High-Resolution mapping of biomass and distribution of marsh and forested wetlands in southeastern coastal Louisiana

This study estimates herbaceous and forested wetland coverage and aboveground biomass (AGB) within the Atchafalaya and Terrebonne coastal basins representing sediment rich and sediment poor coastal regions of southern Louisiana. Louisiana coastal wetlands account for approximately one third (37%) of the estuarine wetland area in the conterminous United States, yet the spatial distribution of their extent and aboveground biomass estimates are not well defined. Despite the importance of Louisiana’s coastal wetlands, existing maps on their extent are often outdated yet repeatedly used in national greenhouse gas (GHG) inventories and within regional aboveground biomass and carbon content estimates. Sentinel-2 optical satellite data was used within an object-oriented machine learning approach to classify wetland extent, mapping the spatial distribution of the coastal wetlands at high-resolution. A total wetland extent of 2950 km2 was mapped during a period of peak biomass in September 2017, comprised of forested and herbaceous wetlands (accuracy >90%) and demonstrated considerable differences (793.7 km2) from currently available estimates of wetland area. The distribution of aboveground biomass (AGB) was mapped using class averaged values derived from field data collected during May and September 2015. Total herbaceous biomass at the study site increased by 108.9% from May (668,684.5 Mg) to September (1,396,969.2 Mg) whilst the total woody vegetation biomass (27,667,232.1 Mg) was sampled in May only. This method provides a tractable means of mapping wetland extent and biomass, in a region threatened with wetland loss under projections of increasing sea-level rise and local subsidence.