Researchers target muddy Kaipara Harbour

Reducing the amount of silt getting into the Kaipara Harbour is one of the concerns being tackled by a joint initiative between the National Institute of Water and Atmospheric Research, Northland Regional Council and Auckland Council.

Sediment deposited on the seabed can smother marine life, influence the distribution and extent of habitats such as mangroves, seagrass beds and salt marshes. It infills estuaries and causes a shift from sand to mud-dominated environments.

Suspended sediment causes turbidity (muddiness) which restricts light transmission to aquatic plants, like seaweeds and seagrass, which require photosynthesis for growth. It affects the ability of fish and birds to see and eat food - clogging fish gills and the feeding structures of shellfish.

The research will provide valuable data to enable informed decision-making on activities and land management which impact on these ecosystems. The intention of the collaborative group is to move towards a "limits based approach" in the areas where contamination enters the harbour.

New monitoring stations which measure suspended sediment and water clarity have already been installed on three of the northern Kaipara Harbour 's tributaries - the Northern Wairoa, Mangakahia, and Maunganui Rivers.

Permanent continuous monitoring equipment is being installed on the Tikinui wharf on Kaipara's Pouto Peninsula which will provide minute-by-minute information on temperature, salinity and turbidity, sea state (waves) and weather, said Richard Griffiths, marine research specialist for NRC.

Similar initiative are taking place elsewhere in the Kaipara.

The Kaipara Harbour is a significant social, cultural and economic resource. It is a major nursery for juvenile fish species such as snapper and trevally - its vast seagrass meadows support a wide variety of other marine organisms, shellfish and birdlife, including the critically endangered tern.

Deforestation, agriculture, forestry and urban development have dramatically increased sediment loads being dumped into the harbour from the catchment areas of its main river systems. By far the greatest culprit is the Northern Wairoa, which contributes up to 63 per cent of the harbour's total catchment area.

The two councils plus the Kaipara District Council all have roles in the management of the harbour, making collaboration with Niwa a good opportunity to share expertise, resources and valuable research dollars. They are also working in collaboration with the iwi-led Integrated Kaipara Harbour Management Group.

The Kaipara Harbour is one of the biggest in the world and the second largest in the southern hemisphere. It is 60 kilometres long and at high tide covers 947 square kilometres. The harbour shoreline is about 800km long, and is the drainage catchment for about 640,000ha of land, much of which is in Northland.