New Zealand's National River Water Quality Network 2. Relationships between physico‐chemical data and environmental factors

The first 2 years’ physico‐chemical data from the National River Water Quality Network's 77 river and stream sites were related to environmental variables such as catchment erosion, soil and rock types, and land use. Multivariate analysis reduced the physico‐chemical data to seven groups of determinands: major ions (as indexed by conductivity), P species (DRP and TP), N species (TN and NO 3 ‐N), “organics” (BOD 5 and NH 4 ‐N), clarity, absorption coefficient (g 440 ), and a combination of DO and pH. The river sites were grouped into nine clusters using these seven determinand groups; 65 sites (containing the most pristine waters, a majority of which are located in the South Island) were contained in just four clusters. Differences between the clusters are best explained by the concentrations of P species and “organics”. Discriminant analysis was used to relate the physico‐chemical site clustering to environmental variables; it indicated that the degree of pasture development and its associated variables (e.g., negligible to moderate erosion, high mean annual water temperature, high percentage recent soils, low mean catchment elevation) are the most important factors affecting water quality.