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An introduction to the nitrate problem

Nitrogen is essential for the growth of plants and small amounts of nitrate are naturally present in groundwater. Elevated levels of nitrate largely stem from the nitrogen contained in fertilisers and manure that are used to increase arable crop growth. When rain or irrigation water washes away the excess fertiliser, it percolates through the soil where aerobic bacteria transform the nitrogen into nitrate. The nitrate enriched percolate then discharges into the surface or ground water. This is problematic because elevated nitrate concentrations are a risk to human and animal health, and aquatic ecosystems. It also increases the cost of supplying clean drinking water to consumers.

Despite the well known connection with agricultural activities, it remains difficult to determine reliably the contributions from different possible sources to locally observed high nitrate levels. But for effective remediation, it is obviously important to distinguish the origin of nitrate pollution. The use of mineral fertilisers, application of manure produced by different animals, leakage from the sewage system, atmospheric deposition and geologically retarded release of nitrate discharged earlier, may all contribute to local problems. Stable isotope measurements can help to determine the origin of nitrate pollution.

Further reading:

Inventory of the various nitrate sources in Europe, a study by the European Environment Agency:
Source apportionment of nitrogen and phosphorus inputs into the aquatic environment (icon)

Implementation of Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources (icon) at the Environment DG site





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