Mangrove mulching to resume in New Year

For immediate release: 24 December 2010

Bay of Plenty Regional Council will continue in the New Year to support the removal of mangroves from the existing consented areas. Mechanical mangrove removal will resume on the 19 January 2011 after it was stopped temporarily in August due to the bird breeding season.

The Council’s support of mangrove management in Tauranga Harbour is in recognition of sedimentation from land management practices - the primary contributor to mangrove spread.

Chair of the Waikareao Estuary Care Group Ross Steele said the work done so far in the Waikaereo Estuary is looking fantastic.

“We’ve been working towards this for so many years we’re elated to see it finally happen. We can’t wait to see it finished either,” said Mr Steele.

From the Waikareao Estuary the machine will be continuing on the Waimapu and Welcome Bay Estuaries before moving on to the Wainui Estuary at the end of Morton Prestige Rd.

Bay of Plenty Regional Council Estuary Care Officer Braden Rowson said 10 Estuary Care community groups hold consent to manage mangroves.

“Prior to council assisting this process with a special machine, the care groups were completing this arduous task by hand. A wide tracked digger with a mulching unit attached is now being used to clear the mangroves. The machine exerts approximately 2psi ground pressure – significantly less than a human footprint,” said Mr Rowson.

“It’s been a very big learning curve for us this last year,” Mr Rowson said. “We’ve been learning as we go, adjusting methods and doing a lot of monitoring to make sure we’re doing the right thing.”

Approximately 80 hectares have been removed to date with approximately another 30 hectares to go on the remaining sites.

The very fine mulch material produced is remaining on the bed decomposing on site which was unexpected.

Mr Rowson said residents close to the removal areas may notice an odour during, and for a while after the clearance.

“This is a result of disturbing the anaerobic estuary mud during the mulching process and the subsequent decomposition of the mulch which releases hydrogen sulphide (similar to the Rotorua geothermal smell).”

“Another learning was to do with the decomposing of the mulch. Decomposing organic matter strips oxygen out of the water column. An initial independent study indicated that this might be an issue but further monitoring analysis showed that there was no reason for concern and the dissolved oxygen levels are well within health guidelines,” said Mr Rowson.

Monitoring will continue as the project progresses. Other factors being monitored include estuarine habitat recovery and mangrove stump and root decomposition.

January will not only see the machine resume its work but also the Council team will experiment with picking up the mulch rather than leaving it on site.

ENDS

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