The Influence of Marine-Derived Nutrient Subsidies on Streams and Lakes at Izembek National Wildlife Refuge

Although the effects of Pacific salmon spawners have been well-studied in the Pacific Northwest, their influence remains relatively unexplored across portions of their range including the North Pacific Rim and along the Alaska Peninsula. In my first data chapter, I examined whether the influence of salmon on streams and lakes at Izembek National Wildlife Refuge (INWR) was similar to previously studied salmon-bearing ecosystems. At INWR, the impact of salmon was smaller than elsewhere, likely due to small run sizes and regional environmental characteristics including very low background molar nitrogen to phosphorous ratios. Nevertheless, I found that upstream and downstream reaches within a single watershed can respond differently to salmon migration, suggesting that salmon differentially influence freshwater ecosystems depending on landscape position. In my second data chapter, I examined whether marine-derived nutrient subsidies from salmon and waterbirds differ in their effects on lake ecosystems. In general, lakes receiving subsidies had higher nutrient concentrations than lakes with no significant subsidies, and water column chl-a was positively correlated to nutrient availability. However, biofilm nutrient limitation differed between lakes receiving salmon versus waterbird subsidies. In summary, both source and environmental context strongly influences the effect of marine-derived nutrient subsidies in streams and lakes at INWR.