Air curtain to improve water quality on Lake Waikopiro proving successful

Max Turnbull's farm borders Lake Tutira. Photo / Supplied

A trial aimed at tackling toxic water quality in Tutira has so far been a success but will need to be monitored over summer.

An air curtain was installed in Lake Waikopiro at the end of September as part of Te Waiu of Tutira (The Milk of Tutira) project, a partnership between Maungaharuru-Tangitū Trust and Hawke's Bay Regional Council (HBRC), to improve water quality and habitats in lakes Waikopiro and Tutira.

HBRC water quality scientist Dr Andy Hicks said the curtain has increased oxygen levels at the bottom of the lake from zero to 100 per cent.

Council scientists test the lake at least once a week and the curtain has been working well, he said.

However, the temperature will need to be monitored because the entire lake is at surface level temperature due to mixing from the air curtain.

"This could be a problem for trout, it's not ideal to have it too warm.

"We just need to monitor the fish population to see if we start to get any adverse effects on trout and then decide what to do from there."

If the lake got too warm it would not happen until February or March and it would not get warm enough to affect eels or tuna.

A decision would then be made as to whether it was better to have trout uncomfortable due to heat or to have all types of fish dying from lack of oxygen due to algal blooms, he said.

"From my perspective I'm pretty impressed with how it's working but the biggest drawback is the temperature."

The air curtain has already made an impact in diluting the lake's current algal bloom which occurred from nutrients from last year.

"We're going to watch that to see if it disappears."

If the Lake Waikopiro trial is successful, and all invested parties agree, an air curtain will be put into the larger, adjacent Lake Tutira.

This decision will be made after temperatures and the trout population is assessed at the end of summer.

The air curtain would be put into Lake Tutira in winter and turned on at the start of spring to ensure no algal blooms were already established.

An air curtain at both lakes would be a short term solution in helping the water quality but a strategic catchment management plan, which is being developed, will be aimed at ensuring long-term lake health.

"We need to try to reduce the nutrients going into the lake.

"This is an engineering fix, not a long-term solution. It's an ambulance at the bottom of a cliff."

Fourth generation Tutira farmer Max Turnbull, whose farm has bordered Lake Tutira for three generations, said he felt the air curtain was a positive step in improving the water quality which had deteriorated due to farming.

"From what I've been told the nutrients in the lake is almost 100 per cent due to farming back in the 1970s.

"I'd like to think modern farming practices in the district are a lot better.

"Adjoining land owners are making more of an effort than ever before to make sure their farms are impacting the lake as little as possible.

"The farmers in the area are doing their best and I hope they will continue to do that and more so."

Mr Turnbull has four paddocks that adjoin the lake and a significant number that adjoin a creek which has been earmarked to be diverted to run into the lake in the future.

Farming has changed at his 730ha Braes O' Mar farm to help and all water coming from the farm goes through a riparian strip before it gets to the lake, he said.

He also uses a phosphate rock-based fertiliser which is better for the environment than a chemical fertiliser.

A crew soon to harvest pine trees on his farm will do everything in their power to ensure minimal sediment flow into the lake, he said.

Many farmers in Tutira, including Mr Turnbull, had also started fencing off waterways.

The development of a catchment plan is also helping to ensure this, he said.

Most did not mind doing this even though fencing the land usually cost a fair amount, he said.

"It needs to be done...[the water quality] affects the community.

"Any farmer in the district would like the thought that it is a swimmable, healthy environment.

"I swam in it as a kid but I don't think many kids swim in it now and you never had to block your nose going past."

The area is one of six identified in the HBRC's annual plan as environment hot spots needing attention.

The air curtain involves pressurised air being pumped through a 50-metre pipe tethered close to the bottom of the lake and across the deepest part.

The air curtain increases oxygen levels at all depths throughout the lake by creating a circulation current, much like bubbles in a fish tank.