Widespread degradation of Southland’s drinking water safety has been exposed in a council-commissioned report.
The Environment Southland report maps an increase in nitrate-containing groundwater — which can cause illness and death at elevated levels — and points the finger largely at a rise in intensive farming, notably dairy.
Groundwater is the source of many people’s drinking water across Southland.
The report sparked calls from University of Otago public health and water academic Marnie Prickett and environmental organisation Greenpeace for the council to announce a nitrate emergency and reduce intensive dairy farming.
Ms Prickett said the report, titled “Nitrogen Contamination in Southland Groundwater”, was “comprehensive, clear and the news is not good. It shows a concerning nitrate problem”.
“Declaring a nitrate emergency is a first step that must be followed by a clear pathway out of this serious problem. We could investigate more but this is not going to change the material outcomes needed,” Ms Prickett said.
Intensive dairy farming and the nitrate contamination from urinating cows was a key cause, including when cows were winter-grazed on crops planted on bare earth that could not soak up nitrogen, Ms Prickett said.
“This report draws the link between periods of winter grazing and pulses of nitrogen going into groundwater used for drinking water,” she said.
Ms Prickett called for an independent and peer-reviewed inquiry into the council’s land-use rules, plus a review of the council’s monitoring methods to enable enforcement.
She also called for a review by the auditor-general of processes to prevent any conflicts of interest held by councillors and council staff that could impact decision-making about land use.
Greenpeace freshwater campaigner Will Appelbe said a nitrate emergency should be declared “as a minimum”.
Action should include “preventing any further dairy industry expansion, reducing the size of the dairy herd and moving away from dairy farming altogether to protect access to safe drinking water”, he said.
Chairman of freshwater science at the University of Otago Prof Ross Thompson also linked nitrate and farming intensification and said the issue was of “environmental and public health concern, and requires urgent attention”.
Environment Southland has not, until now, flagged the report publicly — despite it being labelled as having been “issued” on January 30.
The Otago Daily Times spotted it among other documents filed in a science report portal and posed questions to the council — which said it could not respond by deadline.
The council then pushed out a media release acknowledging many Southland sites had “long-term deteriorating trends” of nitrate contamination, caused by a combination of “intensive land use” and the region’s shallow water table, meaning aquifers were “vulnerable”.
The release said the problem could take decades to fix — and dairy farming was not mentioned.
Environment Southland general manager science Karen Wilson described reducing the contamination as a “challenge”.
A council source said, as far as they knew, there had been “no communication prior to the release about the report’s findings internally”.
The maximum allowable nitrate in drinking water is 11.3mg/L, but the National College of Midwives has warned pregnant women about levels exceeding 5mg/L risking preterm birth and low birthweights and public health academics have said levels below this may be a concern, including as a cause of colorectal cancer.
Ms Prickett said any level above 3.5mg/L was indicative of “serious degradation of environmental health let alone public health”.
In the council report, the location of drinking water supply wells — including council-run and privately operated wells — is mapped alongside predicted nitrate concentrations in groundwater 10m below land surface.
Overall, 612 (44%) of domestic supply wells and 18 (45%) registered public drinking-water supplies were located “within areas classified as having high vulnerability to nitrate contamination” and were used by an estimated 13,632 people on public groundwater supplies and 1530 people on private supplies.
There were deteriorating trends and vulnerability hot spots included Balfour and the Waimea Plains, Knapdale supplying Gore and the Central Plains and Waimatuku.
Only 1% of domestic wells mapped were in areas predicted to have nitrate concentrations below 1mg/L and almost half (49%) were in areas predicted to have concentrations within a range of 3.5 to 8.5mg/L, with a further 5% predicted to exceed 8.5mg/L, with some of these above 11.3mg/L.
In many parts of Southland, the report draws a link between higher nitrates and dairy farming, winter grazing being described as a “high-risk pathway for nitrogen leaching”.