Baseflow water chemisty in New Zealand rivers 2. Influence of environmental factors

Abstract

Baseflow water chemistry in 96 New Zealand rivers was related to selected environmental variables quantifying lithology, land use, topography, and hydrology. The river sites were clustered using five water quality variables: major ions, phosphorus species, organic and nitrogen species, calcium, and nitrate. Eleven site clusters were identified and the differing water quality regimes discussed. The effect of the environmental factors on water quality was investigated using discriminant analysis. The resultant model assigned 73% of the sites to the correct cluster. The most important environmental variables determining water quality were hydrological variables such as specific yield, and proportional areas in the catchment of soft sedimentary rock, intensive pasture (which was negatively correlated with steep slopes and high altitudes), exotic forest, and volcanically derived rock. Multiple regression equations relating individual water quality determin‐ands to these environmental variables were derived. All equations were highly significant (P < 0.0001) and R ² values ranged from 0.65 to 0.83 for conductivity and major ion species, and from 0.46 to 0.70 for nitrogen and phosphorus species. These equations could be used to give a rough indication of likely water quality at unsampled sites which would be valuable in a variety of water management situations.

Keywords:

• water quality
• baseflow
• environmental variables
• clustering
• discriminant analysis
• multiple regression