Roger Young | January 20, 2021 from GlobalHQ on Vimeo.
The aim was to further understand how effective better on-farm mitigations have been so far, by comparing losses of nitrogen (N), phosphorus (P) between 1995 and 2015, and what could be possible for water quality in 2035 if every farm in New Zealand adopted every known mitigation.
That information could be used to help farmers in degraded catchments to decide whether to continue investing in mitigation actions or consider making changes to land use or land-use intensity.
The research showed that at least 43% of NZ’s agricultural land (31% of NZ’s total land area) is in catchments that are under pressure.
The current load is twice the maximum allowable load in parts of Waikato, Manawatu-Whanganui, Marlborough, Canterbury, Otago and Southland.
If all on-farm mitigation actions were implemented by every dairy, sheep and beef farmer by 2035, it is possible for the potential N entering rivers to decrease by 34% compared to 2015.
For 96% of catchments, this will be enough to meet the national limits for dissolved inorganic N (1mg DIN/L) that were considered for inclusion in national policy earlier this year, but are not part of current policy.
Similarly, if all mitigations were implemented by every dairy, sheep and beef farmer by 2035, the potential P load entering rivers would drop by 36%, while sediment would be 66% lower.
For many catchments that would be enough to meet current water quality objectives.
The research showed that NZ rivers would be in much worse condition today if farmers had not adopted better practices between 1995 and 2015.
Significantly more N (45%) and P (98%) would have entered rivers from dairy-farmed land during this period if farmers had not adopted better practices.
The most effective N and P mitigation practices used over the period were stock exclusion, improved effluent management and improved irrigation practices.
On sheep and beef-farmed land, 30% more sediment would have entered rivers during the same period if farmers hadn’t changed their practices.
The most effective sediment mitigation practices used over the period were planting more trees, excluding stock from waterways, and soil conservation works.
To help get a better idea of where water quality is under the most pressure – and where that pressure can be relieved by 2035 – a new interactive map has been developed.
It shows which rivers, lakes and estuaries are under the most pressure from agriculture and whether all farmers in those areas adopting all known mitigation actions will ease the pressure.
The map allows users to zoom in to any of NZ’s catchments or regions, and swipe between two views. Swiping to the left reveals the total N load in excess of current regulatory objectives. Swiping to the right reveals the potential for on-farm actions to reduce N loss from land to water.
OLAW chief scientist Professor Richard McDowell says knowing how important our rivers and lakes are to all New Zealanders, land stewards need to know where community expectations for water quality can be met through improvements in farm practice – and where current land uses may be unsuitable.
“Aotearoa’s freshwater quality is degraded, and in some areas much more than others,” McDowell said.
“However, the current situation is much better than it would have been if no action was taken while the same increase in food production occurred.
He says many land managers have taken pragmatic and effective action to care for the land over the past 20 years.
“In many catchments, accelerating this work will be enough to meet current water quality objectives, particularly if land stewards plan to meet catchment objectives together,” he said.
“For other catchments, applying all known and emerging mitigations may be less pragmatic than some change in land use or land use intensity.
“This map helps New Zealanders see where meeting limits is achievable, and where limits aren’t likely to be met under existing land use.”
Register to record farmer efforts
To find out which actions work best, Our Land and Water is one year into a three-year project to create a free online tool to record efforts to improve water quality within rural catchments.
Cawthron freshwater sciences group manager Roger Young says one of the goals is to give landowners confidence to invest in the most efficient actions, accelerating investment in catchment improvements.
The register will also give people all over NZ greater awareness of efforts under way to improve fresh water and a clearer picture of what has been achieved so far.
The tool that is ultimately developed will improve the ability to link actions on land with changes in water quality at monitoring sites.
Information will be displayed in a way that will enable people in one catchment to make comparisons with other catchments to see what has worked elsewhere over what timeframe.
It will be presented on a catchment scale, protecting the confidentiality of individual farmers.
