Theme: 14. Emerging Contaminants

Topic Area: 14f. Microplastics, Pharmaceuticals, and Other Emerging Contaminants

Formatted Title:

Evaluation of Aluminum Sulfate (“Alum”) Dosing to Remediate Harmful Algal Blooms in Reservoirs

Background/Objectives:

Eutrophication and harmful algal blooms (HABs) continue to plague the ecological health and community enjoyment of global freshwater and coastal ecosystems. As urban and agricultural nutrient loading continues, and climate change-induced hydrology and meteorology changes increase, preventing the eutrophication of water bodies will become a high priority project for many municipalities that rely on these reservoirs for drinking water, recreation, fishing, and tourism. Improvements to instrumentation and HABs treatment technologies have allowed some water body managers to achieve success in managing and mitigating eutrophication and HABs. The use of aluminum sulfate ("alum") for nutrient inactivation has shown promise in water bodies where comprehensive assessments indicate that HABs are primarily driven by internal phosphorus loading from the sediments.

Approach/Activities:

At Moswansicut Reservoir, a 286-acre reservoir located in Johnston and Scituate, Rhode Island (RI), 70,359 gallons of alum and 34,824 gallons of sodium aluminate were injected below the water’s surface by a treatment vessel over the course of seven days. The target treatment area was 173 acres, including the area of maximum depth (47 feet deep) and adjacent shallower areas (approximately 20 feet deep). To measure and quantify success of this treatment, a specialized water quality buoy was deployed at the surface in the area of maximum depth of the reservoir to allow for real-time monitoring of dissolved oxygen (DO), temperature, turbidity, chlorophyll-a, pH, and blue-green algae levels within the water body.

Results/Lessons Learned:

Prior to treatment, chlorophyll levels were measured as high as 32 µg/L and the reservoir was experiencing recurring HABs that were inconsistent with its designated use as a public water supply reservoir. Since treatment, Moswansicut Reservoir has not experienced an observable HAB, and the chlorophyll levels remain consistently below 5 µg/L during peak HAB season (July – October). Readings of DO, temperature, turbidity, chlorophyll-a, pH, and blue-green algae levels from Moswansicut Reservoir’s cellular data buoy provide real-time, high-frequency data to evaluate hydrological and ecological patterns and alert water body managers to conditions favorable to accelerated algal growth. Lessons learned from design and implementation will be discussed, as well as an evaluation of more than 5 years of post-treatment monitoring data.

Menu

Matthew Ladewig