Assessing the pressures originating from agriculture on water allows to evaluate the relationship between the environment status and past and current agricultural policies. In addition it constitutes a preliminary step to perform risk and scenarios analysis, both essential for effective water resource management planning. The assessment of water pollution caused by nitrates from agriculture is important for monitoring the designation of Nitrogen Vulnerable Zones and to adopt or revise appropriate Action Programs under the Nitrate Directive (676/1991/EEC). The WFD requires Member States to develop plan of measures based on the assessment of pressure and impact, to be integrated in the river management plans, whose implementation is foreseen for 2009. Similarly, the Groundwater Directive (2006/118/EC) imposes Member States to perform an analysis of groundwater chemical status to be reported in the river basin management plans according with the Water Framework Directive. Therefore the assessment of nutrient pressures could contribute to implement the European legislation.
The need for assessment of agricultural pressures on environment was stressed by Commission communication COM(2000)20, which defined objectives for developing indicators of integration of environmental concerns into the CAP, called IRENA indicators. Concerning nutrients, gross nitrogen balance was designated as the indicator of agricultural pressures on water quality, as it allows identifying areas where nitrogen surplus or deficit may be cause of concern for natural resources and indirectly for human health. Moreover, nitrogen balance at farm level has been suggested as a tool to monitor the effects of agri-environmental policy (Brouwer, 1998).
The final report on IRENA indicators (EEA, 2005) emphasised that the calculation of national gross nitrogen balance can mask important regional differences, while regional gross nitrogen balances (i.e. gross nitrogen balance computed at finer spatial resolution) would provide a better indication of nutrient losses to water bodies. However, the estimation of regional gross nitrogen balance is accompanies by certain difficulties due to the lack of important data at regional level (such as manure, fertiliser application, crop yield coefficients) and the uncertainty in agronomic coefficients (EEA, 2005; Campling, 2005). Furthermore, these data, when available, refer to national or administrative territorial unit, which are less suitable for environmental studies, the appropriate study unit being a river basin.
Several studies have contributed to develop methodologies to estimated regional nitrogen balance, using the CORINE land cover to spatialise the statistical data at catchment scale, such as Crouzet (in EEA, 2001) for the basins of the Elbe and the Loire and Campling et al. (2005) for EU-15. So far, the phosphorus balance has not been studied with the same interest.
Rae data available for administrative regions (economic data) are inappropriate for analysis for geographical and spatial reasons. The task is to redistribute the statistical data collected and aggregated in administrative units, into the relevant zones, that are catchment units (EEA, 2001), as they constitute the natural frame for studying and managing water resources efficiently. The spatialisation of administrative data constitutes therefore the first step for the integration between the economic and the environmental systems.
The assessment of spatial nutrient pressures together with information on farm management practices, soil and climatic conditions, would allow to estimate risk of nutrient losses in water bodies, providing support to European environmental policy.