| Summary: | Most of the EU member states along the Northeast Atlantic coastline have developed different fish-based indices to assess the ecological status of transitional waters due to the Water Framework Directive. To be valid, each method should show a good correlation with a gradient of human pressures. In order to define a comparable view of what should be 'good ecological status', we performed an intercalibration of seven fish-based indices according to a common pressure index. Anthropogenic pressures were assessed by expert knowledge and best available pressure data. Nearly 170 estuaries from Portugal to Germany and Northern Ireland, where fish data existed, were qualified with 15 candidate pressure indicators. Only the indicators that showed a good regression to the biological assessment were selected. A set of 8 indicators assessing habitat degradation, contamination and dissolved oxygen composed the final common pressure index. The biological response is expressed as an Ecological Quality Ratio (EQR: score ranging between 0 and 1) divided into five quality classes. However, the seven methods differ regarding the boundary setting between these classes. Linear regressions were used to show the correlation between the common pressure index and the EQR obtained for each estuary. All the seven fish-based indices displayed a significant pressure-response relationship. A harmonisation band for the class boundaries was defined using the bias to the median value for all methods obtained on the common pressure index scale. A multi-rater Kappa analysis controlled the agreements between all methods in the attribution of a quality class. All methods showed significant trend in EQR values decrease with an increasing pressure value. All methods were able to discriminate between good or better and moderate or worst status. This intercalibration process enabled the comparison of EQR values despite very different ecological assessment strategies, monitoring regime and type of estuary.
|
|---|