NZ’s rivers would be in much worse condition if farmers hadn’t improved their practices over the past 20 years, according to research findings released recently by Our Land and Water National’s (OLAW) Science Challenge.
Without the mitigation efforts, scientists estimate between 1995 and 2015 there would have been 45% more nitrogen and 98% more phosphorus going into our waterways.
They say this has mainly been achieved through excluding stock from streams, improved effluent management and improved irrigation practices.
That’s the good news. The bad news is at least 43% of NZ’s agricultural land is in catchments that are under pressure from excess nitrogen, meaning more needs to be done to remedy this.
But researchers say that can be turned around within 15 years, and if all known and developing mitigation actions were implemented by all farmers, nitrogen entering rivers would decrease by 34%, phosphorus by 36% and sediment by 66% compared to 2015. For many catchments, this would be enough to meet current water quality objectives.
OLAW, one of 11 National Science Challenges that fund research aimed at solving NZ’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, phosphorus and sediment in 1995 and 2015, and what would be possible for future water quality in 2035 if every farm in NZ adopted every known mitigation.
This information is crucial to helping farmers in degraded catchments to 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 NZ catchments can get most of the way towards meeting the current water quality objectives,” OLAW chief scientist professor Richard McDowell says.
Despite the efforts of many farmers to care for our water, nitrogen loads have increased over the past 20 years because other farms have changed or intensified their production.
Land area used by dairy expanded 40% between 1995 and 2015, and total dairy production increased by around 160%. The land area occupied by sheep and beef contracted, but the intensity of production per hectare increased.
“Aotearoa’s freshwater quality is degraded, and in some areas much more than others,” he says.
“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.”
Just where nitrogen concentrations are heaviest and how that picture would change if all farmers adopted all on-farm mitigations to reduce nitrogen loss to water can now be seen on an interactive map available online (tinyurl.com/OLW-map), also funded by OLAW’s National Science Challenge.
“This map helps New Zealanders see where meeting limits is achievable, and where limits aren’t likely to be met under existing land use,” he says.
