Can ‘Capturing’ Phosphorus Reduce Blooms? | Ohio Sea Grant

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Can ‘Capturing’ Phosphorus Reduce Blooms?

12:00 pm, Sun April 28, 2024 – Researchers with the Harmful Algal Bloom Research Initiative (HABRI) explored new potential methods to “capture” phosphorus released from cyanobacteria without harming ecosystems

Each summer, drinking water reservoirs in Ohio face potential risks to human health from harmful algal blooms. As water temperatures rise, excess nutrients — such as phosphorus — cause photosynthetic, blue-green cyanobacteria to grow rapidly, releasing toxins.

To help water utilities be proactive in reducing blooms, researchers with the Ohio Department of Higher Education’s Harmful Algal Bloom Research Initiative (HABRI) recently explored new potential methods to “capture” phosphorus released from cyanobacteria without harming other microorganisms and the ecosystem at large.

The project, led by Dr. Teresa Cutright, professor of civil engineering at The University of Akron, measured the success of using a new phosphorus-binding product in tandem with the hydrogen peroxide-based algaecide PAK-27. Results showed that the applications were promising, with limitations over time and depending on conditions of the water.

a person holds a net on a boat alongside several buckets

Researchers collected water samples and cyanobacteria from northeast Ohio drinking water reservoirs — including Mosquito Creek Lake in Trumbull County, pictured here — to study the effects of applying a phosphorus-binding product alongside a peroxide-based algaecide.

“We don’t want to completely get rid of these organisms because they produce oxygen, and cyanobacteria actually produces more oxygen than most trees. It’s essential for human beings,” Cutright said. “But for any living system, it’s always a question of how much and are things in good balance.”

Cutright’s research focuses on controlling the impact of algal blooms by treating the problem in reservoirs using chemical additions, such as algaecides. Historically, water resource managers relied on Copper-based algaecides, which can kill off non-target organisms and leave residual elemental copper in the water — to be removed later by a water treatment plant.

More recently, however, hydrogen peroxide-based algaecides have proven to be more selective toward cyanobacteria, leaving other photosynthetic organisms such as green algae and diatoms alone, Cutright said. If the cyanobacteria are ‘damaged’ instead of killed, it limits the amount of toxins released at one time. And when the algaecide breaks down, it doesn’t leave any residuals that have to be treated.

“It can be a little more expensive, but in the long run it can be more beneficial for the ecosystem,” Cutright said. “We want to have the healthiest water bodies with a whole community of organisms thriving together.”

The latest project came about after an algaecide manufacturer claimed that a phosphorus-binding product, Phoslock®, could be applied in a reservoir treated with PAK-27 and hold onto phosphorus released by cyanobacteria forever. Cutright’s team aimed to test this claim and see whether the combined approach could be practical for reservoir managers. Phoslock®, a bentonite clay adapted to contain the rare element lanthanum, can temporarily adsorb — take up and hold — phosphorus, similar to how a paper towel will adsorb a liquid but release it if squeezed, Cutright explained.

For the experiment, researchers applied PAK-27 at a full dose recommended by the manufacturer and a quarter dose at three different northeast Ohio reservoirs. Then, 24 hours after each application, they applied the Phoslock® at a ratio of 200 pounds per every one pound of phosphorus. Purchasing the material and paying workers to go out on boats to apply it over a small area is expensive, Cutright said.

““It can be a little more expensive, but in the long run it can be more beneficial for the ecosystem. We want to have the healthiest water bodies with a whole community of organisms thriving together.””
Dr. Teresa Cutright

“Most water utilities and personnel will say that if they’ve got something that can provide a healthy ecosystem that’s going to last for a long period of time, but it has a large upfront cost, they’ll figure out a way to do it,” Cutright said. “We want to make sure it’s worth the money that they’re spending. Does this product deliver what it says, and if so, for how long?”

Researchers sampled water and cyanobacteria at each reservoir, tracking levels of cyanobacteria and non-target organisms over time. They also conducted experiments applying Phoslock® to jars of water under different conditions — with and without sediment, in the presence and absence of oxygen — over 18 months to see how much phosphorus would be adsorbed (held) or desorbed (released) over time.

“Depending on what’s in the water, it might release phosphorus more or hold onto it more,” Cutright said.

Ultimately, the team found that PAK-27 was effective at controlling a bloom, even at a quarter dose, depending on the watershed and what organisms were present, Cutright said. They also found that the Phoslock® did its intended job, binding the phosphorus released by cyanobacteria.

However, under certain conditions, applying PAK-27 alone led to the same phosphorus level within the two-week experiment, and the desorption experiments showed that the Phoslock® would release phosphorus over time.

“So it wouldn’t be a one and done, one-time application. You would have to repeat the applications,” Cutright said.

In addition, when sediment was present, the amount of phosphorus in the water would increase over time, depending on if system was aerobic or anaerobic. This phosphorus may have previously been bound by the Phoslock®, or it was released from sediment that was holding onto legacy phosphorus for decades, Cutright said. Researchers also found evidence suggesting that iron levels in the water will impact the effectiveness of the application.

Cutright said her biggest concern with Phoslock® is the expense to apply it in large quantities over small areas, so it might not make sense for very large reservoirs or water utilities with smaller budgets. Whether the application will work in a reservoir will depend on its water chemistry and microbial community, she said.

“If people have the time to be proactive, they might not have to put a full dose of copper-based or PAK-27 algaecide,” Cutright said. “They might be able to do a lower dose and keep an eye on things, and that could save the health of the ecosystem long-term and save lots of money for the utility.”

After the study, the team shared information with each of the water utilities that participated in the study.

“I think it went very well,” she said. “I’m very happy for HABRI and Sea Grant being around to address critical issues with water quality and access. I think it’s important to inform water utility users if a product delivers on everything that’s promised.”

Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.

ARTICLE TITLE: Can ‘Capturing’ Phosphorus Reduce Blooms? PUBLISHED: 12:00 pm, Sun April 28, 2024 | MODIFIED: 4:22 pm, Mon April 29, 2024
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