Environment Southland has said it found no specific cause for nitrate spikes in Gore’s drinking water supply last year. Other statements by the council about nitrate contamination across the region’s groundwater — which supplies many people’s drinking water — have indicated causation is complex, multiple and has time lags.
University of Otago public health and water expert Marnie Prickett said it was "really important to focus on protecting people’s source water and I don’t like seeing council communications kind of jump around to deflect the conversation away from that fundamental responsibility," she said.
A statement by the council last November had said its investigation into Gore’s water supply — which had nitrate spikes above the maximum limit for safe drinking — was "complete and hasn’t identified a specific cause".
The council said the pollution was "likely to be the result of intensive land use in the area", but the phrase was not explained.
A nitrate pollution report commissioned by the council and dated January — but publicised by the council this week after questions from the Otago Daily Times — said nitrate contamination is widespread. It finger-pointed dairying as a leading cause of nitrogen losses and recommended "reducing nitrogen losses in areas of known susceptibility".
However, in answers to the ODT about the report, the council repeated it had "not determined" the cause of Gore’s nitrate spikes and the issue across Southland was "vulnerable aquifer setting overlain by higher risk land use activities".
Council general manager for science Karen Wilson provided a list of "higher risk" activities — including the "intensive land uses" of dairying, winter grazing, arable and horticulture — but did not suggest which had any, or worst, impact on current nitrate pollution.
Monitoring nitrate in groundwater was "complex", Ms Wilson said.
"At any point, nitrate in an aquifer will be comprised of a range of sources, and over a range of time periods due to the lag time between land use and contaminants entering and moving through groundwater. This makes any investigation into the cause of nitrate changes in groundwater extremely complicated. We are continuing to do further work on better understanding the situation at Gore."
Otago’s Ms Prickett said there were ways of testing nitrate sources. The council’s January report made it clear that, in Gore, intensive winter grazing was "under the spotlight. It can result in very high loss of nitrates and other contaminants".
"You can find out exactly the source of nitrate ... and the report strongly indicates that intensive winter grazing is linked to it and we have known for a long time that you get a lot of pollution out of areas being intensively winter grazed."
"If they [Environment Southland] are saying they do not know the cause then they must determine it. How will they protect the people of Gore and their drinking water if they have not determined the cause all these months later? We know there are number of places that nitrate can come from but they should be looking at determining the primary contributor and how to manage that.
"Jumping around saying it could be this or that is not good enough and if they don’t know exactly they should be mitigating risks in advance by tackling the most likely thing ... They have a responsibility to protect that aquifer."
Talking about lag times was a "deflection", Ms Prickett said.
When pressed by the ODT, Ms Wilson made a statement again mentioning "lag effects" but acknowledged dairy farming has been the "dominant form of agricultural intensification" and a subsequent increase in livestock and nitrogen inputs "aligns with regional scale patterns and trends we are seeing in vulnerable aquifers".
She defined winter grazing as grazing stock, including dairy cows, on forage crops such as brassica, but said the council did not have "data at hand to estimate the proportion of winter grazing that can be attributed to the dairy industry specifically".
The report would form the basis of "councillor discussions and our ongoing approach to tackling this issue" but there was no "quick fix".
A workshop for councillors would happen.
Council was "reviewing" its planning framework, noting the national pause on plan changes.
In response to Ms Prickett’s points, Ms Wilson said she welcomed engagement.
