The path to recovery from Gita. Tasman Bay Guardians

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The path to recovery from Gita. Tasman Bay Guardians

Rob Davidson conducts a qualitative study of Torrent Bay Estuary after Cyclone Gita 2018

Tasman Bay Guardians

Since my last blog,  it’s been very busy times,  as well as running our Abel Tasman EcoTours hosting visitors,  students, conservation workers and even international diplomats,  we have been forming our aquatic environmental group Tasman Bay Guardians.  The Trust deeds are with the lawyer and now we wait for our application to be accepted.  In the meantime we have been supporting the Sustainable Marahau group, founded in teh wake of Cyclone Gita,  in working towards a smarter future to ensure the integrity of their lands and ecosystems.  This in turn benefits the health of Te Tai  o Aorere,  the Tasman Bay.  At the groups preliminary meeting it was identified that we need to set up an ecological study of the estuaries, which were smothered in silt and debris from the catchments.  It was necessary to determine a reference point to which recovery or further degradation could be measured.  And the report will also help the community in their quest for review of the land management practices above their homes.

So I called Rob Davidson,  who has decades of experience monitoring the Abel Tasman Marine Environment and he agreed undertake a study.  I approached NIWA Sustainable Seas Science Challenge who very generously donated funding for this community led initiative which fits nicely into the Ecosystem Based Management model they are currently trialling in Tasman Bay.  We collaborated to produce a survey of the Otuwhero Estuary, who’s catchment is primarily pre- and post-harvest forestry, and pastoral land, in comparison to Kaiteriteri estuary,  which is primarily pre-harvest and residential catchment,  and to Torrent Bay Estuary,  who’s catchment has remained relatively unmodified and is protected by the Abel Tasman National Park.   All three estuaries share the same Separation Point Granite soils and are adjacent to each other along the Western coastline of Tasman Bay.

Estuary Impact Report

Estuary Impact Report (Davidson, 2018)

The report found that the Otuwhero Estuary has become highly degraded as a result of the sedimentation,  with some herbfield permanently lost due to build up of silt.  Large areas were covered by woody debris and core samples showed that there was significant deposits of new fine silt.  Kaiteriteri was less affected, some evidence of fine sediment was there, however the catchment is unharvested.  This estuary is significant, ecologically but also iconically as it is adjacent to one of the most popular tourist destinations in the South Island,  who come for it’s outstanding scenic values.  The Torrent Bay Estuary was apparently unscathed, and remains at it has probably been for the last 150 years.

Surveying kaiteriteri estuary after cyclone gita. Tasman Bay Guardians

Rob Davidson conducts a qualitative study on Kaiteriteri Estuary after Cyclone Gita 2018.

survey on otuwhero estuary after cyclone gita. Tasman Bay Guardians

Rob Davidson conducts a qualitative study on Otuwhero Estuary after Cyclone Gita 2018

Conducting and esturay survey after cyclone gita. Tasman Bay Guardians

Rob Davidson conducts a qualitative study of Torrent Bay Estuary after Cyclone Gita 2018.

Recommendations

To paraphrase the recommendations in the report (Davidson 2018):

The Tasman District Council website states “Land disturbance occurs when the soil and covering vegetation is removed or disturbed. Land  disturbance may result in soil loss or damage, soil instability, sediment mobilisation and subsequent deposition and contamination of water ways (including underground cave systems). Such disturbances may adversely affect natural ecosystems or impact archaeological sites.” The TDC website also states “Separation Point Granites are readily eroded when exposed. Particular care is needed during earthworks and with storm-water control. Because of the highly erodible nature of the Separation Point Granites particular care is needed when undertaking any form of land disturbance. In particular, all storm water needs to be appropriately controlled and any areas of exposed soils stabilised.” The present investigation of three estuaries with Separation Point Granite soils confirms the two estuaries with modified catchments are being ecologically degraded. In Otuwhero Inlet, both Sections 11a and 11b of the New Zealand Coastal Policy Statement are contravened due to the adverse impacts documented during the present study. At Kaiteriteri Inlet, it is highly likely that adverse impacts will occur in the future when the catchment is disturbed during forestry harvesting activities coinciding with a major rainfall event.
To reduce further estuary degradation, carefully crafted integrated catchment management is required. Such a management Plan also requires “buy-in” from the catchment land owners. In particular, the Otuwhero catchment is large and will always carry significant sediment during large rainfall events, however, there are a number of activities exacerbating the  sediment issue (e.g. forestry harvests). Catchment activities that destabilise or expose the erodible soils need to be assessed and, where appropriate, regulated or retired. Activities such as establishment of riparian strips, retirement of land from farming, replanting of native vegetation and sediment controls should be funded and encouraged (Urlich, 2015). Such measures are not an overnight fix and form part of long-term catchment management programme aimed to ensure the ecologically integrity of these ecologically important Abel Tasman estuaries are not further degraded.

What this report means to Sustainable Marahau

In the words of Ross Morton from Sustainable Marahau:

“From Sustainable Marahau’s point of view, our intention was to conduct a non-biased study in order to see if our suspicions were correct or not, i.e. that the inlets downstream of areas under pine plantation were more susceptible to significant sedimentation and that this was having a negative environmental affect. In other words, we were after hard facts and evidence rather than supposition or assumption. As a result of having this evidence, we would hope that there be tighter controls on forestry practices in order to protect the natural environment. This is not about stopping forestry, it is about impelling NZ to adopt best international practice, or to create world leading new practices, that are much more sustainable than those currently being followed.”

