Using GIS to identify hotspots of salmon-derived nutrient influence in managed watersheds of Southeast Alaska
Janine Rüegg, Dominic T. Chaloner, Scott D. Tiegs, and Gary A. Lamberti. Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556
Pacific salmon are believed to be an important source of nutrients for freshwater and terrestrial ecosystems. The influence of salmon-derived nutrients (SDN) on ecosystems is determined by the extent of resource input, retention, and uptake, all of which vary across the landscape, both within and among watersheds. Our objective was to assess the prevalence of ‘hotspots’ where the influence of SDN is especially pronounced. Field data and published results were used in Geographic Information Systems (GIS) analyses to identify hotspots in riparian and instream areas of watersheds on Prince of Wales Island, Southeast Alaska. Qualifying criteria include soil type (Tuxekan and Tonowek; measured range, 1–6% of watershed area), stream channel type (floodplain; 3–9% of stream length), and lateral SDN transfer distance from exploited stream channels (500 m buffer; 10–32% of watershed area). Using these criteria, less than 3% of the area of the watersheds studied are hotspots of SDN influence. Timber harvest can restrict this area even further (6–95% depending on harvest intensity) because of likely impacts of disturbance on landscape criteria. Hotspots of SDN influence may coincide with the location of previous studies, thereby overestimating the importance of SDN at the watershed scale.