Thursday, August 6, 2009 - 4:20 PM

COS 101-9: Assessing the impact of changing climate and geomorphology on lake thermal regimes in a sockeye salmon watershed

Jennifer R. Grififths, Daniel E. Schindler, and Laurie S. Balistrieri. University of Washington

Research investigating the effects of climate change on freshwater species and ecosystems frequently assumes a static landscape. Yet landscapes are dynamic and, especially in areas of recent glacial and volcanic activity, can evolve on temporal scales relevant for understanding ecosystem responses to global change. On the Alaska Peninsula, climate warming is occurring simultaneously with rapid geomorphic evolution of the upper Chignik watershed, which has substantially altered rearing habitat for juvenile sockeye salmon (Oncorhynchus nerka). A large, shallow, isothermal lake has lost 23% of its volume since 1960 and volume continues to decline. Fry emigrating during mid-summer have shown evidence of thermal stress and overwintering life histories strategies have changed. We used a hydrodynamics model to assess whether further volume loss can lead to a substantial shift in lake thermal regimes. We investigated the effects of two potential restoration strategies for improving sockeye salmon rearing habitat: an outlet control structure and a tributary diversion. Additionally, we assessed the potential efficacy of these restoration strategies given projections of future climate regimes.

Model simulations demonstrate that a decline in maximum depth alters the lake thermal environment by increasing the magnitude of cooling periods. If a decline in lake volume also decreases connectivity to some lake tributaries, there is an overall increase in stressful thermal conditions for juvenile sockeye. However, a river diversion strategy maintains tributary connectivity and results in cooler lake temperatures as volume declines.  Alternatively, restoration to restore historic water levels using an outlet control structure will not decrease summer thermal stress for juvenile sockeye salmon under current climate conditions. The restoration consequences for lake thermal regimes under future climate are quite different.  There are large magnitude effects of predicted air temperature increases on lake temperatures leading to a more stressful thermal rearing environment for juvenile sockeye salmon. Neither restoration strategy is likely to mitigate lake temperature response to increasing air temperatures. Rapid landscape evolution has the potential to amplify or dampen the response of ecosystems to climate change. Our understanding of ecosystem responses to climate change and the creation of successful management strategies may be enhanced by considering the role of landscape evolution.