O'Keefe, T.C. and R.T. Edwards. Submitted. The influence of sockeye salmon and alder on the nutrient chemistry of streams in Southwest Alaska. Ecosystems.

Abstract

Adult salmon returning from the nutrient-rich water of the North Pacific provide a potentially important nutrient subsidy to the characteristically nutrient-poor streams where they spawn and die. While evidence for the importance of these marine-derived nutrient inputs to freshwater ecosystems and the adjoining riparian zone is rapidly accumulating, and the mechanisms by which these inputs are stored and transferred are currently being investigated, few have examined the relative salmon contribution across watersheds differing in key landscape features. Here we explore the importance marine nutrient subsidies in watersheds with a range of green alder (Alnus crispa) coverage. Alder are a common component of the forests in the Pacific Northwest and through their ability to fix atmospheric nitrogen , they make a potentially important contribution to the local biologically-available nitrogen pool. We conclude that although the fish nutrient subsidy is clearly important in the region's streams, its importance relative to other inputs is highly dependent on the landscape context. In streams with a large percentage of alder in their basins salmon are a minor contribution to the nitrogen pool whereas the opposite is the case when alder coverage is low. Salmon-derived phosphorus is more consistently important, but also varies with run size. As we expand our research beyond stream-specific patterns and processes it becomes important to extend one's focus beyond the fish and their immediate consumers to develop a broader understanding of the system.