Nutrient pollution

Nutrient pollution is a form of water pollution caused by too many nutrients entering the water. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farms, waste from septic tanks and feedlots, and emissions from burning fuels. Raw sewage, which is rich in nutrients, also contributes to the issue when dumped in water bodies. Excess nitrogen causes environmental problems such as harmful algal blooms, hypoxia, acid rain, nitrogen saturation in forests, and climate change.

Agricultural production relies heavily on the use of natural and synthetic fertilizers, which often contain high levels of nitrogen, phosphorus and potassium. When nitrogen and phosphorus are not fully used by the growing plants, they can be lost from the farm fields and negatively impact air and downstream water quality. These nutrients can end up in aquatic ecosystems and contribute to increased eutrophication.

To reduce nutrient pollution, several strategies can be implemented. These include installing buffer zones of vegetation around farms or artificial wetlands to absorb excess nutrients. Additionally, better wastewater treatment and reducing sewage dumping can help limit nutrient discharge into water systems. Finally, countries can create a permit system under the polluter pays principle.

The principal source(s) of nutrient pollution in an individual watershed depend on the prevailing land uses. The sources may be point sources, nonpoint sources, or both:

Nutrient pollution from some air pollution sources may occur independently of the local land uses, due to long-range transport of air pollutants from distant sources.

In order to gauge how to best prevent eutrophication from occurring, specific sources that contribute to nutrient loading must be identified. There are two common sources of nutrients and organic matter: point and nonpoint sources.

Use of synthetic fertilizers, burning of fossil fuels, and agricultural animal production, especially concentrated animal feeding operations (CAFO), have added large quantities of reactive nitrogen to the biosphere. Globally, nitrogen balances are quite inefficiently distributed with some countries having surpluses and others deficits, causing especially a range of environmental issues in the former. For most countries around the world, the trade-off between closing yield gaps and mitigating nitrogen pollution is small or non-existent.

Phosphorus pollution is caused by excessive use of fertilizers and manure, particularly when compounded by soil erosion. In the European Union, it is estimated that we may lose more than 100,000 tonnes of Phosphorus to water bodies and lakes due to water erosion. Phosphorus is also discharged by municipal sewage treatment plants and some industries.