Water quality varies widely between regions around New Zealand, even where there are similar land uses and pressures. This is because the natural landscape has a much bigger influence on water quality than land use alone.
A new approach to water quality modelling better accounts for the influence of the natural landscape. Researchers in the Physiographic Environments of New Zealand (PENZ) project, part of the Our Land and Water National Science Challenge, have developed a new methodology to integrate water quality data with existing map layers (such as soil, geology, and land cover) to map and model the processes that control the variability of water quality. When combined with a map of land use intensity, they can be used to model water quality.
PENZ researchers then combined these maps to create a Physiographic Environment Classification, which groups areas that have similar landscape features. Areas classified as the same Physiographic Environment will respond to land use pressure in a similar and predictable manner.
Physiographic science works ‘backwards’, using water composition to trace the water’s journey back through the landscape to understand how the landscape affects water quality.
The proposed Physiographic Environment Classification gives a high degree of confidence to water composition estimates. Importantly, it also enables farm and catchment efforts to improve water quality to be matched to the landscape, with higher certainty regarding effectiveness.
Examples of ‘on the ground’ management practices that can be informed by physiographic science include land use management practices (eg selection of stock wintering paddocks), implementation of physical mitigation measures (eg riparian planting, peak runoff control), and optimisation of fertiliser timing.
Regional councils (Northland, Auckland, Waikato, Bay of Plenty, Horizons, Canterbury, Southland) are sharing data and collaborating to enable the physiographic approach to be applied to their regions.
“Most importantly, this information needs to be accessible to land users to make a difference,” says PENZ researcher Dr Lisa Pearson of Land and Water Science. “To do this, we have an MPI Sustainable Farming Fund project that is developing an education portal that farmers will be able to use to see how and where contaminants like nitrogen leave their land, so that they can make well-informed land use decisions to reduce losses.”
A steering group of six Southland farmers representing different enterprises are guiding the content and design of the website and interactive app, plus industry representatives are working with the farmers to help tailor the website for their specific farming activities. A prototype will be ready by the end of 2019, with a national roll-out in 2020.
“We want to empower land users to make more effective decisions in land management and mitigations,” says Dr Pearson, “creating a future landscape and community that is more resilient, healthy and prosperous than it is today.”
For more information, see:
- Physiographic Environments of New Zealand
- For regional councils: Information on the physiographic approach (PDF)
- ‘A hydrochemically guided landscape classification system for modelling spatial variation in multiple water quality indices: Process-attribute mapping' in Science of the Total Environment, July 2019
You may also be interested in this paper, produced as part of the Sources and Flows programme: ‘A strategy for optimizing catchment management actions to stressor–response relationships in freshwaters' in Ecosphere, October 2018