Mangrove Rehabilitation to Improve Coastal Resilience: Lessons fromthe Blue Heart Wetlands, Sunshine Coast, Queensland, Australia

Efforts to restore and rehabilitate mangroves have gained global recognition in climate change mitigation programmes, mainly because of the ability of these ecosystems to store atmospheric carbon long-term while keeping pace with sea-level rise. The Blue Heart project was initiated by Sunshine Coast Council, Queensland, Australia to rehabilitate degraded agricultural land on the low-lying (<1 m Australian Height Datum) Maroochy River floodplains in Queensland, Australia, back to coastal wetlands. In order to monitor surface elevational changes, subsidence and sedimentation rates in the Blue Heart area, a network of 24 Rod Surface Elevation Table Marker Horizon (RSETMH) stations has been deployed across two rehabilitating sites (Phase 1 and Phase 2) based on elevation (high: >0.5 m; medium: 0.25-0.7 m; and low: <0.25 m) and two mature mangrove forests (reference sites 1 and 2). In addition, the soil carbon stocks of wetlands undergoing rehabilitation and mature mangroves were quantified following the loss on ignition workflow. The preliminary data indicate that surface elevational changes in Blue Heart wetlands range from -8.68 (mature mangroves in reference site 2) to 16.32 mmyear-1 (immature mangroves in Phase 1). The average elevational change for rehabilitating site in Phase 1 is 13 mmyear-1 , which surpasses the rate of local sea-level rise of 2.1 mmyear-1 from 1987 to 2021. The soil carbon stock estimates for mature mangrove forests (41 kgm-3 ) are comparable to those for other sub-tropical mangrove wetlands in Australia, and higher than those for Phase 1 (19-27 kgm-3 ) and Phase 2 (8.4-12.7 kgm-3 ) rehabilitating wetlands in the Blue Heart area. In summary, these results indicate that wetland rehabilitation in the Blue Heart area will keep pace with current sea-level rise by elevating the land surface and increasing the soil carbon stocks.