Wetlands Australia 32: Tidal reconnection of salt fields benefits biodiversity and carbon capture

Authors: Sabine Dittmann (College of Science & Engineering, Flinders University), Luke Mosley (University of Adelaide), Jason Quinn (Department for Environment and Water), Kieren Beaumont (College of Science & Engineering, Flinders University), Beverley Clarke (College of Humanities, Arts & Social Services, Flinders University), Michelle Clanahan (College of Science & Engineering, Flinders University), Courtney Cummings (Environment Protection Authority, South Australia) & Tony Flaherty (Adelaide & Mount Lofty Ranges Natural Resources Management Board)

Restoration of tidal wetlands can play an important part in future-proofing coastlines to mitigate climate change effects. Reintroducing tidal flow to ponded areas is a possible restoration activity which we trialled through installing a tidal gate at a salt pond. The trial demonstrated that restoring the salt field to a living shoreline of tidal wetlands would be a ‘triple win’ for climate mitigation (carbon sequestration), adaptation (as a nature-based defence against sea level rise) and biodiversity conservation.

Tidal wetlands provide multiple ecosystem functions and services, which are lost when habitats are destroyed. Can restoration reverse this loss? The cessation of salt production at the Dry Creek salt field north of Adelaide provided the opportunity to investigate whether tidal reconnection can remediate salt ponds, re-establish saltmarsh, mangrove and shorebird habitat, and be a pathway towards realising blue carbon opportunities for South Australia.

We trialled reintroducing tidal flow to a previous salt pond and documented rapid revegetation through natural seed dispersal. The pioneer saltmarsh species Suaeda australis and Sarcocornia quinqueflora grew quickly to mature stages inside the trial pond. Recolonization by macroinvertebrates and shorebirds followed. We measured elevated soil carbon concentrations as well as carbon stored in the emerging vegetation. Based on our survey of cultural ecosystem values it further emerged that human well-being can be enhanced when salt fields are restored to natural tidal wetland ecosystems.

Left: Salt pond shortly after reconnection. Right: Nearly two years later. Photo: Sabine Dittmann

We modelled the carbon capture over time and hypothetical tidal reconnection of further salt ponds, also guided by our data from a nearby site where we analysed the carbon stored in mangrove trees and soils of known age over an 80 year colonisation sequence. The model showed that carbon sequestration increases with the size of the restored area. For example, the estimated increase in carbon stocks from potentially reconnecting over 1200 hectares of low-lying ponds could exceed 400,000 tonnes CO₂ equivalent within 30 years. Given sea level rise, landward retreat options become important to maintain the ecosystem functions and services of tidal wetlands over longer time frames.

The project provided a proof of concept that opening a salt pond to tidal flow can lead to restoration of coastal wetland without adverse effects. Introducing tidal flow to a salt pond is a feasible activity, which generates benefits for biodiversity and carbon offsets. The tidal trial at Dry Creek has become an important pilot project for advancing blue carbon in Australia.

Saltmarsh vegetation emerging in the reconnected salt pond. Photo: Kieren Beaumont

Further Information

• From salt to C; carbon sequestration through ecological restoration at the Dry Creek Salt Field
• Proof of concept for tidal re-connection as a blue carbon offset project
• Samphire Coast Icon Project
• Shorebird population monitoring in Gulf St Vincent: 2016-17 Annual report
• Video on the tidal reconnection: Restoring the Dry Creek Salt Field in South Australia
• South Australian Department for Environment and Water: Climate Change Strategy and Blue Carbon Strategy