Select Page
harmful algal blooms

A bloom of blue-green algae on Florida’s Lake Okeechobee is visible from space.

Toxic algae blooms, which occur worldwide, have been making headlines from coast to coast in the United States. Florida and California are seeing blooms now and face more in the future.

What conditions trigger these blooms? There are at least 400 coastal zones in the world that are hypoxic, meaning the available oxygen in the water is low, which makes them prime spots for algal blooms. Add warm, sunny days to these nutrient-rich waters, and the algae go wild.

Algal blooms are sometimes known as red tide because some phytoplankton appear to turn water red when they bloom. Many scientists use the term “harmful algal blooms,” in part because some algae don’t discolor the water, even though they may secrete toxins and otherwise pollute the water.

Eutrophication and Algal Blooms

When fresh water is too rich with nutrients — called eutrophication — it becomes a breeding ground for algae. The nutrients include naturally occurring nitrates and phosphates, or those introduced by fertilizer runoff or sewage discharge. This can be resolved thorough better wastewater treatment, which reduces the amount of nutrients entering waterways, as well as stringent pollution controls.

Rhea Shu, president of the Natural Resources Defense Council, explained on AlterNet:

The immediate cause of the blooms can vary, but the common basics are these: Rains wash pollution from farms, septic tanks and other sources into our waters — from small streams and wetlands to great rivers and lakes — and municipal sewage systems add waste to these waters. These pollutants then supercharge the waters with nutrients like nitrogen and phosphorus. That feeds a population explosion for algae that feast on these nutrients. Warmer temperatures accelerate the growth.

Recent Algal Blooms

The Great Lakes region has been the site of numerous recent outbreaks, and they are a frequent occurrence at the mouth of the Mississippi River. In California, a combination of warm temperatures, calm conditions, and bright sun in mid-July triggered a blue-green algal bloom in lakes including Pyramid Lake.

Blue-green and brown algae rapidly grew unchecked in Florida as the result of nutrient-rich drainage from Lake Okeechobee and stormwater runoff. The guacamole-thick matted algae bloom was 33 miles wide and could be seen from space, according to NASA.

Triggering Algal Blooms

Newer research has found that carbon dioxide has a role in triggering algal blooms. The algae need carbon dioxide for photosynthesis and growth. When algae bloom, they deplete dissolved carbon dioxide in the water. With greater carbon dioxide in the atmosphere, there is greater carbon dioxide in lakes and other surface waters. This availability of carbon dioxide delays depletion of the dissolved carbon dioxide in water, enabling algae to grow and establish dense populations. The problem intensifies in waters with high levels of nitrogen and phosphorous present.

One of the big problems worldwide is phosphorous pollution. The journal Water Research, which had a special issue on the topic, stated:

Phosphorus is the biggest cause of water quality degradation worldwide, causing ‘dead zones,’ toxic algal blooms, loss of biodiversity and increased health risks for the plants, animals and humans that come in contact with polluted waters. […] The scale of the problem is daunting, and despite major attempts to reduce the runoff, human activities are still pumping 10 million tonnes of extra phosphorus into freshwater sources every year.

Algae and Water Treatment

Once these harmful algal blooms occur, they become a prime concern in water quality management. They can lead to closure of recreational waters — which occurred in Florida at the height of the traditionally busy Fourth of July weekend — and can cause health problems — some fatal — to humans and other mammals.

The blooms also cause problems for water treatment and desalination facilities. They occur on the water’s surface, but the biomass can migrate throughout a water column, which means it’s hard to avoid them even with deeper water intakes. This can cause problems such as membrane clogging for desalination operators.

Water treatment to reduce nitrogen and phosphorous is an important means to reduce nutrients in the water. Runoff pollution from other sources also needs to be monitored to help protect surface water sources and aquatic life, researchers say. Bringing conditions back into balance can’t happen quickly or easily.

Bill Mitsch, director of the Everglades Wetland Research Park at Florida Gulf Coast University, told Circle of Blue:

What’s going on in Florida, it’s happening all around the world now. There are too many people, too much food production, too much fertilizer on the landscape. It’s going to be haunting us for a long time. […] It’s a hydrological mess right now, but it’s not unsolvable.

Image by Joshua Stevens, courtesy NASA.

Connect with Fluence

Sign up for the latest news, trends and innovations in water, wastewater and reuse.

  • This field is for validation purposes and should be left unchanged.