Nitrogen in water is a critical aspect of water needed for thriving aquatic ecosystems. While nitrogen is essential for plant growth and the environment, excessively high levels of nitrogen in water can have detrimental effects. In this blog, we’ll explore the consequences of elevated nitrogen levels in water and why it matters.
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What is Nitrogen?
Nitrogen (N) is a crucial chemical element. This element is vital for life, as it is a key building block of proteins, DNA, and other organic molecules. Nitrogen makes up 78% of Earth’s atmosphere – but this form of nitrogen isn’t useful for most living things. As a result, the nitrogen cycle must exist.
The nitrogen cycle (pictured below) is needed to create forms of nitrogen that plants can absorb, which is then passed up the food chain once animals eat the plants. The different nitrogen forms present within the environment during the nitrogen cycle are:
- Most of our planet’s atmosphere is made up of this gas.
Nitrogen gas generally can’t be used as a nitrogen source by most living things.
- Produced when nitrogen gas is converted by bacteria in soil (nitrogen fixation)
Ammonia can be used as a nitrogen source by some plants, but it is usually converted to other nitrogen forms.
- Formed when ammonia reacts with water in soil.
Ammonium serves as an important nitrogen source for plants.
- Bacteria in the soil convert ammonia or ammonium into nitrite (nitrification #1)
Nitrite is an intermediate nitrogen form in the nitrogen cycle.
Formed when nitrite is converted by soil bacteria (nitrification #2).
Nitrate is the main nitrogen source for plants.
Nitrate can be converted back into Nitrogen gas by bacteria (denitrification) to complete the nitrogen cycle.
Nitrogen in Water Across Ireland
Low nitrogen levels in water can promote aquatic plant growth. However, excess levels can be detrimental. Nitrogen can enter water sources through a variety of pathways, including industrial discharges, and sewage. However, the main cause of nitrogen pollution is agricultural practices.
Nitrate levels in water have increased over the last few years due to the runoff of inorganic fertilisers and animal manure into water sources. According to the EPA’s Water Quality in 2025: An Indicators Report, nutrient pollution remains one of the biggest challenges facing Ireland’s waters, with 43% of rivers showing nitrate concentrations that are too high, particularly in the east and southeast of the country.
In Ireland, the maximum allowable nitrate concentration in drinking water is 50mg/l NO₃, as set out under the European Union (Drinking Water) Regulations 2023 (S.I. No. 99/2023). Any result above this level is treated as an exceedance and must be investigated.
Environmental Effects of Excess Nitrogen in Water
Elevated nitrogen levels in water can lead to algal blooms, which are rapid, excessive growths of algae. These blooms can have serious consequences for aquatic ecosystems.
When the algae die and decompose, they deplete oxygen levels in the water, leading to “dead zones” where fish and other aquatic life cannot survive. Examples of damaging Algae Blooms can been seen in Northern Ireland’s Lough Neagh (below).
Nitrogen pollution can harm fish and wildlife in multiple ways. The reduced oxygen levels can suffocate fish, and some forms of nitrogen, like ammonia, can be directly toxic to aquatic life.
High nitrogen levels can also disrupt the food chain by promoting the growth of certain species over others.
Elevated nitrogen levels can lead to changes in water chemistry, including increased acidity. This can further impact the health of aquatic organisms and disrupt the balance of the ecosystem.
Health Effects of Excess Nitrogen in Water
Nitrates can interfere with the body’s ability to transport oxygen, leading to a condition known as methemoglobinemia (blue baby syndrome). Infants are particularly vulnerable as their bodies cannot efficiently convert nitrates into harmless substances. Other dangers associated with excess exposure to nitrogen in water include colorectal cancer, thyroid disease & neural tube defects.
Those most at risk of damaging nitrogen exposure are:
1) Users of Public Drinking Water Supplies: In cases where water treatment is insufficient or fails, consumers of public drinking water supplies may be at risk of nitrate exposure.
2) Private Well Owners in Farming Areas: In rural regions where agriculture is prevalent, private well owners may be at heightened risk due to nitrate contamination from agricultural runoff.
Southern Scientific’s Water Monitoring
At Southern Scientific, we test over 10,000 drinking water samples each year in our ISO 17025-accredited laboratory. Our client base includes more than 1,000 organisations, such as local authorities, Uisce Éireann (Irish Water), group water schemes, and Bord Bia customers.
Regular testing for nutrient contamination, including nitrogen levels, is crucial to preventing exposure risks. Our easy-to-use standard water test can specifically detect nitrates, helping ensure safe water quality!
