For water treatment operators and utility officials, the summer months don’t just mean sunshine, pool parties, and barbecues. The season also brings the peak time for algal blooms, the toxic clouds formed in surface water thanks to increased nutrient contamination and rising temperatures. With rising instances of toxic algae around the country and increased regulations for eliminating it, utilities have had to keep pace.

To learn more about blooms and solicit advice for utilities that have to combat algae, Water Online spoke with Harmsco Filtration Products. We got the lowdown on the invasive guest, lessons from the outbreak in Toledo, OH, and how different areas should handle their own unique algae challenges.

What causes the formation of toxic algae in surface water?

The development of algal blooms can be caused by a number of environmental factors, such as nutrients (nitrogen and phosphorus), temperature, sunlight, hydrology (slow-moving water), and water chemistry (pH and carbon availability).

Nutrients promote and support the growth of algae and cyanobacteria. Runoff from fertilizer used in agriculture and lawns are generally the major source of phosphorus and nitrogen in waterways.

Water temperatures above 77°F are optimal for the growth of blue-green algae. At this temperature, blue-green algae have an advantage over other types of algae, which prefer temperatures of 55°F to 60°F. Also, the density of water is influenced by the temperature — surface waters are usually warmer and less dense than bottom waters, which are usually cooler and denser. Warming waters can increase thermal stratification due to the warming surface water, creating a physical force that can resist the wind’s ability to mix the water. This can develop a layer that resists vertical movement of oxygen and nutrients, which favor the growth of harmful algal blooms.

Are there geographical areas that are more susceptible to algal blooms than others?

Harmful algal blooms occur in almost every U.S. coastal state, including the Gulf of Maine through the Gulf of Mexico and as far north as Alaska.

What active steps should a utility take if threatened with toxic algae in nearby surface waters?

It is important that utilities have a monitoring plan which includes when and where to sample, sample frequency, sample volume, test protocols to use, and when it may be necessary to send samples to labs qualified for testing.

When a utility is threatened with an algal bloom, they should be cautious in pretreatment before filtration. The cyanotoxins can be removed with filtration as long as they are intracellular, meaning the cells are still intact. Pretreatment oxidation can lyse cyanobacteria cells, releasing the cyanotoxins into the water. Extracellular cyanotoxin removal can be achieved by additional treatment practices, such as use of membranes, filtration, potassium permanganate, ozone, chlorine, and activated carbon. The effectiveness of these treatments can vary depending on the water chemistry, including the pH levels, amount of organic matter, and temperature.

There are also other operating strategies that may be available to deal with the blooms. If the utility has access to more than one intake, they could switch to an alternate that may not be as greatly impacted. The intake depth may also be adjusted, which could reduce the exposure of contaminated water into the treatment plant.

What has been the lasting impact, if any, from the Toledo, OH, cyanobacteria water shutdown in 2014?

Since the water shutdown, there has been a significant increase in research in many different areas, concerning such subjects as how much nitrogen and phosphorus levels need to be decreased in Lake Erie, identifying microcystin-degrading bacteria, and the use of activated carbon for the removal of cyanotoxins

They are also testing toxin levels in Lake Erie for walleye and yellow perch. Some lab testing has shown that vegetables can accumulate microcystin if water used to irrigate them contains the toxins. The research has also indicated that using affected water in agriculture can slow the growth of the crops.

Do you believe these outbreaks will continue to rise? Or is there reason to believe they will stay the same or subside?

There are documented cases of algae blooms in Florida’s coastal water as early as the 19th century. Therefore, they are not a new phenomenon, but the increase in nutrients in waterways has contributed to increased blooms in freshwater systems.

Over the last few years, the reports of widespread algal blooms in Lake Erie have included both the shutdown of the drinking water treatment plant in 2014 and a record-breaking bloom in 2015. Last summer, Minnesota had blooms reported in lakes across the state from the Iowa border all the way to the Canadian border. There were reports of human illness as well as multiple dog deaths. Due in part to the mild spring this year, there were already reports of blooms on Memorial Day weekend.

Scientists anticipate that climate change might cause algal blooms to occur more often, in more locations, and more intensely. Climate impacts that could affect algal blooms include warming water temperature, changes in water salinity, higher carbon dioxide levels, changing rainfall patterns, rising sea levels, and coastal upwelling.

Image credit: “Algal Bloom” eutrophication&hypoxia © 2006, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by-nc/2.0/