Nitrates and Phosphates: The Effects on Water Quality

Nitrates and Phosphates

Over the past 50 years, there has been a constant trend towards greater intensification and higher agricultural productivity, and this has been accompanied by a significant increase in the use of inorganic nitrogen and phosphorus in fertilisers. In recent years, in order to address the resultant excessive levels of these chemicals found in waterways and mitigate the effects on water quality, measures to reduce and control their use have been implemented.

Water Quality Problems Caused by Nitrates and Phosphates

Nitrate is vital for life and is found naturally in soil and water. It forms as part of the nitrogen cycle, which occurs when organic matter is broken down by microorganisms. Because many crop plants require large quantities of nitrogen to produce high yields, additional nitrogen in the form of fertiliser is applied to crops. Unfortunately, nitrogen is extremely soluble and can be leached into groundwater, from where it enters into watercourses. This causes a nutrient boost in the environment which can then alter the ecological balance.

In addition, high nitrate concentrations in drinking water have possible health implications for both humans and animals. Treating contaminated water to make it safe for human consumption is expensive and so prevention is preferred.

Phosphates originate from many sources, including sewage and manure, and are also found in many artificial fertilisers.

In a similar way to nitrate – although an element vital for life – excess phosphate in watercourses causes a nutrient boost which often equates to excessive algae growth. The algae may then produce toxins that adversely affect the aquatic ecosystem, reducing oxygen levels, impacting fish stocks and leading to loss of species and degradation of the waterway.

Unlike nitrate, the amount of phosphate in drinking water is not regulated, although the World Health Organisation has provided a minimum ‘safe’ level of around 5mg per litre, and levels above 100mg/l can affect processes in water treatment works.

Minimising the Pollution Risk of Nitrates and Phosphates

Reducing pollution by Nitrates and Phosphates can be achieved through simple good management practices. Because Nitrates are very water soluble, farmers are encouraged to use practices that minimise the risk of nitrate pollution by, for example, carefully controlling the timing of the use of fertilisers to avoid over application, and considering all possible sources of nitrogen available to the crop in the calculation of application rates.

Phosphorus, on the other hand, attaches itself to soil particles, therefore the focus for the control of pollution by Phosphates is on minimising sediment loss from soil. Further reductions can be achieved by maintaining septic tanks and by installing phosphorus stopping processes at sewage treatment plants.

Good farm management practices are key to reducing the amount of agricultural Nitrates and Phosphates released into the environment, and schemes such as the Catchment Sensitive Farming (CSF) project and the creation and designation of Nutrient Vulnerable Zones (NVZs) are aimed at encouraging best practice in environmentally sensitive areas. NVZs are areas designated as being at risk of nitrate pollution from agriculture and include an estimated 58% of land in England. These areas are reviewed every four years to account for changes in pollution levels.


Other Grants Available:

Water Grant for Welsh Farmers

Sustainable Farming Grants

Flood Prevention Grants

Rural Development Grants

Farm Development Grants

Severn Trent Environmental Protection Scheme (STEPS)


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