Farmers have been taking action to improve water quality for years. Despite much hard work and investment, some New Zealand rivers still aren’t meeting community expectations for purity, swimmability and mahinga kai (food and resources).
It’s a discouraging and thankless situation for land managers, who know how much effort they and their neighbours have made, and yet have no way to measure the overall impact of their work on New Zealand’s water quality.
Meanwhile, the dairy sector has expanded significantly, with a 40% increase in dairy-farmed land making it even more difficult to connect improvements in land management with changes in water quality.
Our Land and Water, one of 11 National Science Challenges that fund research aimed at solving New Zealand’s biggest problems, recently investigated the impact on water quality of adopting better practices on dairy, sheep and beef farms.
The researchers wanted to understand how effective on-farm mitigations have been so far, by comparing losses of nitrogen (N), phosphorus (P) and sediment in 1995 and 2015, and what would be possible for future water quality in 2035 if every farm in New Zealand adopted every known mitigation.
This information is crucial to helping farmers in degraded catchments decide whether to continue investing in mitigation actions or consider making changes to land use or land-use intensity.
“When we look at adopting all the established mitigations that we have now, most New Zealand catchments can get most of the way towards meeting the current water quality objectives,” says Professor Richard McDowell, chief scientist at Our Land and Water.
“We've got plenty of work we can do with the stuff we know now, so let’s get on and give it a go.”
We've summarised the findings of this analysis into a short Research Findings Brief:
Despite the efforts of many farmers to care for our water, at the same time on other farms land use changed and farming intensified.
Land area used by dairy expanded 40% between 1995 and 2015, and together with changes on farm such as increased fertiliser use, total dairy production increased by around 160%. The land area occupied by sheep and beef contracted, but the intensity of production per hectare increased.
This increased food production continued to put pressure on freshwater by increasing total nitrogen loss. Mitigations were not sufficient to offset these increased nitrogen loads.
Our Land and Water pulled together a team to do a national-scale assessment of the effectiveness of mitigation actions. The Sources and Flows research programme estimated nitrogen (N), phosphorus (P) and sediment losses in 2015, and compared these to scenarios including:
The researchers combined data on geographic and mitigation efficacy to model the total losses of N, P and sediment for around 130 farm typologies, which considered landscape attributes (such as soil, topography and climate factors) and land use pressures (such as farm inputs and feed and stock management practices) that influence contaminant transport to water.
On average over Aotearoa between 1995 and 2015:
Note: Despite lower per hectare emissions, sheep and beef accounts for about three-quarters of national N, P and sediment losses, because much more land is in sheep and beef (8.3 million hectares) than dairy (2.3 million hectares).
“Most New Zealand catchments can get most of the way towards meeting the current water quality objectives” – Professor Richard McDowell
Putting mitigations into action takes time, knowledge and money. Not all farmers were able to adopt all known mitigations between 1995 and 2015 – but what if this is achieved in future?
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.
What is the absolute best-case scenario for water quality in 2035, through improvement in farm practice alone? Researchers estimated that if all known and developing mitigation actions could be implemented by all dairy and sheep and beef farmers, the potential load of contaminant entering rivers would decrease by 34% (nitrogen), 36% (phosphorus) and 66% (sediment).
For many catchments, this will be enough to meet current water quality objectives.
For other catchments, applying all known and emerging mitigations may be less pragmatic than some change in land use or land use intensity. Additional research from Our Land and Water has enabled the identification of where this is likely to be the case; see the interactive map, Total nitrogen excess and reduction potential.