Impact of climate change on future groundwater nitrate

Nitrate concentrations in groundwater are already a serious problem with many groundwater abstractions containing nitrate concentrations which exceed the drinking water limit, Under current climate conditions and agricultural practices, concentrations are predicted to continue to rise. The potential impacts of climate change on such groundwater concentrations in groundwater can be assessed using a source-pathway receptor framework. Climate changes such as temperature, precipitation amounts and distribution, and the underlying increases in atmospheric carbon dioxide concentrations will impact on both soil processes and agricultural productivity. This has been well-studies in terms of crop yields and potential changes in cultivars, crop type and the northwards extension of cropping area. However the impacts of these changes on the N source term remains difficult to predict. Studies of soil processes suggest climate change is likely to lead to increased nitrate leaching from the soil. Other source terms include non-agricultural sources, such as urban areas and atmospheric deposition. The implications for nitrate leaching to groundwater are not yet fully understood but predictions suggest that leaching may increase under future climate scenarios. Climate change will also affect the hydrological cycle with changes to recharge, groundwater levels and resources and flow processes. 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. This will impact on concentrations of nitrate in abstracted water and other receptors on an annual timescale. The longer term impact on aquifer pathways needs to be evaluated. 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 if key changes to agricultural practice are not made. However inherent difficulties of estimating key parameters mean that these predictions are within the margins of uncertainty. These changes may be masked by nitrate reductions from improved agricultural practices. Future impact may also be driven by economic responses to climate change. A range of adaption measures need to be identified and these need to be derived through interdisciplinary including collaboration between regulators, the farming community, government departments and scientists