by Ryan van goethem, CLM (EUTROPHIX)
Background
Map of Moses Lake with project areas highlighted in blue
Moses Lake is a 6,800-acre lake that has experienced poor water quality and harmful algae blooms (HABs) dating back to the 1960s. Previous efforts to improve water quality included diverting wastewater in the 1980s and decades of routing low-phosphorus Columbia River Water through the lake to dilute excess nutrients (Welch & Brattebo 2024). Yet in recent years HABs continue to occur across the lake.
Studies have determined that Moses Lake suffers from excess internal cycling of phosphorus (P) from lake sediments and inputs from watershed sources (Caroll 2006, Brattebo & Welch 2022). The northern part of Moses Lake (i.e., Rocky Ford Arm) does not receive the full benefit of dilution as lower Moses Lake does, allowing for higher concentrations of nutrients driving high HAB growth. Mitigating these phosphorus sources would further lower P levels, allowing for more years and longer summers without HAB blooms and advisories.
Columbia Basin Conservation District received funding to perform a large phosphorus mitigation demonstration project. EutroPHIX and Aquatechnex implemented this work on Rocky Ford Arm and Rocky Ford Creek using novel technologies for assessment and phosphorus mitigation in 2024 and into 2025.
A mobile SATT system was deployed on Rocky Ford Creek to monitor phosphorus concentrations and dose EutroSORB WC to mitigate phosphorus.
Inflow P Mitigation
Rocky Ford Creek is a major external load for the Rocky Ford Arm of Moses Lake, with stable flows recently ranging from 25-100 CFS, total phosphorus 100-300 ug/L, ortho-phosphorus 60-180 ug/L. The high concentration of ortho-phosphorus is concerning as it is a readily available nutrient for algae or HABs in lakes. To mitigate this inflowing ortho-phosphorus, a mobile SePRO Automated Treatment Technology (SATT™) system was deployed. SATT systems allow for the precise mitigation of phosphorus across a variety of conditions in flowing waters. This unit provides real-time phosphorus measurements of total phosphorus and ortho-phosphorus every four hours and includes an automated injection system to apply EutroSORB WC based on P concentrations and flow. EutroSORB® WC is a new high-efficiency liquid phosphorus binder that will bind available ortho-phosphorus into a tightly bound mineral form that settles into lake sediments. Mitigation of inflowing P was performed in the summer of 2024 and continued in spring 2025. The amount of EutroSORB WC applied will permanently bind up to 4,400 lbs. of P. Use of EutroSORB WC was permitted using Experiment Phosphorus Sequestration Project Plans approved by Washington Department of Ecology.
Lake Sediment P Mitigation
Aquatechnex crew poured 50 lb. bags EutroSORB G as a dry granule into the application equipment at Moses Lake to create a EutroSORB G slurry (left). Application boats applied the EutroSORB G slurry in a fan pattern across a 40-50 foot swath where it settled to the lake bottom (right).
Phosphorus budgets for Moses Lake indicate that about half of the P during the summer is from internal loading of P (Brattebo & Welch 2022), with a portion of this occurring in Rocky Ford Arm. A detailed assessment of lake sediments in Rocky Ford Arm was performed October 2024 to help plan phosphorus mitigation. These data highlighted high concentrations of mobile sediment P downstream of Rocky Ford Creek and in the deeper areas of Rocky Ford Arm (170-310 mg-P/kg). A new lanthanum-modified bentonite formulation called EutroSORB® G was used to sequester mobile phosphorus in the sediments. EutroSORB G has 10% lanthanum embedded inside a clay matrix (90%). This product disperses and sinks through the water column, rapidly binding ortho-phosphorus, then settles on the bottom. Available binding sites will continue to bind phosphorus released from the sediments and incorporate into the sediment over time. EutroSORB G-bound phosphorus transitions to a stable mineral, monazite (LaPO4), which is essentially permanent and non-bioavailable under typical environmental conditions. In June 2024, 250 tons of EutroSORB G were applied to 2,083 acres of the Rocky Ford Arm using multiple application boats. This application was a partial treatment dose (~16% of total) compared to mobile sediment P available and will permanently bind up to 10,000 lbs. of P.
Results
In 2024, EutroPHIX implemented a comprehensive monitoring program on Moses Lake to track the changes in water quality from phosphorus mitigation treatments. Initial monitoring results demonstrate significant improvements in the water quality of Moses Lake over 2024. The injection of EutroSORB WC in Rocky Ford Creek reduced soluble-reactive phosphorus 40% (on average) while in operation. After the application of EutroSORB G, total phosphorus declined steadily in the bottom waters by >32% to September. Total phosphorus in the surface water for the middle of Rocky Ford Arm averaged 35.4 µg/L for the summer, but without treatment was expected to be approximately twice as high due to the lack of Columbia River Water dilution in Rocky Ford Arm for 2024. Sediment analysis indicates that the mobile P in surficial sediments (4cm) decreased by ~26% by October 2024. Most of the algae biovolume in the summer was dominated by beneficial green algae and diatoms, while cyanobacteria had dominated historically. Additional inflow P mitigation work will continue in 2025 to complete the project, and the results will guide further planning for water quality improvement. Further data analysis will be performed and presented at the 2025 WALPA conference.
A video of the project being implemented is available at: https://eutrophix.com/case-studies-news/
References:
Welch, E. B., & Brattebo, S. K. (2024). Effectiveness of diluting Moses Lake, Washington, with low phosphorus Columbia River water. Lake and Reservoir Management, 40(4), 339–353. https://doi.org/10.1080/10402381.2024.2404582
Carroll, J. (2006). Moses Lake Phosphorus-Response Model and Recommendations to Reduce Phosphorus Loading. www.ecy.wa.gov/biblio/0603011.html
Brattebo, S., & Welch, E. (2022). Moses Lake – Whole Lake Mass Balance Model & Management Alternatives Evaluation. https://mlird.org/cleanlakeproject.html
