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Lakes' water quality concerns deepen

Lakes' water quality concerns deepen

There is trouble in the waters of Ōtūwharekai (Ashburton Lakes).
Water sampling at Ōtūwharekai over the past year shows the water quality continues to decline.
The water monitoring results were recently presented to the Ashburton Water Zone Committee by Environment Canterbury (ECan) and the Department of Conservation (DOC), who are part of the Ōtūwharekai Working Group to restore lake health and cultural values.
ECan director of science, Dr Tim Davie, said the results generally show increasing nutrients and algae, which are causing worsening water quality over the past 10 years across the different lakes and streams of the unique sub-alpine catchment.
“Work is already under way to reduce nutrients entering the waterways from farming activity, and the nearby long-drop toilets in the huts settlement have been decommissioned.
“However, these actions could take some time to make a difference to water quality results.”
Ōtūwharekai features a series of small to medium-sized lakes and streams in the high country, which Davie said means results often fluctuate from year to year due to climate conditions and other variables.
“It was pleasing to see Te-Puna-a-Taka/Lake Clearwater decrease in algae biomass this summer, but it’s too early to say if this is a pause in decline or reversal of the degrading trend,” he said.
“On the other hand, Ōtūroto/Lake Heron is showing a continued increase in algae, and high numbers of the nuisance algae ceratium, which is very good at out-competing other algae for nutrients.”
All of the lakes remain above their Trophic Level Index (TLI) limit, measuring overall lake health by assessing nitrogen and phosphorus (nutrients) and algal biomass (algae), which means they are not meeting the outcomes for freshwater health expected by the community.
Nitrogen concentrations in the streams have increased significantly in the Ōtūwharekai catchment in the past 10 years.
DOC technical advisor – freshwater, Dr Tom Drinan, said at most sample sites there has been a “two to three-fold increase in nitrogen concentrations”.
“These worsening nitrogen concentrations continue to pose a risk to the ecological health of these streams and the lakes and rivers they flow into.”

Help on the horizon
The monitoring of Ōtūwharekai could be greatly improved if Aoraki Environmental Consultancy Limited is successful with its funding application to the Ministry for the Environment for its Ōtūwharekai Mātauranga Māori Cultural Monitoring Programme.
The monitoring programme will see sensors installed in the area that will feed real-time water quality data to the Ōtūwharekai Working Group partners.
ECan director of science, Dr Tim Davie said the digital experience of the live-data capture from the installation of the sensors “will enable mana whenua and wider whānau to have real-time, 24-hr visibility of the health of the truly unique environment that is their taonga”.
The project also ties directly into the effort being made by the Ōtūwharekai Working Group he said.
“This joint programme, initiated by Te Rūnanga o Arowhenua, Te Taumutu Rūnanga and Te Ngāi Tūāhuriri Rūnanga, has led to work to specifically address high nutrient levels in Ōtūwharekai Lakes.
“As this work programme progresses, it will be important to track the improvements in lake health through both a science monitoring and mātauranga lens.”
Real-time monitoring will provide a much finer timeline of environmental measurements which aid in water management, he said.
“We already have some real-time water quality monitoring in place in the Ōtūwharekai area, including the nitrate logger in Gentleman Smith Stream and chlorophyll-a monitor in Te Puna a Taka/Lake Clearwater.
“What is being proposed by te rūnanga would significantly add to this monitoring network.”
Even if the real-time monitoring project does get the green light, Davie said ECan will continue to do its sporadic testing as long-term records are critical in water management and not all parameters can be monitored in real-time.
“For instance, total nitrogen concentrations and phosphorus concentrations at levels which occur in New Zealand waterways cannot be monitored real-time with current technology.”

  • By Jonathan Leask