Principal component analysis: Development of a multivariate index for assessing eutrophication according to the European water framework directive

The discriminating power of eutrophication assessment schemes is often affected by the intercorrelation between cause (nutrient concentrations) and response (phytoplankton biomass and diversity) variables. Principal component analysis, a multivariate data reduction technique producing new sets of uncorrelated variables, was applied on nitrate, nitrite, ammonia, phosphate and chlorophyll α concentrations from coastal waters in the Aegean Sea, Eastern Mediterranean, and the first principal component was derived and evaluated as a eutrophication index on an independent dataset. The index, a linear combination of the five variables with almost equal weights, was found efficient in discriminating levels of eutrophication and critical thresholds characterizing oligotrophy, mesotrophy and eutrophication were set. The applicability of these thresholds for the implementation of the European Water Framework Directive was also examined thereof a five-level water quality classification scheme was developed.