological Sciences, Kansas State University, Manhattan, KS 66506

Most previous studies of Pacific salmon (Oncorhynchus spp.) effects on their natal streams have been conducted in watersheds lacking a history of human disturbance.  Instead, we studied salmon in the context of watershed management by assessing how timber harvest influences stream-riparian linkages in salmon nutrient flux and uptake.  A strong gradient (5-68%) in watershed timber harvest on Prince of Wales Island, Alaska, revealed that watershed condition influenced carcass retention and stream-riparian uptake of salmon nutrients.  For example, the reduced sediment size found in heavily harvested watersheds transformed the dominant role of salmon from nutrient enrichment to physical disturbance.  Although salmon nutrients flow to riparian areas via carcass transport by floods and large carnivores, logging-related conversion of coniferous forests to monospecific stands of nitrogen-fixing alder may augment nitrogen budgets and thereby reduce the demand for such nutrients.  For example, streamwater nitrate concentrations in alder-dominated watersheds were ~2X those of conifer-dominated watersheds.  Stream metabolism was also higher in harvested watersheds and when salmon were present.  Collectively, our results suggest that timber harvest can alter the connectivity among marine, freshwater, and terrestrial ecosystems historically provided by migrations of Pacific salmon, emphasizing the importance of watershed restoration to repair these linkages.


Web Page: Pacific salmon, Alaska, nutrient cycling

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