The nitrate time bomb : a national view of nitrate storage and lag time in the unsaturated zone of the UK

Nitrate pollution in freshwater, which is mainly from agricultural activities, remains an international problem. It threatens environment, economics and human health in the UK. There is a rising trend in nitrate concentrations in many UK freshwaters (both groundwater and surface water). Research has shown it can take decades for leached nitrate from the soil to discharge into freshwaters due to the ‘store’ of nitrate and its potentially long time travel time in the unsaturated and saturated zones. Because of environmental and legislative pressures there is an urgent need to take this time lag into account. A process-based GIS model was developed to investigate nitrate transport in the unsaturated zones of UK aquifers, and to predict the arrival time for peak nitrate loading at the water table at the national scale. This model was also applied at the catchment scale in the Eden Catchment (UK), in conjunction with simple GIS based groundwater flow and transport models. This research can improve the scientific understanding of nitrate processes in groundwater systems, and support the effective management of future nitrate concentrations in the aquatic environment. The methods and tools developed in this study can be transferable to other areas.