Collaborative Research: Leaky Rivers: Nutrient Retention and Productivity in Rocky Mountain Streams Under Alternative Stable States

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Streams occupy a small part of Earth's surface, but are disproportionately important for transport and processing of nutrients and for maintaining global biodiversity. Logjams in streams increase retention of nutrients and fish production. Human removal of logjams is pervasive in forested ecosystems, creating "dam-impoverished" streams with limited capacity to store nutrients and produce fish. A prime example is streams of the southern Rocky Mountains, where a legacy of wood removal has greatly reduced logjams. This project asks: Does the loss of jams reduce the productive capacity of headwater streams? It is hypothesized that the loss of jams makes streams more leaky of nutrients, with subsequent decreased nutrient processing and fish production. This project will examine logjams and jam-associated processes across a gradient of streams, including streams in old-growth forests, unmanaged younger forests, and intensively managed forests. This work will provide the first landscape-scale assessment of the effects of jam removal on stream ecosystems. This research can transform current understanding of wood effects on stream ecosystems by combining estimates of logjam historical distribution with intensively measured geochemical and biological variables in contemporary jams, allowing extension of local-scale observations to entire steam networks. Understanding how the loss of jams affects streams will inform resource management of headwater streams in forested landscapes. The National Park Service and the US Forest Service oversee vast tracts of forested lands in the American West and are attempting to restore some of the inferred historical characteristics of the Rocky Mountain landscape. By enhancing understanding of changes in jams, as well as the biogeochemical and ecological influence of these structures, the proposed work will provide much-needed context for these management actions. This project will also provide training for one post-doctoral scholar and four graduate students. It will also provide research experiences for several undergraduate students.