Phosphorus pollution poses a major threat to the world's lakes

Green algal bloom in Lake Dora, Florida
CC BY 2.0 Nara Souza

Humans dump millions of tons of phosphorus into lakes every year, and it's destroying their ecosystems.

Nutrients like phosphorus and nitrogen are necessary for plant growth, but excess nutrients in a water system can cause a dangerous form of pollution known as eutrophication. Eutrophication overstimulates the growth of algae, phytoplankton, and simple plants in lakes or coastal regions. When these organisms die and decay, they deplete oxygen levels, creating “dead zones” of hypoxic, or oxygen poor, water. Few aquatic animals can survive in these conditions, which poses a huge threat to biodiversity in aquatic ecosystems.

High nutrient levels in lakes and other bodies of water are primarily a result of human industrial practices. Discharge from sewage treatment plants and runoff from agricultural fields contaminate bodies of water with excess phosphorus, leading to eutrophication.

The following diagram shows how eutrophication affects a water system.

Diagram showing the eutrophication processPew Trusts/CC BY 2.0

Many scientists consider eutrophication to be the world's most serious water quality concern. The EPA estimates that nutrient pollution in United States lakes costs Americans $2.2 billion annually in diminished property values. Over 60% of American coastal rivers and bays have been negatively impacted by phosphorus pollution, and there are currently at least 166 coastal “dead zones” in the United States. In Europe, about 40% of lakes fail to meet the water quality targets of the EU’s Water Framework Directive, mostly due to high levels of phosphorus.

Last month, an international group of researchers released a special issue of the scientific journal Water Research that focused entirely on geo-engineering, a process that could help reduce phosphorus levels in water systems. Sixty authors from 12 countries contributed to the special issue of the journal. In a press release, the authors highlighted the importance of their research.

Phosphorus is the biggest cause of water quality degradation worldwide, causing ‘dead zones’, toxic algal blooms, a loss of biodiversity and increased health risks for the plants, animals and humans that come in contact with polluted waters. This threatens the loss of economic and social benefits from freshwaters upon which society relies.

After decades of run-off from agriculture, human sewage and industrial practices, phosphorus has been stock piled at an alarming rate in our lake bed sediments. The scale of the problem is daunting, and humans are still pumping about 10 million tonnes of extra phosphorus into our freshwaters every year. Long-term monitoring activities following the control of phosphorus sources to lakes show that plants and animals don’t recover for many years. This is because phosphorus stored in bed sediments is released back to the water column. Society then has to make a decision – either speed up recovery using geo-engineering to cap sediment phosphorus stores, or do nothing, and accept poor quality freshwaters for decades to come.


Through geo-engineering, scientists manipulate environmental processes in an effort to counteract phosphorus pollution. This is mainly achieved by depositing aluminum salts or modified clays into lakes to prevent the release of phosphorus from sediment in the lake bed. Unfortunately, geo-engineering is a costly process with unknown side effects. One of the researchers, Sara Egemose of the University of Southern Denmark, explained, "Results have not always been good. Often, lake managers use geo-engineering uncritically in lakes where the reductions in external loading of phosphorous are insufficient, or have applied too low dosage because of cost." The authors of the journal stress that more research into the process is necessary. Inaction could have disastrous results for the world's lakes.

Tags: Algae | Geoengineering | Pollution

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