Hydrochemical interpretation of groundwater-surface water interactions at catchment and local scales, Lake Rotorua catchment, New Zealand

• Published in: Journal of hydrology, New Zealand New Zealand, 2015, Vol.54 (1), p.11-32
• Main Authors: Donath, Franziska M., Daughney, Christopher J., Morgenstern, Uwe, Cameron, Stewart G., Toews, Michael W.
• Format: Article
• Language: English
• Subjects: Analysis; Catchments; Environmental aspects; Groundwater; Hierarchical clustering (Cluster analysis); Hydrology; Lakes; Principal component analysis; Principal components analysis; Sampling; Statistical methods; Water chemistry; Water quality; Winter
• ISSN: 0022-1708; 2463-3933

Due to land-use intensification, deteriorating water quality has threatened the cultural and environmental values of Lake Rotorua, which is located in a circular caldera basin, central North Island, New Zealand. The objective of this study was to employ hydrochemical and multivariate statistical methods to elucidate groundwater-surface water interaction in the lake catchment and, in particular, in the Ngongotaha Stream subcatchment. Sampling took place under baseflow conditions in winter/spring 2003 and winter 2012 in the catchment and subcatchment-scale studies, respectively. Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were independently applied to different sets of parameters comprising major and minor ions and hydrochemical field parameters. PCA showed that hydrochemical variation at both scales was largely related to the concentration of total dissolved solids and hence to natural water-rock interaction and, to a lesser degree, to redox potential. HCA at both scales suggested that hydrochemistry was driven by interaction between water and the major lithologies in the study area, with human and geothermal influence being important in some areas. This study has shown that PCA and HCA are complementary techniques that can be usefully applied across catchment and subcatchment scales to increase our understanding of groundwater-surface water interactions in order to improve land and water management around Lake Rotorua.