UC Davis proposes hypolimnetic oxygenation pilot for Clear Lake to curb internal phosphorus loading
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Summary
UC Davis researchers outlined a three-year pilot to inject oxygen into Clear Lake bottom waters to reduce internal phosphorus release, targeting the Oaks Arm as a demonstration to lower risks of harmful algal blooms; board members pressed on permitting, costs and how a pilot would be sustained after grant funding ends.
Researchers from UC Davis told the Board that internal loading from lakebed sediments drives roughly 70% of the phosphorus that fuels summer algal blooms in Clear Lake. To reduce that source, the team proposed a hypolimnetic oxygenation system (HOS) pilot in the Oaks Arm for up to three years aimed at keeping bottom waters oxygenated to prevent phosphorus release.
"You basically want to prevent this internal loading from happening," said Alex Forrest, associate director at the Tahoe Environmental Research Center. The plan calls for oxygen injection lines and a distributed array of observation buoys, coupled with USGS monitoring to track nutrient and oxygen dynamics. Researchers said they were seeking necessary permits and hoped for operation this summer, but acknowledged fallback planning if permitting or design issues delay deployment.
Board members raised financial sustainability concerns if the pilot shows promise and the three‑year grant ends. An expert said a CEQA exemption for limited-duration science projects was anticipated, and that a local water district could be a potential operator after the pilot period. Staff estimated ongoing annual operating estimates would depend on oxygen demand (rough projected annual operation cost ballpark $500,000–$600,000 based on early engineering), with uncertainties to be resolved by bids and pilot monitoring outputs.