Florida in the United States of America recently declared a state of emergency as a red tide of toxic algae bloomed along its western coastline killing marine animals, disrupting tourism and causing respiratory problems.

Algal blooms, their toxic emissions and the oxygen-starved dead zones they leave in their wake are not new to Florida, nor are they specific to the United States. They are a global phenomenon, and increasingly a global problem.

Coastal algal blooms are often the result of land-based pollution, commonly associated with runoff from fertilizer applications on croplands, or emissions from livestock or human wastewater.

Inefficient use of fertilizer is a major problem: more than half of the synthetic fertilizer ever applied to the world’s fields has been applied in the past 30 years, reports environmental journalist Fred Pearce in an editorial for chinadialogue ocean. Less than half of this fertilizer reaches the crops it’s intended for. The rest runs off into the wider environment and eventually into the ocean.

“No wonder dead zones are a growing global phenomenon. More than 500 have been mapped from the East China Sea to the Baltic and the Black Sea to the Gulf of Mexico. Since 1950, their extent in coastal waters has increased tenfold , ” says Pearce.

Fertilizer contains nitrogen and phosphorus – vital elements for crops on land and for algae in water. With large influxes of these nutrients, algal blooms can become extensive, and some species – such as the one currently affecting Florida – emit harmful toxins. As they die and decompose, they starve the water of oxygen in the process, with severe impacts on aquatic life forms.

Algal blooms are a natural phenomenon. But since about the 1950s, their frequency, duration and geographical scope have increased, largely in response to fertilizer runoff and sewage discharge associated with population growth, and human-induced climate change.

Harmful blooms and climate change: is there a link?

Only a few algal blooms are toxic and long-lasting enough to kill animals and cause human health problems.

Harmful algal blooms occur when colonies of algae – simple photosynthetic organisms that live in the sea and freshwater – grow out of control in response to nutrient inputs, producing toxic or harmful effects on people, fish, shellfish, marine mammals and birds. Such blooms can also affect local and regional economies, as is happening in Florida.

Red tide events caused by blooms of the harmful algae Karenia brevis are particularly common in coastal regions of Florida and Texas. During such events, the National Oceanic and Atmospheric Administration issues twice-weekly forecasts to monitor bloom conditions and impacts. The forecasts help people make informed choices about where and when to visit areas that may be temporarily affected by a bloom.

Harmful algal blooms, known to pose risks to human and environmental health in large freshwater reservoirs and lakes, are projected to increase because of climate change, according to a team of 12 researchers from Tufts University in the United States. Warmer waters and an abundance of nutrients are likely to affect concentrations of harmful algae, the scientists’ article notes.

UN Environment nutrient pollution expert Christopher Cox agrees: “As water temperatures remain persistently warm for longer periods, the likelihood of harmful blooms becomes greater.”

Tackling excess nitrogen

UN Environment, with funding support from the Global Environment Facility, is implementing a global initiative to address excess nitrogen in the environment and its negative effects.

This project, titled Towards the Establishment of an International Nitrogen Management System, provides a global assessment of reactive nitrogen and its environmental and social impacts. It also aims to provide recommendations on strategies to reduce emissions of reactive nitrogen, including measures to make production systems, especially farms, more efficient in their use of fertilizer.

Reduction in the amount of food waste will be a critical element in reducing nitrogen and the potential environmental impacts of producing food.

“We have become increasingly aware of the plight of our oceans in the face of pollution, especially with plastics. But we must also be aware of unseen pollution from nutrients and wastewater that has just as damaging an effect on our aquatic and marine ecosystems,” says Cox.

Getting rid of harmful algal blooms

Recent research in the UK suggests that treating toxic algae in inland waterways with hydrogen peroxide can be effective in reducing fish deaths. After use, hydrogen peroxide breaks down harmlessly into water and oxygen, offering strong environmental benefits compared with some commercial algaecides.

A University of California study based on field trials in China suggests that fertilizer application rates for grain crops could be reduced by a quarter without any impact on yields.

In 2015, the Indian government implemented a national policy on coating urea, a major nitrogen fertilizer, with neem oil. This gives the fertilizer a slower release property and allows the crops a greater chance of taking up the fertilizer while reducing nutrient leaching into the natural environment.

Meanwhile in Florida, the best hope may be a hurricane to flush the bloom. “Red tide blooms have been occurring in Florida since the 1800s, but there’s still no human intervention to stop it. Particularly lethal or long-lasting blooms like this one renew calls for intensified government and scientific interventions to address the problem,” reports journalist Nicole Rodriguez in the Herald Tribune.

For further information: Christopher Cox