A preliminary estimate of the contribution of coastal blue carbon to climate change mitigation in New Zealand

ABSTRACTThe scale at which New Zealand is currently storing and sequestering blue carbon, and could create additional blue carbon via restoration, has been unclear. Here, we calculate a preliminary estimate for the current extent of three key blue carbon ecosystems (saltmarshes, mangrove forests and seagrass meadows), their carbon stocks and their carbon sequestration rates using the best available data to provide a preliminary estimate of blue carbon in New Zealand. We also use local examples to explore opportunities to create additional blue carbon. Based on the available literature, we estimate the current extent of New Zealand’s blue carbon ecosystems to be 76,152 ha, which is 1.0% of the area of terrestrial native forests. Our preliminary estimate of New Zealand’s blue carbon stock is 2.66–3.76 Mt of carbon, with a current carbon sequestration rate of 0.12 (0.05–0.26) Mt/CO2/yr, which is equivalent to 0.16% of New Zealand’s 2021 gross emissions. Restoration of saltmarshes could enhance their carbon sink capacity, mangrove forests are naturally expanding and seagrass meadow restoration techniques at scale are still in development. Developing a national framework for blue carbon protection, monitoring and restoration is important as part of New Zealand’s climate change mitigation and adaptation efforts.KEYWORDS: Climate changeblue carbonsaltmarshseagrassmangroverestorationconservationcarbon sequestrationtidal marshNew Zealand AcknowledgementsThis project was supported by Deakin University and Sea Green Pte Ltd. PIM thanks the support of an Australian Research Council Discovery Project (DP200100575). AB and DEC thank support from the Cawthron Institute. RB acknowledges support from MBIE Smart Idea project (Carbon sequestration via New Zealand’s estuarine environments: Implications for greenhouse gas budgets – C01X2109). OA acknowledges the support from MBIE, GNS Science and the Antarctic Research Centre, Victoria University of Wellington. We would also like to acknowledge Micheli Costa for assistance with Figure 1 and Helen Kettles for helping retrieve data.Author contributionsThe idea for the manuscript was conceived by FR who organised and directed the writing of the manuscript. All other authors contributed to the writing and editing of the manuscript.Competing financial interestsFR works for Carbonz (New Zealand business number: 9429049537871). Carbonz trades voluntary carbon credits in New Zealand however is currently not trading blue carbon credits. The other authors declare no competing financial interests.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported by Deakin University; Sea Green Pte Ltd.; Cawthron Institute; Australian Research Council Discovery Project [grant number DP200100575]; MBIE Smart Idea Project [grant number C01X2109]; MBIE through the Global Change through Time Programme (Strategic Science Investment Fund, contract C05X1702); NZ SeaRise Programme funded by MBIE to the Research Trust at Victoria University of Wellington (Contract ID - RTVU1705).