Sediment and run-off putting squeeze on Havelock Estuary
The health of Havelock Estuary is continue to deteriorate, leading a councillor to ask what is being done to improve its condition.
A recent report on the Havelock Estuary written for the Marlborough District Council said the estuary was in "moderate to poor" ecological health, with sedimentation and high nutrients the main factors contributing to its poor state. Sedimentation had been a "high risk" factor since 2001.
The Havelock Estuary state of the environment monitoring report was presented to the environment committee meeting last week.
Councillor Jamie Arbuckle said he had seen monitoring reports come before council for the past nine years and they had outlined the estuary's deterioration.
* Havelock water systems vulnerable to sea level rise
* Marlborough District Council 'on top of' historic landfill sites
* The battle between industry and environment in Marlborough Sounds ward
Arbuckle asked what individuals and the community could do to get involved and "turn this around?"
Environment committee chairman Gerald Hope told the Marlborough Express outside the meeting the "estuarine change" had been brought about by the impacts of early felling of forests and conversion to pastoral farming.
"We have got to control the runoff of sediment into the rivers and into the Sounds," Hope said.
The council was concerned about the loss of biodiversity as a result of sedimentation, he said.
But change was going to take a "very long time" for things to settle and stabilise in the estuary, he said.
The report summary said the main cause for concern was around sedimentation and "high mud content".
Monitoring of the estuary in January found the estuary was at "moderate risk" of sedimentation, habitat loss and eutrophication. Eutrophrication is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae. This can lead to the depletion of oxygen in the water body.
The report said elevated nutrient and sediment loads from the catchment were the main cause of the "low ecological health".
Most indicators were unchanged from previous years monitoring.
A report presented to the council in 2017 found estuaries in the Marlborough Sounds were some of the muddiest in the country.
Dr Ben Robertson, who was contracted to write the report, said he saw three possible remedial actions to address the "big issue" of sedimentation. The first was to try and limit the flow of sediment into the catchment.
"Secondly you could try and physically remove the sediments, but that will be fraught with a few caveats both in terms of the economic and ecological impacts.
"Thirdly and probably the most favourable way forward would be to plant sediment trapping vegetation at known key points in the estuary that's likely to actually have some effect."
Council coastal scientist Oliver Wade said there was "work in the pipeline" to resolve sediment coming off the catchments.
"There's no quick answer to resolve it, the best thing we can do is to stop that sediment coming from the land so the estuary can regenerate itself."