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Storms and pH of dam releases affect downstream phosphorus cycling in an arid regulated river

July 6, 2023

Reservoirs often bury phosphorus (P), leading to seasonal or persistent reductions in P supply to downstream rivers. Here we ask if observed variation in the chemistry of dam release waters stimulates downstream sediment P release and biological activity in an arid, oligotrophic system, the Colorado River below Lake Powell, Arizona, USA. We use bottle incubations to simulate a range of observed pH (6–8.8) and oxygen (0–9.4 mg L−1) levels, with the hypothesis that either oxygen concentrations or pH regulates P release from sediments to the water column. We found support for pH-mediated P release from calcite across the three sites we sampled. The magnitude of this effect was lower in bottles filled with tailwater sediment, but at downriver sites low pH resulted in declining water column dissolved inorganic nitrogen:soluble reactive P (DIN:SRP) ratios, which dropped below the Redfield ratio of 16:1, increasing water column total protein production, and down-regulating alkaline phosphatase production. Additional 7-day incubations showed that tributary storm inputs can temporarily elevate riverine P availability from < 1.5 µg L−1 total dissolved P (TDP) pre-storm to 6.7 µg L−1 TDP post storm. Taken together, our lab incubation and long-term observational results highlight the importance of pH, and ultimately reservoir management and storm dynamics, in regulating P availability and biological processes both now and into the future.

Publication Year 2023
Title Storms and pH of dam releases affect downstream phosphorus cycling in an arid regulated river
DOI 10.1007/s10533-023-01064-5
Authors Bridget Deemer, Robin H. Reibold, Anna Fatta, Jessica R. Corman, Charles Yackulic, Sasha C. Reed
Publication Type Article
Publication Subtype Journal Article
Series Title Biogeochemistry
Index ID 70246677
Record Source USGS Publications Warehouse
USGS Organization Southwest Biological Science Center