Effects of Anadromous Salmon on North Shore Stream Ecosystems

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For streams on the North Shore of Lake Superior, salmon are a recently introduced exotic species, and may be altering the stream ecosystems from their historic state. Are salmon migrations into streams a significant source of nutrients and high quality organic matter for these stream ecosystems? The importance of migration salmon in nutrient and organic matter flow through stream ecosystem components will be tested using experimental, comparative, and stable isotope tracer techniques. It is hypothesized that the presence of salmon will: 1) result in a shift away from terrestrial sources of organic matter and inorganic nutrients toward lake derived sources (salmon carcasses and spawn); and 2) will alter the seasonal patterns of nutrient limitation. This shift will be reflected in changes in periphyton, fine particle and dissolved organic carbon, grazer, shredder, and collector components of the ecosystem which can be traced using stable isotopes. It is further hypothesized that, 3) the size of a patch of salmon carcasses determines the spatial scale of the effect on the resource within the ecosystem. A combination of experimental and comparative studies will provide insight into the interdependence of nutrient limitation and nutrient and organic matter flow through these stream ecosystems.