Eutrophication Assessment in Basque Estuaries: Comparing a North American and a European Method

Eutrophication in marine ecosystems is an important problem that requires an accurate assessment. Although Basque estuaries (northern Spain) have historically been under high anthropogenic pressure, no specific eutrophication assessment method had been applied in these waters. In this study, a method employed in the Basque Country (BC) to assess the risk of failing to achieve good ecological status under the requirements of the Water Framework Directive (WFD) was adapted to exclusively assess the risk of eutrophication. This method is based on the driver-pressure-state-impact-response approach. The results from this method (called WFD-BC method) were compared to the results from Assessment of Estuarine Trophic Status (ASSETS; a specific method developed in the US to assess estuarine trophic status in a pressure-state-response approach). The nutrient pressure was better characterized with the WFD-BC method due to the local hydrographic conditions (i.e., small and river-influenced estuaries) that were not well accommodated by the ASSETS method. In contrast, the WFD-BC results for assessment of state generally reflected worse conditions than the results from the ASSETS method due to the different indicators employed and the way these are integrated in the WFD-BC method. Overall, the WFD-BC method showed a good potential to assess eutrophication. However, to improve it, a lower weight for the benthos and macroalgae is recommended for evaluating state.