European Environment Agency (EEA)

Assessing water quality in Europe using stratification techniques


Courtesy of European Environment Agency (EEA)

This report aims to provide information in relation to the trends of major nutrients in rivers. It focuses both on the trends considered as indicators of water quality status and on the possible differences in trends in relation to main driving forces (agriculture, urbanisation). Referring to the driving forces — pressures — state — impact — response (DPSIR)
assessment framework of the EEA, the relationships drivers — state have been systematically analysed at different geographical levels.

The purpose of these analyses is to consider if measurable improvements of river-water status and their significance can be assessed, and if these trends can be reasonably related to relevant driving forces, especially the ones with the largest impact, and the policies put in place to mitigate the environmental impacts of these driving forces. A complementary
goal of the methodological improvement is to reduce the time lag between a policy implementation and the observation of its effects. Such assessments must be applicable to all the areas covered by the EEA mandate. This poses two different challenges. First of all, the statistical methodology must be tested on a diversified area to demonstrate its capacity to respond to the questions mentioned above. This is the subject of this report which took stock of the provision of all nationally monitored data and reference systems in France kindly provided by the French Ministry of Ecology and Sustainable Development.

Secondly, the use of comparable reference systems, homogeneous at the European level, should be checked. This is the purpose of further applications that are underway, partly based on the European spatial assessment catchment system (CCM) being developed by the European Commission Directorate General Joint Research Centre (DG JRC).
The methodology used in this study improves on previous approaches used in assessments carried out by the EEA by:

  • replacing assessments based upon station categories by stratified assessment of catchments. The relative weight of catchments replaces the proportion of stations, thus providing statistically comparable aggregated concentration values for the different determinants;
  • defining accurately and in a reproducible way the different strata that allow comparable and meaningful relationships to be established between trends in driving forces and trends in quality status;
  • providing estimates of the date on which targets can be achieved expressed as range of years with likelihood of the assessment.

This is a key issue to policy effectiveness assessment. The methodological improvements reported in this document are in line with the EEA objective of contributing to the European development towards the production of 'water accounts'. This approach follows the SEEA (System of Economic and Environmental Accounts) methodology to better link physical and economical components of the environment. SEEA derived approaches have now been raised as 'statistical standards' at the UNSD and Estat levels, hence contributing to making the environmental accounts comparable at the World level.

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