Removing the Compost Heaps: Water Quality Drivers of Food Web and Salmon Disease Risk Responses with the World's Largest Dam Removal on the Klamath River.

By a number of measures, the removal of four dams on the Klamath River, scheduled to occur in January 2024, is the world's largest river restoration project. It is also among the world's most rapid, dramatic, and best documented change in water quality. The reservoirs seasonally store and release nitrogen and phosphorus delivered from upstream, as well as host substantial cyanobacterial blooms during the summer and contribute to disease risk from the pathogen Ceratanova Shasta (C. Shasta). Removing the dams will produce a pulse release of stored nutrients and organic sediments (i.e. algae) and increase long-term nutrient delivery via removal of the nutrient traps. This presentation will synthesize existing and new data and knowledge about the current reservoir and river water quality and their interactions with the food web, with emphasis on toxic cyanobacteria and on the invertebrate worm that hosts C. Shasta. The presentation will also: 1) include detailed hypotheses about what the water quality, food web, and disease risk may look like post dam removal, 2) summarize the next four years of study to occur during dam removal, including work with the Tribes to document Indigenous knowledge about water quality, and 3) synthesize how water quality-food web interactions on the Klamath are relevant to other rivers experiencing nutrients changes from changing climate, wildfire severity, and land use.