GLOBES Research Summary
Peter Levi
Email: plevi@nd.edu
Department: Biological Sciences
Advisor: Jennifer Tank
Salmon and watershed timber harvest influence stream dynamics in Southeast Alaska
The temperate rainforest along the Pacific coast of the United States and Canada is one of the most productive ecosystems on Earth. The terrestrial flora and fauna within this region grow to exceptional sizes (e.g., hemlock, spruce, and brown bears), however, streams within the rainforest have little production, characterized by low nutrient and chlorophyll-a concentrations. Pacific salmon (Oncorhynchus spp.) provide a large resource subsidy during their annual migrations, delivering nitrogen and phosphorus to the low production freshwaters. Through predation and flood events, salmon carcasses enter the riparian habitat, fueling terrestrial production, too. Recent research has debated whether salmon are sources or sinks of nutrients for their natal streams (Moore et al. 2007). While salmon deliver nutrients through excretion and carcass decomposition (Chaloner et al. 2004), nutrients are lost through benthic disturbance and juvenile salmon migrations to the ocean (Gende et al. 2002). Further, historical and current timber harvest practices have altered physical aspects of the stream (e.g., geomorphology and sediment size) (Tiegs et al. in press), potentially affecting the retention and availability of salmon-derived nutrients. Streams in heavily harvested watersheds are often broad and shallow with homogeneous sediments. In contrast, streams with little to no timber harvest in the surrounding watershed have complex, braided channels with more frequent pool-riffle sequences (Tiegs et al. in press). Our research sites on Prince of Wales Island, Alaska, provide the opportunity to study both effects in streams with annual salmon runs within watersheds that span a harvest gradient.
Our research seeks to understand the structure and function of these unique ecosystems. Through collaboration with Michigan State University and the Juneau Forest Sciences Laboratory, we are examining many metrics, including stream metabolism, nutrient transformations, in-stream food-web dynamics, soil nutrient dynamics, and salmon decomposition rates. The broad nature of this research will inform scientists and government agencies on implementation of sound forest management practices and stream restoration projects to ensure healthy salmon runs and productive forest growth.
My research interests and goals within the larger collaboration involve studying stream metabolism and nutrient transformations; processes that describe overall ecosystem function. Stream metabolism is a measure of the production and consumption of oxygen within the stream, which allows us to quantify gross primary production and community respiration. The current literature on salmon demonstrate their ecological impact on structural aspects of stream ecosystems, including elevated water nutrient concentrations and sediment export (Moore et al. 2007, Chaloner et al. 2004), but has only indirectly addressed the effect on ecosystem function. Our direct study of stream metabolism will allow us to determine if either salmon migrations or a timber harvest legacy have an impact on stream function or if these systems are resilient to natural and human disturbances.
Chaloner, D. T., G. A. Lamberti, R. W. Merritt, N. L. Mitchell, P. H. Ostrom, and M. S. Wipfli. 2004. Variation in responses to spawning Pacific salmon among three south-eastern Alaska streams. Freshwater Biology 49:587–599.
Gende, S. M., R. T. Edwards, M. F. Willson, and M. S. Wipfli. 2002. Pacific salmon in aquatic and terrestrial ecosystems. BioScience 52:917–928.
Moore, J. W., D. E. Schindler, J. L. Carter, J. Fox, J. Griffiths, and G. W. Holtgrieve. 2007. Biotic control of stream fluxes: spawning salmon drive nutrient and matter export. Ecology 88:1278–1291.
Research Publications and Presentations
Tiegs, S.D., D.T. Chaloner, P. Levi, J. Rueegg, J.L. Tank and G.A. Lamberti. 2008. Timber harvest transforms ecological roles of salmon in Southeast Alaska rain forest streams. Ecological Applications 18:4-11.
Levi, P., J. L. Tank, S.D. Tiegs, D.T. Chaloner and G.A. Lamberti.(2007, June)Influence of Forest Management on Salmon-Derived Nutrient Dynamics in Southeast Alaska Streams. North American Benthological Society, Columbia, SC,. Bulletin of the North American Benthological Society.
Tiegs, S.D., D.T. Chaloner, P. Levi, A. Reisinger, J. Rüegg, J.L. Tank and G.A. Lamberti. 2007. Historical Timber Harvest and Its Lingering Influence on the Utilization of Salmon-derived Nutrients in Stream Ecosystems. Alaska Chapter of the American Fisheries Society. Ketchikan, AK, USA. Oral Presentation.
Tiegs, S.D., D.T. Chaloner, P. Levi, J. Rüegg, J.L. Tank and G.A. Lamberti. 2007. Timber Harvest Influences the Ecological Roles of Salmon in Southeast Alaska Streams/. Pacific Salmonid Recovery Conference. Seattle, WA, USA. Oral Presentation.
Tiegs, S.D., D.T. Chaloner, P. Levi, J. Rueeg, J.L. Tank and G.A. Lamberti. (in press). Timber harvest transforms ecological roles of salmon in Southeast Alaska rainforest streams. Ecological Applications.