PCA (Principal component analysis) of the 11 environmental variables, excluding longitude, listed in Table 1 (transformed and normalised).

<p>Dots represent sites within estuaries. Vectors show the two-dimensional (PC1 and PC2) correlation structure among the environmental variables (% of variance explained = 52.4). Abbreviations: catch a = catchment area, disturb a = % of disturbed area of the catchment, est a = estuary area, flushing t = flushing time, lat = latitude, MGS = median sediment grain size, sorting = sediment sorting, OM = sediment organic matter, silt/clay = % sediment silt/clay content, TN flux = flux of total nitrogen, TN ratio = ratio of total nitrogen loading pre-European settlement to present.