Monday, February 26, 2024

E coli plagues NZ’s freshwater systems

Avatar photo
Baseline study of 850 sites sketches magnitude of freshwater task ahead.
Reading Time: 3 minutes

Bacterial contamination is the main issue facing New Zealand’s freshwater systems, and every region in the country has at least one major contaminant that needs to be reduced to meet the country’s freshwater standards.

A new report from Our Land and Water highlights the current levels of the key contaminants E coli, nitrogen, phosphate and sediment in rivers, lakes and estuaries across NZ. 

Since the National Policy Statement (NPS) on Freshwater Management, this report is the first to establish the base level for the contaminants and by default how much work is required to meet the NPS standards.

Three-quarters of the country’s catchments are contributing more E coli to water than allowable under NPS standards, and the affected area is significantly greater than for the other three contaminants. 

The report also found there is considerable variation both within and between catchments in terms of which contaminants are greatest.

Waikato and Manawatū take the dubious title for the highest level of E coli contamination, requiring a 90% reduction to meet the standards, followed closely by Gisborne, Northland, Auckland and Taranaki. 

Research lead Dr Ton Snelder said reducing E coli contamination to an acceptable level is made more challenging when largely untouched conservation land is removed from consideration, focusing efforts on modified landscapes, particularly land used for food production.

He also noted that every region in the country has at least one contaminant that has to be reduced to meet the standards.

Nitrogen levels, long the focus of the farming sector’s efforts, are most excessive in Canterbury and Southland. They have to reduce their nitrogen loads by 44% and 41%, respectively, and Otago by 33%. 

Perhaps surprisingly given its dairying concentrations, the reduction required in Waikato is only 6%.

When it comes to phosphate, Otago requires a 13% reduction, and Manawatū and Southland 12% each. 

Often moving in step with phosphorous levels, Otago also requires the greatest reduction for sediment with a 338% load reduction required. 

That high level is driven by upstream reductions being larger than the load at the bottom of a catchment, due to sediment being deposited in lakes or floodplains as it is carried downstream, such as along the Kawerau River.

Otago is trailed by Manawatū, which needs a 58% reduction, Canterbury 49%  and Waikato a 47% reduction in sediment.

Of all the regions, the West Coast has the lowest level of reduction required, while Manawatuū-Whanganui will require the most work in reducing all four contaminants.

The study was based upon 850 sites monitored by regional councils nationally, and modelled up to capture 650,000 river segments, 960 lakes and 419 estuaries. 

Its authors acknowledge the uncertainty of modelling, but place 95% confidence upon the estimates.

Snelder confirmed reductions of 30% or more in the contaminants are unlikely to be achieved without some changes to current land uses in such catchments.

“These are not terribly surprising results. What is novel and perhaps somewhat surprising is the proportion of land area affected by the levels. Large areas of NZ need to be considered to achieve these regulatory limits.”

OLW director Dr Jenny Webster-Brown said she hopes the report will not be interpreted as a call for a revision or re-think of national standards.

“It is simply an account of what we need to do to achieve them,” she said. 

She said there are some regions, including Canterbury, that are going to find it a significant challenge to meet their nitrogen limits.

“It has to be taken on a regional case-by-case basis.”
OLW director Professor Richard McDowell acknowledged the impact farmers have already had on lowering their nitrogen impact on waterways.

“If farmers had not done what they have in the past 10 years our nitrogen and phosphate loads would be 50-90% greater than they are today.”

The report comes out as the new coalition government has announced it will replace the NPS for Freshwater Management to better reflect the interests of all water users. In the coalition agreement with the ACT party, it has been agreed to change the freshwater rules to exempt councils from obligations under the NPS.

Webster-Brown said she would not wish to presume what the new government is going to do, but she noted that the original NPS was inspired by National, with NZ First input, back in 2011.

“I would like to think our current coalition government will not be tempted to throw the baby out with the bathwater. It would be hugely damaging on the progress we have made with our freshwater systems.”

People are also reading