Local Govt | National News Video | Parliament Headlines | Politics Headlines | Search


Groundwater an long term problem for Rotorua lakes

Groundwater an long term problem for Rotorua lakes

Lake Rotorua’s water quality is likely to get worse before it gets better because of large stores of nitrogen-rich underground water.

A new study commissioned by Environment Bay of Plenty has revealed that most of the groundwater currently entering the lake is too old to reflect the land development and intensification of agriculture in the Rotorua catchment after World War Two.

“Unfortunately, that means the poorer quality water is still underground and will not reach the lake for several decades. We’ve actually seen only the beginning of the problem,” says Paul Dell, Environment Bay of Plenty’s group manager regulation and resource management.

The results have major implications for future lake quality, he says. “It means we can expect quite dramatic increases in nutrients, particularly nitrogen, in the lakes over the coming years – unless ways are found to manage the increasing nutrient loads.”

The study by the Institute of Geological and Nuclear Sciences confirms what regional council scientists suspected – a time delay between land use and its effect on lake water quality.

Agriculture produces excess nutrients (nitrogen and phosphorus), some of which will wash over the top of the land and fairly quickly into nearby waterways. However a lot seeps down through the soil and mixes with water stored in large underground aquifers. Eventually, this nutrient-loaded groundwater will emerge through springs, which flow into the streams feeding the lake, or flow directly to the lake.

For the study, the institute measured the age and proportion of young and old water discharging from these springs and streams, mostly of which are located on the western side of Lake Rotorua.

Initial results show the mean age of the water ranging from 30 years to 170 years. The mean age of water in Hamurana Spring, for example, is 145 years. Only 18% of the flow is young enough to show the effects of agriculture. At the moment, Hamurana Spring contributes about 64 tonnes of nitrogen annually to Lake Rotorua. Scientists expect this to double in the next 50 years as nutrient-loaded water starts to flow through.

At Taniwha Springs, the mean age of water is 64 years, just under half of it being “young” impacted groundwater.

This study is the first part of wider investigations to understand the interactions, time delays and water chemistry of the groundwater system in the Lake Rotorua catchment. Scientists are also investigating groundwater in Lake Okareka.

© Scoop Media

Parliament Headlines | Politics Headlines | Regional Headlines

Gordon Campbell: On The Politics Of Scaring Voters Back Into Line

Fear has always been a useful mobilising tool in politics… yet in 2017, bogeymen of all shapes and sizes seem to have fallen on hard times. For years, the National party had painted itself as being the only reliable defensive bastion against the terrifying prospect of a centre-left government…

In fact, the polls suggest that the public seems to quite like the new government, its Prime Minister, and its proposed plan of action. Somehow, even though a Labour/Greens/NZ First government is in power, the sun is still rising and setting, on time. More>>


Gordon Campbell: On Drinking Water As A Failure Of Political Leadership

It is almost possible to feel sorry for the Health Ministry in their terrible, no good, very bad week... More>>


Gordon Campbell: On Saying ‘Work For The Dole,’ Nicely

As New Zealand First learned the hard way from its two previous periods in government, small parties in MMP coalitions get blamed for the unpopular stuff done by their senior partner in power, but no one remembers the good stuff the junior player brought to the table... More>>


Seismic Blasting: Greenpeace Launches Legal Challenge Against Amazon Warrior

A legal challenge against the world’s largest seismic oil exploration ship was launched at a public rally on Parliament Lawn. More>>


Tertiary: 80,000 People Eligible For Fees Free

The Government has today made good on its 100-day promise of delivering the first year of fees-free post school training and education and industry training from 1 January next year, says Education Minister Chris Hipkins. More>>


PM's Presser: Rebuilding Cathedrals, Felling Trees

Prime Minister Jacinda Ardern attended the press conference today with Minister for Greater Christchurch Regeneration Dr Megan Woods to announce urgent legislation this week for the rebuilding of the Christ Church Cathedral. More>>





Featured InfoPages