Caution urged as nitrate research continues

A group of Waimakariri farmers are hoping to assist Environment Canterbury in getting a better understanding of the state of local groundwater.

The Waimakariri Landcare Trust has been in talks with Environment Canterbury about working together to conduct nitrate testing later this year on the district’s groundwater.

Environment Canterbury’s 2023 groundwater survey, of 349 wells across Canterbury, was released earlier this month and showed high nitrate levels and E. coli in some water sources.

Recent water testing by Greenpeace has also raised alarm bells.

But Oxford dairy farmer and trustee Cameron Henderson said the sample sizes were too small to give a clear understanding of the state of groundwater.

He hoped testing would be conducted during the next irrigation season.

"We want to build a better picture of where the nitrates are coming from."

Mr Henderson said there was "no disputing the data" about nitrate levels in groundwater, but more testing was needed before drawing conclusions.

"We know there are high levels of nitrates in some areas, but is it dairying?

"It might end up being dairying, but we don’t want to point the finger in the wrong direction before we have enough data."

He said the dairy boom in the Waimakariri district was "a 20 to 30-year phenomenon", but the "lag time" of groundwater flowing downstream meant some of the nitrate contamination could date back much earlier.

Scientific studies showed groundwater had a "lag time" of 50 years or more to flow downstream before feeding aquifers in Kaiapoi, Belfast and Christchurch.

Environment Canterbury acting groundwater science manager Davina McNickel said nitrate levels appeared to be increasing in 59% of the wells surveyed, with only 17% likely decreasing.

"Groundwater quality results do not show any clear improvement or reversal of increasing trends in nitrate concentrations. Efforts to change land use and farming practices over the past 10 years were designed to reduce nitrogen concentrations in our groundwater.

"However, it will take many years before we start to see reductions in nitrates in groundwater as a result of these efforts."

Mr Henderson said farmers had changed their farming operations since the development of the Waimakariri Zone Implementation Plan Addendum (Plan Change 7) to the Canterbury Land and Water Regional Plan, which came into effect in September. Environment Canterbury’s latest annual groundwater survey detected E. coli in 32 water sources and there were 35 water samples with nitrate-nitrogen concentrations above 11.3mg/l.

 - LDR is local body journalism co-funded by RNZ and NZ On Air.


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