The potential impacts of future climate and land-use changes on groundwater nitrates in England & Wales

Nitrate water pollution, which is mainly caused by excess nitrogen fertiliser application on agricultural lands, remains an international problem. To tackle this issue, several methods, e.g. the nitrate-time-bomb (NTB) modelling, have been undertaken to analyse the trend of groundwater nitrate concentration to support the UK government’s policymaking in handling nitrate water pollution. However, it is also important to consider the influencing factors such as land-use change and climate change when estimating future trends in nitrate leaching to groundwater of Great Britain (GB). Therefore, it is timely and necessary to develop new methods to answer the crucial question: how would future land-use change and climate change affect the groundwater nitrates of GB? A national-scale model, called LUC-NIF, has been developed in this study to implement the complicated principles of the European four land-use-change scenarios in GB. After the model calibration, validation and sensitivity analysis, the spatio-temporal land-use maps and nitrate leaching maps under the four scenarios have been generated for GB (2018–2080). The UK Climate Projections (UKCP) which provides projections of climate change in the UK were processed and adapted to produce eleven scenarios of Future Flow Climate data (11 RCM runs). The rainfall and potential evapotranspiration (1km by 1km) from 11 RCM runs were fed into a national groundwater recharge model to generate groundwater recharge data under climate change. The NTB model, which simulates the nitrate transport in the unsaturated zones and aquifers, was integrated into the LUC-NIF and the hydrological model to simulate the groundwater nitrate concentrations in 28 major aquifers in England & Wales under the projected 4 land-use change and 11 climate-change scenarios. The results show that the total leached nitrate from the soils will have declining trends from 2018 under all the scenarios but with variant decreasing rates, and will reach the historical levels of 1942–1954 by 2080. The average groundwater nitrate concentrations in 28 aquifer zones reach their own peak values at different years before starting to decrease. The results produced in this research can help people get a glimpse into the likely nitrate-leaching and groundwater nitrate trends in GB, however, the limitations of this research should be considered when using these results