Mark Gall (left) and NIWA colleagues preparing to launch an estuarine monitoring buoy from the NIWA survey vessel Rangitahi III (image: L. Thompson)
NIWA says sedimentation in many New Zealand estuaries has increased 10-fold over the last 150 years, representing a loss for both land and estuary productivity.
And fine sediment entering the Kaipara Harbour, north of Auckland, is having a detrimental effect on the harbour’s overall health.
Last year high concentrations of sediment flowing into the Southern Kaipara Harbour contributed to it receiving a D for water quality from the Auckland Council – one of the worst grades in the Auckland region.
The Kaipara, one of the largest estuaries in the Southern Hemisphere, holds one of the last significant seagrass meadows on the west coast. The meadows provide a key nursery ground for juvenile fish species such as snapper, trevally and mullet.
But NIWA coastal scientist Andrew Swales, says increasing amounts of fine sedimentation running into the harbour is preventing light from reaching the meadows, in turn reducing feeding opportunities for fish, shellfish and birds.
However, a united effort to try and work out where the main sources of sediment are coming from and what can be done to reduce them is now underway.
Researchers from NIWA, Auckland Council and the Northland Regional Council are establishing three Estuarine Monitoring Systems to help keep track of sediment and pollutants.
The stations will be based at Tikonui Wharf near Ruawai, and further south in the tidal reach of the Hoteo River and at Orongo Point.
Their main focus will be to measure water quality in the harbour and tidal creek areas, in particular water clarity which is affected by fine sediment.
The first station (left) was launched by NIWA researchers in the Hoteo River in May and is powered by solar panels.
It will take continuous measurements of water salinity, temperature, turbidity, as well as weather conditions and tidal currents and will feed back the data remotely to scientists in real-time.
“Part of this work we’re also interested in microbes”, says Andrew Swales. “Fine sediments actually act as a carrier for a whole raft of other contaminants like microbes, heavy metal compounds, run off from roads. Fine sediments are the thing that links a lot of those contaminants to the estuary…that’s why they’re such a problem.”
Another of the team’s researchers, Mark Gall, says the project will provide the opportunity to collect information from the field via high temporal and spatial detail.
“We need to know the different components that make up the colour of the water, so that we can tease those apart and develop relationships with light attenuation in the water.”
The project, funded by local and central government, will provide information for at least two years, and will be made publically available via Auckland Council’s website.
“I think there’s a general feeling the Kaipara’s been the forgotten harbour in this part of the country,” says Andrew Swales. “Until a few years ago it wasn’t getting a lot of attention in this way…this is a really concerted effort now to better understand what’s driving the ecology and environmental quality of the harbour.”