Fears over mangrove 'dead zones' heard

Forest and Bird members have succeeded in lobbying Bay of Plenty Regional Council to look at other ways of removing mangrove mulch after voicing their concerns over "dead zones" left in cleared areas.
The agreement was made after the group met with council representatives on Friday at the Waikareao Estuary, where members had earlier shown the Bay of Plenty Times an area they said had not recovered from mangroves being mulched four months before.
The group had called for the council to halt the mechanical removal of the remaining 30ha of mangroves in its programme, over fears it was creating "dead zones" or oxygen-depleted areas, where many different species such as titiko mud snails and crabs could not live.
The concerns were earlier raised by the National Institute of Water and Atmosphere (Niwa), which has been monitoring mangrove removal in the estuary as well as at Matua, Waikaraka, Te Puna and Omokoroa.
The council has now acknowledged that in some areas where there was limited tidal flow and a higher density of mangroves, these combined conditions had hampered the flushing of the mulch.
The council agreed to carry out trials on ways of removing the mulch during the next stage of the mulching operations that are due to start.
While the council will go ahead with the rest of its removal programme, set to begin next week, it has agreed to trial methods for removing mulch left behind.
In its first trial, the council will try collecting the mulch with a machine that has been previously used to remove sea lettuce from the harbour. As requested by Forest and Bird, the council said it would also seek independent scientific monitoring of some of the areas to get more information on the condition of the estuaries that have been mulched.
Forest and Bird recommended that Niwa undertake the work as the organisation was already undertaking a research study of mangrove removal areas within the harbour as part of a six-year research project.
The council has also agreed to investigate options for removing mulch in areas cleared last year to help speed up the process of re-establishing the historic sandflat habitats.
Bay of Plenty Regional Council chairman John Cronin said the rest of the mangrove removal would allow the council to trial various mulch removal options, "which will bring huge benefits to our community and help address Forest and Bird's concerns".
"In doing this, we will be looking at how we can speed up the recovery process, including carrying out trials on removing mulch on already cleared sites and those consented areas yet to be cleared.
"We're willing to engage and work with the estuary care groups and Forest and Bird about options and they're welcome to observe and comment on these."