ng, sediment disposal and land reclamation.
The study focused on the trends of water and sediment contamination by metal pollutants (arsenic, cadmium, copper, chromium, mercury, nickel, lead and zinc) and the response of these areas to water treatment programmes in recent years.
The chemical status of these water bodies was assessed using two approaches: (i) following the principle of one out, all out as established by the WFD --any metal in waters over the EQS will result in the whole body of water failing to achieve the chemical status--, and (ii) combining an analysis of the chemical quality of both the surface waters and the underlying sediment, using a weighted methodology proposed by these researchers previously.
Using the first approach, few of the water bodies achieved good chemical status, and the percentage of systems meeting this status falls over time, having reached values close to zero in recent years. Using the second approach, more than 50 per cent of the water bodies achieved Good Status, with the percentage of systems meeting this status remaining steady over time.
The researchers argue that the second approach is more accurate in assessing chemical status as it is better at discriminating between less polluted water and that which is highly polluted, and more in line with the responses of the biological indicators. Moreover, when all the information was incorporated --at the level of water bodies-- from various biological, hydromorphologic, physico-chemical and chemical indicators, the ecological quality of water bodies in the Basque Country showed progressive recovery, especially since 2000, when most of the water treatment plans were completed.
By considering both water and sediment analysis in determining the status of water quality, resources could better be targeted at those water bodies where levels of pollution have a greater negative effect on the biological elements. However, the researchers say further research is needed on EQS measurements in water and the interpretation of chemical concentrations of contaminants in sediments.
*Source: Tueros, I., Borja, A., Larreta, J., Rodriguez, J. G., Valencia, V., Millán, E., (2009). Integrating long-term water and sediment pollution data, in assessing chemical status within the European Water Framework Directive. Marine Pollution Bulletin. 58:1389-1400