Alarm bells at Ashburton lakes

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By Toni Williams

Results of a Department of Conservation (DOC) restoration and conservation project on the Ashburton Lakes are ringing alarm bells for the Ashburton Water Zone Committee.

One member, Ben Curry, said there was the potential for water quality to tip over.

A report on the project was given to water zone committee members last week by DOC aquatic unit principal freshwater scientist Hugh Robertson, of Nelson, and freshwater technical team member Tom Drinan, of Hamilton.

It was an update on the state and trend of water quality in the Ashburton Lakes district, and the streams of the Maori Lakes catchment. They included Heron, Camp and Clearwater, Emily, Maori, and Denny lakes with Clent Hills, Gentlemen Smith, Jacobs streams, Maori Lakes and Paddle Hill Creek.

Summary of the results from water quality monitoring data indicate trends, especially with nitrogen increase, were a cause for concern at a number of sites.

Total phosphorus, Chlorophyll A and total suspended solids results were also given.

There was “quite a bit of spread in the data across the individual lakes” but annual medians showed levels of total nitrogen in the Lake Clearwater, Lake Emma and Maori Lake (front) had a “moderate degree of impact”, Mr Drinan said.

“Some lakes have more data available than others.”

“Trends are starting to emerge for Lake Heron, previously in an A band (higher water quality)…but more recently nitrogen concentrations have increased (declined) into a B band.”

He said there was also “quite a bit of fluctuation” between A and B for Maori Lakes east and west.

Discussion was held around the data measuring, the values used, seasonal differences and water bird waste versus farm issue.

Mr Robertson said there were studies that showed water-bird contaminant was limited and the majority was linked to land use.

He said there were many ways of measuring lake health, including traffic status, nitrogen, phosphorus, checking aquatic plants, water quality, hydrological regimens, modelling, indicator species and cultural assessments.

“No-one indicator really can summarise the (lake) health. Often there is a real focus on water quality but you actually need to think about lots of different components.”

Risks to lake health included eutrophication (excessive richness in nutrients), water clarity, hydrological change, less flow (less flush of nutrients) and increased pest fish such as perch, which contributed to quality issues and native species being displaced.

DOC sought action from the committee to help work with Environment Canterbury and landowners to reduce the loss of nitrogen and phosphorus sediment to streams in the outer vulnerable lakes, such as Maori, Heron, Camp and Clearwater.

As well as a focus on the management of nitrogen – which had the largest rate of increase – in the lakes and streams to make the ecological health of the lakes and streams was adequately addressed in farm environment plans.

Zone committee member Ben Curry said “there’s a bit of an alarm bell ringing here” with potential for the lakes water quality to “tip over to a point they’re buggered”.

The committee sought to get information from ECan on the existing work being done with affected stakeholders.

Mr Robertson has worked in the Ashburton Lakes district on the O tu Wharekai project, one of three projects in the national Arawai Kakariki Wetland Restoration Programme, since 2008 providing scientific support.

The programme started nationwide in 2007 and has a national budget of $1.6m a year, including around $250,000 for scientific research and monitoring.

It will continue until, at least, 2025.