Thursday, December 7, 2023

Mixed results in Waikato environment report

Avatar photo
Decades of rising levels of nitrogen and bacteria in waterways identified, but Lake Taupō doing better than expected.
Two-thirds of northern Waikato aquifers show increases in nitrates, says a report on groundwater nitrates. File photo
Reading Time: 3 minutes

A report on the state of Waikato’s environment has good and bad news for the region’s waterways.

The State of the Environment report by the Waikato Regional Council identifies degradation of the region’s waterways, stream ecosystems, wetlands and forests caused by increases in nitrogen levels.

But there have also been improvements – phosphorus discharges to waterways are decreasing and air quality is improving. Lake Taupō is also doing better than expected, and sooner than had been anticipated.

The council’s hydrology and groundwater team leader, Dr Thomas Wilding, said the report was produced to enable an “open and honest conversation about what we have, what we are at risk of losing, and what we can do about it”.

“Our report provides an evidence-based picture of the major environmental issues facing the region, as well as recommendations on how environmental outcomes can be improved which will be helpful for developing policies and supporting actions.”

Gaps in the council’s state of the environment monitoring have also been identified, such as in wetlands, forests, biosecurity, geothermal and coastal waters.

Wilding acknowledged there are some limitations to the report.

“The changes reported here are limited to the changes we monitor, and freshwater quantity and quantity has been a focus of our state of the environment monitoring.”

The report says diffuse N levels have continued to worsen in many waterbodies. 

“All monitored tributaries of the Waikato River from Taupō to Karāpiro also recorded worsening nitrogen trends for the period 1990 to 2020,” it says. 

However, nitrogen concentrations have decreased in some areas where dairy farming is long established, such as monitoring wells and streams in the Hamilton basin. The report believes that in these deep aquifers that lack oxygen, denitrification can eliminate nitrate from groundwater.

The report also highlights that there has been no reduction in bacteria levels over the past 30 years, despite efforts by farmers to fence off waterways and the planting of streambanks. It calls the result “surprising”, saying uneven surface runoff is a possible explanation for the high bacteria levels.

“When soils become compacted from high stock pressure, their ability to intercept faeces, urine and fertiliser is compromised. Intense rainfall on steep soils with low infiltration capacity is more likely to generate surface runoff, carrying sediment and attached bacteria with it.

“If surface runoff was evenly distributed through the stream network, bacteria levels would be expected to reduce over time with the increasing length of streams fenced and planted. But surface runoff is not evenly spread – one study found 5% of land area generated 50% of sediment yield. For bacteria attached to sediment, concentrated overland flow is an effective transport pathway,” it says.

The report says the lack of improvement in faecal bacteria shows more work is needed to control potential sources of faecal bacteria.

While stock exclusion and improved farm dairy effluent management should continue to be primary mitigation actions in farm plans, it recommends extending actions to include better management of other critical source areas, such as tracks, raceways and intensive grazing of crops.

Council deputy chair Bruce Clarkson said it is important to councillors that issues raised in the report result in actions. 

“The Environmental Performance Committee has been charged by councillors with providing a work programme in response to the findings in the report within the next six months.

“This report provides a sobering picture of the degradation to our environment that has occurred over many, many years.

“While it’s pleasing to see some improvements, these are complex problems that have been identified through the report, and it will be essential that we work with those impacted, undertake scientific investigation and modelling to formulate meaningful actions.”

People are also reading