Principal components analysis (PCA) of physico-chemical variables. Sites are shown according to region and site numbers coded as B (July 2014) or C (January/February 2015). Physico-chemical data were not collected during the first survey (November 2013). The first two principal component axes are displayed, with PC1 and PC2 explaining 34.7 and 28.2% of the variation in the physico-chemical data, respectively. Table 2 provides the units in which each of the variables was measured.