The impact of climate change on nitrate concentration in groundwater

The potential impacts of climate change on nitrate concentrations in groundwater of the UK are complex since nitrate leaching and migration through the aquifer could be affected. We reviewed these potential impacts for the UK using a source–pathway–receptor framework.

Changes to nitrate inputs

Simplified nitrogen cycle highlighting soil processes.

The main inputs of nitrate to UK groundwater are from agricultural sources. Changes in temperature, precipitation quantity and distribution, and atmospheric carbon dioxide concentrations will affect the agricultural nitrate source term (inputs) through changes in both soil processes and agricultural productivity.

This has been well studied in terms of crop yields and potential changes in cultivars, crop type and the northwards extension of cropping area but the impacts of these changes remains difficult to predict. Studies of soil processes suggest climate change is likely to lead to increased nitrate leaching from the soil under future climate scenarios.

Non-agricultural source terms, such as urban areas and atmospheric deposition, are also expected to be affected.

Changes to pathways by which nitrate enters groundwater

The implications for the rate of nitrate leaching to groundwater as a result of these changes are not yet fully understood but predictions suggest that leaching rate may increase under future climate scenarios. Climate change will affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. Pathways by which nitrate enters groundwater will therefore be modified.

The predicted impacts are variable but many predictions suggest an overall decrease in recharge and a fall in water levels and almost all predict an enhanced seasonal variation in water levels.

Impacts for receptors

These changes will impact on concentrations of nitrate in abstracted water and other receptors, such as surface water and groundwater-fed wetlands. The implications for nitrate leaching to groundwater as a result of climate changes are not yet well enough understood to be able to make useful predictions without more site-specific data. The few studies which address the whole cycle show likely changes in nitrate leaching ranging from limited increases to a possible doubling of aquifer concentrations by 2100.

Mitigation or adaptation?

Any climate change induced increases in nitrate inputs to groundwater may be masked by nitrate reductions from improved agricultural practises, but a range of adaptation measures needs to be identified. Future impact may also be driven by economic responses to climate change.