Application of specific exergy to macrophytes as an integrated index of environmental quality for coastal lagoons

This work aims to explore the application of specific exergy on macrophytes as an integrated index to assess ecosystem health in coastal lagoons, and to analyse its possible application in view of the implementation of the Water Framework Directive of the European Union (European Commission, 2000). Exergy and specific exergy are calculated as a function of the biomass multiplied by a weighting factor (β), which express the quantity of information embedded in the biomass. Until now only few general values of β have been published. Therefore, we have extended the calculation of β-values for 244 seaweed and seagrass species which are common in Mediterranean coastal lagoons. The estimated β-values have been then compared with macrophyte-based indicators which have been recently developed, namely the Ecological Evaluation Index and the IFREMER classification scheme. Overall, we found a good agreement between β-values and macrophyte indicators. Furthermore, the specific exergy was calculated for 71 sites in coastal lagoons of Southern France and compared with existing classification schemes, finding a good agreement between them. As a result, we argue that specific exergy may be used as an integrated index that is able to synthesize and complement existing approaches.