The Ministry for Primary Industries (MPI) used physiographic science developed by Our Land and Water to inform new National Environmental Standards (NES) around intensive winter grazing. The new standards come into force on 1 May 2021, requiring winter grazing to meet specified permitted activity conditions, or obtain a consent.
Poor management of winter grazing on forage crops can result in animals trampling a paddock to deep mud (pugging) and stripping the land of vegetative cover. Bare land and pugging can result in water pollution due to increased runoff, erosion, and leaching of contaminants to waterbodies.
To support good wintering practices, MPI commissioned OLW researchers at Invercargill environmental consultancy Land & Water Science to write a report using physiographic science to assess the effect on water quality of the options for winter grazing standards proposed in the Action for Healthy Waterways discussion document.
The report used data produced by the Physiographic Environments of New Zealand programme (PENZ), led by Lisa Pearson and Clint Rissmann of Land & Water Science. PENZ developed a method that brings together data for climate, topography, geology, soils, and hydrological controls with analytical chemistry at a national scale, to map and model the landscape processes that (along with land use) control variation in water quality between regions and catchments.
In a fast-changing regulatory environment, physiographic science provides farmers with certainty, because a farms’ underlying soil and geology doesn’t change significantly over our lifetime
This approach clarifies the important role of landscape factors such as slope, soil structure and hydrology, and enables the identification of where risk is likely to be highest and where intensive winter grazing is likely to have minimal impact over water quality.
In a fast-changing regulatory environment, physiographic science provides farmers with certainty, because a farms’ underlying soil and geology doesn’t change significantly over our lifetime. For its report to MPI and the Ministry for the Environment, Land & Water Science used the predictive model and conceptual spatial map developed by PENZ to:
- evaluate the sensitivity of a range of landscape attributes (including overland flow, artificially drained soils, aquifer denitrification potential, slope, and soil pugging) to water quality contamination by intensive winter grazing,
- evaluate the sensitivity of proposed winter grazing slope thresholds, soil pugging risk and soil hydrological factors, using physiographic science to create a winter grazing risk framework for water quality (surface and ground water), and
- develop a national winter grazing risk map based on physiographic data, that ranks the landscape in terms of very low to very high risk to water quality from winter grazing.
A preliminary report with key recommendations was submitted to MPI in March 2020. One key recommendation was an upper slope threshold of 10° for intensive winter grazing. This information was used to support officials’ recommendation to set an upper slope threshold of 10°, included as a condition of the permitted activity standards in the new National Environmental Standards for Freshwater.
While the NES uses a whole-property calculation for the assessment of slope, a finer 0.25ha resolution is possible when using a physiographic map. Identifying slope on this 0.25ha scale will be possible for farmers later this year when a prototype physiographic map website will be complete, powered by multiple layers of land classifications that can be used to identify risk to water quality.
While the NES uses a whole-property calculation for the assessment of slope, a finer 0.25ha resolution is possible when using a physiographic map.
Physiographic maps are a useful tool to create clarity on how land use and land attributes contribute to water quality. The maps simply communicate a complex synthesis of data sources, showing how multiple natural processes combine with land use to influence water quality risk.
The new physiographic map website will help inform farm management decisions and the placement of mitigations and interventions. For example, by knowing where water will drain through a winter forage crop paddock, grazing strategy can be managed accordingly, leaving high-risk water convergence areas until last or avoided altogether.