Phytoplankton Reservoir Trophic Index (Prti): A New Tool For Ecological Quality Studies

The Phytoplankton Reservoir Trophic Index (PRTI), based on the relative abundance of phytoplankton in reservoirs, was applied to 62 reservoirs, all in the territorial division of the Ebro River Basin, Spain. We compared the results of the PRTI to the Carlson Trophic State Index (TSI), based on the concentration of chlorophyll a in an integrated water sample through the photic depth. The PRTI allows assessment of the trophic status of different reservoirs based on phytoplankton densities from an aliquot of a vertically integrated sample. The occurrence of each phytoplankton species in relation to eutrophication was derived from a canonical correspondence analysis between the phytoplankton species and 8 physicochemical variables. The PRTI is used in this study to classify reservoirs into 5 ecological status categories according to the European Water Framework Directive. This methodology has been applied annually from 2006 to 2017 for ecological quality assessments of reservoirs in Spain. The PRTI seems to be a valid index to determine the trophic status of reservoirs and extends information beyond that reported in the TSI.