Results of the principal component analysis (PCA) of the environmental parameters of 30 stations. (a) Correlation circle showing correlations among the 11 environmental parameters (Cond. electrical conductivity; Transp. transparency). (b) Distribution of the barycentres of each location (coloured circles); solid lines link the station to each location and each season to the corresponding location. (c) Distribution of the barycentres of each season; solid lines link the station at each location to the corresponding season.