Marine Derived Nutrients Water Chemistry Data, Kenai Penninsula, Alaska (2004-2006)

MDN and delivered by salmon and other anadromous fishes are considered important drivers in riverine ecosystems, providing nutrients and food to these land-based food webs. However, we know little about the relative value of MDN compared to other nutrient and carbon sources (e.g., watershed-derived) in the Gulf of Alaska region. The objectives of this study were to develop a water chemistry proxy for monitoring salmon returns, and to track and measure MDN effects in stream, riparian and nearshore environments, on the southern Kenai Peninsula. We show that stable isotopes and fatty acids were both effective indicators of MDN assimilation in stream resident fishes. Our water nutrient profiles suggest rapid nitrogen (N) uptake in Homer streams, which have underlying phosphorous (P) rich geology. Stable isotopes were most effective when the salmon-free end member was relatively depleted. Marine-derived nitrogen (deltaN15) was highly variable, likely due to spatial variation in N sources and cycling, and may not be a reliable predictor of MDN inputs at the watershed scale. Fatty acids were most effective when quantified as ω3:ω6. Based on our data the development of a nutrient proxy for estimating salmon escapement shows some promise in certain situations, but is unlikely in the majority of salmon streams in southcentral Alaska.

Walker, C.M., D. Rinella, M.S. Wipfli and C.S. Stricker. 2007. Presence and Effects of Marine Derived Nutrients (MDN) in Stream, Riparian and Nearshore Ecosystems on Southern Kenai Peninsula, Alaska: Developing Monitoring Tools for Tracking MDN in Alaska Watersheds. Exxon Valdex Oil Spill Trustee Council Gulf Ecosystem Monitoring Program Final Report (Project Number 040726).