New Zealand Process Attribute Mapping: Hydrochemical surface and groundwater data (2007-2017)

This dataset was developed to evaluate the method for Rissmann et al. (submitted to JGR Biogeosciences) 'A hydrochemically guided landscape-based classification for water quality: a case study application of process-attribute mapping (PoAM) at a national scale'. The surface water dataset was produced from the collation of chemical analyses of low, median, and event flows taken from 730 long-term surface water monitoring sites across the regions of Northland, Auckland, Waikato, Bay of Plenty, Manawatū-Whanganui, Canterbury, and Southland (representing 58 % of New Zealand), between 2017 and 2019. Across the same regions and for the same time period, data for the sample chemical constituents were collected at 2,191 long-term groundwater monitoring sites. The respective hydrochemical datasets for surface water and groundwater were subsequently combined with pre-existing hydrochemical data collected between 2007-2017 and median values calculated. The hydrochemical analytes include major constituents (Ca, Cl, dissolved organic and inorganic carbon, total alkalinity and HCO3 alkalinity, K, Mg, Na, SO4, SiO2), minor constituents (B, Br, F, Fe, I, Mn), water quality (total nitrogen, nitrate, nitrite, ammoniacal nitrogen, total phosphorus, dissolved reactive phosphorus, turbidity, clarity, E.coli and faecal coliforms), and field parameters (dissolved oxygen, electrical conductivity, oxidation-reduction potential, pH (field, lab), temperature). Not all surface water and groundwater sites have all analytes measured. Internal quality control in this project removed sites with point source impacts, including sites downstream of municipal wastewater discharges. Site water quality medians for each monitoring location were combined with the mean process attribute gradient score for the capture zone. Process attribute gradients represent the four dominant processes controlling water composition, specifically atmospheric, hydrological, microbially mediated redox, physical and chemical weathering. Further details can be found in Rissmann et al. (submitted).