Mapping Blue Carbon Ecosystems from Earth Observations at National Scale for Papua New Guinea

Christopher J Owers^1*Richard M Lucas²Carole Planque³Daniel Clewley⁴Matt Paget⁵Chloe Fitzpatrick¹Annette Burke¹Freddie Alei⁶Mitchell Lyons⁷Andrew D.L. Steven⁸

• ¹Earth Sciences, School of Environmental and Life Sciences, The University of Newcastle - Callaghan Campus, Callaghan, Australia
• ²Department of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, United Kingdom
• ³EnviroSPACE Laboratory, Institute for Environmental Sciences, Universite de Geneve, Geneva, Switzerland
• ⁴Environmental Intelligence Group, Plymouth Marine Laboratory, Plymouth, United Kingdom
• ⁵CSIRO Environment, Commonwealth Scientific and Industrial Research Organisation, Canberra, Australia
• ⁶Environmental Science and Geography Division, University of Papua New Guinea, Waigani, Papua New Guinea
• ⁷University of New South Wales, Sydney, Australia
• ⁸CSIRO Environment, CSIRO Queensland Biosciences Precinct, Saint Lucia, Australia

National maps are essential to support the conservation, restoration, and sustainable management of Blue Carbon Ecosystems (BCE). This is particularly important for nations in the the Indo-Pacific region, including Papua New Guinea (PNG), that aspire to integrate these ecosystems into their nationally determined contributions (NDCs) for ecosystem accounting. This study focussed on mapping the extent of BCEs in PNG using Earth observation data for the year 2020 and reporting on biomass and carbon storage services. Land cover categories were generated using the Living Earth framework for the 15 coastal provinces of PNG. Total BCE area in PNG (14,353 km²) comprised of 30% mangrove, 65% lowland peat swamp forest, 3% saltmarsh and 2% seagrass. Lowland peat swamp forests contributing the greatest biomass (137.94 ± 67.10 Tg) followed by mangroves (71.79  27.16 Tg), with a total biomass of 212.99 ± 95.89 Tg. Across PNG a total of 710.46 ± 362.75 Tg C were estimated for below-ground carbon of BCEs (reporting to 1 m depth), almost 7 times more than above ground carbon (102.14 ± 45.97 Tg C). This study highlights the need for a consistent and standardised framework for mapping BCEs, which can support coordinated management of coastal landscapes across provinces that contribute to national policies and NDC reporting. This case study can be used as a demonstration for other nations where similar opportunities and challenges may exist for mapping BCE using Earth observations, with a framework that can be compared and adapted to user requirements.