Jane Nees BOP Regional Councillor www.janenees.co.nz

Recently there have been claims in the media that in some areas where mulching of mangroves has occurred in the Tauranga harbour and the mulch has not been mobilised and flushed out by the tide, that a dead zone has resulted.

This is not so. There is life, but it is not the life that we would want to see in our estuarine environment because it doesn't yet signal a return of the original ecology pre-mangroves. What we want to see eventually in these areas is a return of our sandy foreshore with the shellfish and seagrass that we associate with this. We recognise that this may take some time, and some areas will recover much more quickly than others because of the method used to remove the mangroves, the density of the mangroves and the strength of the current flow – among many other variables.

Last week, members of the public, estuary care groups, Royal Forest and Bird and NIWA met with staff and councillors from the Bay of Plenty Regional Council to look at an area of concern in the Waikareao Estuary. This area was cleared of mangroves by mulching in February and is not showing much sign of recovery yet. The mix of mulch material and sediment is black and anoxic (lacking in oxygen) – the result of bacteria using up all the oxygen as they act on the mulch material. This happens particularly when organic matter loading is high, the temperature is elevated and the estuary is not well flushed.

Healthy sediment must have enough oxygen to support the many estuarine fauna living on and within it. Lack of oxygen in sediments is toxic to a wide range of aquatic organisms. It also promotes release of ammonium and phosphate which can fuel algal growth. This is what we saw in the Waikareao Estuary. The sediment is overlaid with a carpet of various types of algae which are perpetuating the problem – and while there were a few crabs there is not yet evidence of a return of shellfish. The algal mat also prevents the muddy sediments being flushed by the tide, and is therefore slowing the return of a sandy seabed.

The regional council will be working with various interested parties to find ways to speed the return of these sediments to a healthy state. This will include looking at ways to remove the algae and mulch to enable the faster recovery of the sandy estuarine environment. It will also mean rethinking the way we remove mangroves in areas where we suspect conditions are not suitable for mulching.

In some areas, the current methods have been very successful. But, if there is a better way, we want to find it. You can be sure that we all want the very best for our harbour, and will work hard to find a sustainable solution for the future.

If you have any views on this or any other issue, please contact me on neesj@xtra.co.nz or ring me on 07 579-5150. Or you can check out my website at www.janenees.co.nz