Pollution regimes and variability in river water quality across the Humber catchment: interrogation and mapping of an extensive and highly heterogeneous spatial dataset

Water quality inter-relationships based on an extensive Environment Agency database are used to identify seven key types of clean and polluted riverine environments within the Humber catchment. These types were selected on the basis of linear separations between average concentrations of ammonium, chloride, dissolved nickel and chromium and acid-available particulate nickel and chromium. However, a more detailed analysis of determinand and flow relationships at each type locality revealed complex patterns due to the highly variable nature of pollutant sources at the local scale. The information presented contrasts systems at a larger scale, where simpler integrated features are observed, and which can be represented by two-component mixing models. Scale and hydrology seem to be important features in determining the simplicity or complexity of determinand inter-relationships, and the implications of these findings are discussed.