Farming for Water Quality: Balancing Food Security and Nitrate Pollution in UK River Basins

Widespread pollution of groundwater by nutrients is an externality of modern intensive agriculture. Rising nitrate concentrations in freshwater have been of concern throughout the developed world for several decades. Initial worries focused on human health but more recently nitrate's role in eutrophication has also become a cause for concern. Because the impact on water quality often comes decades after land use change, the challenge for science is to produce an integrated model of catchment hydrology and quality applicable to the long time-scales involved and that can cope with the complexity of connectivity among land, aquifer, and river. This article discusses the balance between food production, and therefore food security, and protection of water resources. We use recent results from a catchment-scale model of the River Thames in the United Kingdom to demonstrate that the response time of catchments can be on the order of decades, given the delays induced by groundwater flow through aquifers. Historically, the main drivers for changes in N fluxes were massive land use change associated with wartime plowing of permanent pastures and postwar modernization and intensification of agriculture, leading to the current quasi-steady state of N-dependent but leaky agriculture. It is clear that restoration of water quality to mid-twentieth-century levels would require very severe changes in land use and land management, significantly affecting UK food supply and security. Moreover, the potential timescales for recovery are well beyond those of normal political cycles. Failure to act will mean a continued high level of nitrogen transfer to rivers, estuaries, and oceans, with potentially serious ecological implications, and continued emissions greenhouse gases to the atmosphere. Notwithstanding improved efficiency of agronomic methods, the situation is unlikely to change significantly without radical shifts in legislation or farm economics.