 

surveying the damage from cyclone gita. Tasman Bay Guardians

Robert Palzer of Sustainable Marahau surveys the denuded catchment draining onto his land. The gum tree to his left was stripped of bark by flying logs brought down in the flood waters of cyclone Gita. 2018

Benefits to interested parties and citizen science.

The report has provided a benchmark for monitoring the hopeful recovery (or degradation) process of the estuary and the control sites.  A local family who are heavily involved in the restoration of the Otuwhero wetland have expressed interest in continuing on with the photo points designated in this study into the future.  Three generations of this family are passionate about this place and are learning new skills to be able to care for it.  We have provided the report to the Kaiteriteri reserve board,  who are also looking at how to best care for their Estuary,  and this has also lead to some attention from international entities involved in sustainable tourism overseas.  We have provided the report to iwi, Tasman District Council and the Department of Conservation who now have a tangible document on the impacts of catchment management and the storm in order to be able to make future decisions.  We hope that this report benefits the Sustainable Seas Science challenge,  which is a large and ambitious multi-agency project looking at the sustainable future management of our precious ocean ecosystem and resources.

Impacts to the bay.

Our last blog on this subject compelled a local resident of Tokongawa to send me this photograph two days ago of the last rain event.  We always used to talk about the Motueka River plume,  we now have an Otuwhero river plume.  How long will it be before we have a Kaiteriteri plume?  Regardless of the source,  this sediment all ends up in the sea, talks with fisheries managers have revealed that coastal trawlers are now not fishing in certain areas for fear of being ‘hung up’ in the mud.  This is a worrying sign,  and scuba dives I have done this summer have revealed a benthic turbidity layer on the seafloor,  which is essentially a perpetual cloud of fine silt suspended above the seafloor.  Anything that filter feeds (scallops, oysters,  mussels, bryozoans),  can not thrive in this environment,  and we are seeing a ‘regime shift’  favouring deposit feeders such as turret  shells and sea cucumbers,  which eat biological deposits in the mud.  We look forward to finding out more about this in the future as more studies are undertaken.  More mud equals less light leading to less photosynthesis and less seaweed and available food and habitat that maintains diversity.

otuwhero sediment plume. Tasman Bay Guardians

Tokongawa resident Robert Curtis felt compelled to send us this image of the mud plume coming from Otuwhero Estuary on Wed 16th May 2018. All that mud ends up on the sea bed.  Note Abel Tasman National Park in the background.

Abel Tasman Tree Collective – Come and plant a tree!

Part of our work in eco-tourism is to encourage visitors to invest in the environmental protection of the region they have come to enjoy.  We founded the Abel Tasman Tree Collective in late 2017 as a way for visitors to offset their carbon emissions while travelling to and around our beautiful country.  Our small collective of local operators have done pretty well in our first season,  managing to acquire around 900 native trees and grasses to be planted.  We are very excited to announce that our first community  tree planting will be happening in Marahau on Sunday 20th May.  We hope it will be well attended and a way for the wider community to acknowledge that we all need to look after this fragile ecosystem, and to come and see up close the impacts that this event has had on the ecosystem. It is a small token for what seems like an impossible task,  but we hope that this will be the first of much larger things to come,  that will engage Treaty Partners, residents, local businesses,  large corporations, government and visitors to the region in helping to heal the wounds left on the land.

inspecting tree planting site. Tasman Bay Guardians

Stephen Tate of Marahau Valley farm and Myles Gwynn of Garden Organics survey the new riparian strip ready for planting by the Abel Tasman Tree Collective.

Conclusion

We only have one environment,  if we mess this one up there are no second chances,  New Zealand has built a global reputation on being ‘clean and green 100% pure’.  This is an amazing place and all that live here are kaitiaki or guardians.  In the mid 1930’s the NZ government wanted to build a road from Marahau to Torrent Bay (now in the Abel Tasman),  a staunch lady called Perrinne Moncrieff resisted this and gifted her family land to the crown to form the basis of the national park.  This lady managed to achieve the eviction of the farmers to make way for the national park,  in the middle of the Second World War!  This bold action by her and her colleagues has left a world class legacy that visitors come from far and wide to enjoy.  Millions of dollars are injected into the local economy year after year as a result of this bold move, creating employment for thousands.  This is the time to look at that story and see how we can leave a legacy like that for the next generation that doesn’t rely solely on getting all we can from the land.  I wonder if Perrine realised that by protecting the land,  she has protected the estuaries and the sea adjacent to the coast and our Abel Tasman community.  We just need to afford the same respect to more of our land,  it’s all connected and so we need to be.  We are not anti-primary industry, we believe that everyone has the right to earn a living.  But we should work together in doing it the right way and not at the expense of our environment.  The next storm is only just around the corner,  can we give our fragile lands a rest and help them heal so that they can help heal us.

pristine abel tasman beach, tasman bay guardians

As you leave the roads and head into the Abel Tasman National Park, the sea changes from brown to green to turquoise blue. This photo was taken in May 2018. The turquoise waters are as much Mrs Moncrieff’s legacy as the regenerating native forests.

4 Comments

  1. Claire says:

    Great report, thank you

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