Can aquatic plant removal increase nighttime oxygen in a lowland river?
The aquatic plant water stargrass (Heteranthera dubia) dominates the lower Yakima River in Washington State and causes serious problems for the aquatic ecosystem. Its nighttime respiration drives low nighttime oxygen concentrations that are insufficient for migrating salmon (Oncorhynchus spp.). I worked with partners at the Benton Conservation District and Yakama Nation Fisheries to investigate whether plant removal would increase nighttime oxygen concentrations. Plant removal in a free-flowing river section resulted in a small but measurable increase in nighttime oxygen but had no effect in a dammed section where a smaller proportion of plants were removed. I also investigated the effects of a flow-driven plant removal. In 2022, the Yakima River experienced abnormally late-spring high flows that suppressed water stargrass growth in the early season, and nighttime oxygen that year was higher than in any previous year until plants regrew. My research suggests mechanical plant removal can be effective, but only if a sufficient proportion of plants are removed. However, flow-driven plant removal can remove plants across a much larger area and may therefore be more effective. Intentional water releases from reservoirs could possibly be used to create these flows and improve river conditions for salmon.
Aaron Pelly is a Ph.D. candidate in Environmental and Natural Resource Sciences at WSU, where he previously earned an MS and a BS in the same field. Aaron’s research interests focus on the intersection of basic science and conservation, especially how science can inform and improve management practices.