After 18 months of tidal reconnection, it is getting green inside the salt pond under investigation by the ‘Salt to C’ research team from the Goyder Institute for Water Research. Tidal re-connection is a top priority activity recommended by a national blue carbon working group for establishing a methodology under the Emissions Reduction Fund for blue carbon. Blue carbon is the term used to describe carbon captured by ocean and coastal ecosystems.
The Salt to C project is of nation-wide interest as a proof of concept for blue carbon benefits from tidal re-connection and salt field restoration. This interdisciplinary project, led by Professor Sabine Dittmann from Flinders University, involves scientists from Flinders University, the University of Adelaide, the University of South Australia, the Department for Environment and Water, as well the Australian National University and Silvestrum Climate Associates.
The scientists in the Salt to C project have investigated changes in the carbon stocks in sediments and vegetation and greenhouse gas fluxes, within the pond and adjacent reference areas. There has been a net gain of organic carbon in the sediment surface layers, mostly likely through seagrass (wrack) accumulating in the pond. While long-term sediment accumulation rates were highly variable in and outside of the pond, surface elevation tables are indicating recent sediment deposition since reconnection. The flux of greenhouse gases also varied by elevation, with emissions at higher elevation and uptake of CO2 in lower lying areas with moister sediments. The comparison between the trial pond and reference area indicates that further restoration of vegetation within the pond can reduce emissions.
Based on the elevation and predicted vegetation changes, most of the pond can be recolonised by mangrove. Measurements from adjacent mangrove forests have yielded an average above ground biomass of 240 t dry mass per ha, equivalent to 413 tCO2e per ha. The biomass estimate is higher than reported for other temperate mangroves and could indicate the potential for carbon benefits through restoration of mangrove forests.
Saltmarsh plants have been the fastest colonisers in the pond and their arrival was subject to seasonal differences in seed dispersal, which was detected with monthly deployment of seed traps. On a very positive note, the saltmarsh plants now established within the pond are flowering and setting seed, which can accelerate further recolonisation.
The salt pond in November 2017 (left) and December 2018 (right) after tidal reconnection.
The project has also been working on assessing co-benefits of reconnection, through a survey of social values and cultural services, as well as other ecosystem services using global and local data. Findings from the project have been presented at national conferences and at workshops for state and federal environment departments to develop blue carbon strategies and accounting through advancing methodologies of the Emissions Reduction Fund, or testing accounting approaches for voluntary carbon markets. Outcomes from the Salt to C project will be of strategic importance to South Australia and Australia for further developments in the topical area of blue carbon.
Contact Professor Sabine Dittmann for more information about the Salt to C project.