2.3. Statistical methods
Cluster analysis was performed using Statistica version 13 (TIBCO Software Inc.) on a selection of variables listing elemental, ionic and DOC concentrations , with the selection criterion that only variables with 33% or fewer values < LOQ (or below blank) were taken into account to avoid artifacts in grouping. Prior to cluster analysis, values <LOQ (or below blank) were replaced by half LOQ (or blank, whichever was higher). All data was standardised (z-transformed) within variables. Clustering was performed using Ward’s method and squared Euclidean distance. This analysis may be cross-compared with the principal component analysis presented in Suppl. Mat. 1 .
Enrichment factors (EFs) relative to average concentration of elements in the suspended sediment of World rivers (after Viers et al. , 2009 and Taylor, 1964) have also been calculated and are shown in Table S4 (Suppl. Mat. 1 ).