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Robust information needed to inform management of Waikato groundwaters

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Published: 12/08/2022

New groundwater research reveals that changes to land use and management may result in more rapid improvements to freshwater quality, says Waikato Regional Council.

The results of the research, funded by Waikato Regional Council, were presented at this week’s meeting of the council’s Environmental Performance Committee.

It was part of a wider report on groundwater nitrate levels and trends across the Waikato region.

Council Science Manager Dr Mike Scarsbrook said the council-funded research has shown shallow, younger groundwater is an important pathway for nitrogen moving from the land to waterways.

“We had previously considered older, deeper groundwater to be a major pathway in parts of the region. The good news is that our research indicates changes in land use and management will have more rapid responses in surface water than previously thought, and this has implications for upcoming changes in regional policy,” Dr Scarsbrook said.

The highest levels of groundwater nitrate in the Waikato region occur in the Pukekohe/Pukekawa and Matamata areas, due to market gardening and dairying.

Areas of low intensity land use – such as in Coromandel Peninsula, Taupō and the King Country – tend to have lower nitrate levels.

Overall, there was a 50:50 mix of degrading and improving trends over the last 20 years in the regional state of environment network of 110 wells. In contrast, a community supply network of 80 wells showed more degrading trends (23%) than improving (6%).

Dr Scarsbrook told councillors it is difficult to match trends to causes, but land use intensification is likely to be a major factor.

When it comes to compliance with current national drinking water standards, Dr Scarsbrook said nearly 12 per cent of regional wells exceed the standards (11.3 mg/l) and a further 20 per cent are more than half the Maximum Allowable Value (MAV) of 5.65 mg/l.

Less than 4 per cent of wells in the community network exceed MAV and none of these are now used for potable supply.