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Turning the tide on acid runoff

Scientist dips hand in black water.

Restoring the condition of coastal floodplains is pivotal to restoring the health of estuaries.

That was the key message shared by attendees at a recent field trip of drained wetland sites of the Macleay Valley.

The group shared insights of what happens when wetlands are drained and ways to best rehabilitate these areas.

NSW DPI Fisheries Manager Max Osborne, one of the organisers, said the day highlighted the importance of restoring coastal wetlands.

“When our coastal floodplain wetlands are under stress the whole estuary suffers. In the Macleay River estuary, historic drainage of wetlands has impacted water quality and the ecosystem as a whole,” he said.

“Many of these waterways and backswamps were drained by 1970. This resulted in the exposure of acid sulphate soils which has led to acidified and scalded soils, and acidic waters entering our rivers. These acidic waters harm aquatic life, cause fish diseases such as Red Spot and even dissolve the shells on shellfish such as oysters.”

He said not only has floodplain wetland drainage caused sulphuric acid runoff, it has also increased the frequency and extent of low oxygen blackwater events.

“In drained floodplain wetland areas, native flood tolerant wetland plants have been replaced with grasses that are often killed when inundated. This can occur even after small rainfall events, not just floods."

“When these grasses die, they rot, using up the oxygen in the water. This results in water high in organic matter and low in oxygen (often called blackwater) entering our creeks and rivers."

“Blackwater can devastate aquatic life in our rivers and creeks. Restoring wetlands is one step towards reducing the frequency of these harmful events,” he said.

Mr Osborne said we can turn the tide on acid sulphate soils and blackwater events.

“Across coastal NSW, we are working with key agencies, private landholders and experts in hydrology to restore tidal flows to drained wetland areas. Restoring tidal flows to these acid sulphate affected areas will bind up the acid in the soils, reverting generally non-productive paddocks back to coastal wetland ecosystems. We can also revert manipulated areas to natural draining of freshwater - to slow the generation of more acid."

"At the Clybucca Wetlands, near South West Rocks on the Mid Coast of NSW, we are conducting on ground works on government-owned sections of land that will reinstate a more natural draining of the wetland."

“The current stage of the Clybucca Wetlands rehabilitation project will reduce the amount of acid leaving the areas and entering our coastal creeks and estuaries over time, without impacting neighbouring grazing properties,” he said.

Attending the coastal floodplain field day were staff involved in managing coastal wetlands from DPI Fisheries, North Coast Local Land Services, Kempsey Shire Council, Tweed Shire Council, Environment and Heritage Group, Soil Conservation Service, and the University of NSW.

The Clybucca Wetlands rehabilitation project is being undertaken by Transport for NSW, North Coast Local Land Services in partnership with DPI Fisheries and funded under the Recreational Fishing Trust Flagship Fisheries Grant and the NSW Marine Estate Management Strategy. On ground works will be conducted by NSW Soil Conservation Service.

To find out more about the Coastal Floodplain Wetland rehabilitation project funded under the NSW Marine Estate Management Strategy go to: Coastal wetland rehabilitation (nsw.gov.au)

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