Investigating the contributions of herbaceous vegetation biomass to soil accretion in Louisiana's coastal deltaic wetlands using airborne imaging spectroscopy

Understanding the relationship between vegetation productivity and soil accretion is critical for assessing the resilience of deltaic wetlands to relative sea-level rise. This study integrates airborne imaging spectroscopy from NASA's AVIRIS-NG sensor with field measurements from the Delta-X campaign to quantify herbaceous vegetation contributions to vertical accretion processes in the Mississippi River Delta's coastal wetlands. We developed imaging spectroscopy–based products for live above- and belowground carbon (AGC, BGC), and aboveground necromass (AGN; or non-photosynthetic vegetation), the latter being derived using a novel combination of spectral unmixing and Random Forest regression. These vegetation maps were evaluated alongside in situ soil accretion measurements—including surface sediment accretion, soil bulk density, organic matter content, and soil organic carbon density—derived from feldspar marker horizons. These data were sampled concurrently with airborne campaigns conducted in April and August 2021 to coincide with the early- and peak-biomass season conditions. While vegetation metrics explained a limited fraction of variability in total vertical accretion, AGC, AGN, and BGC together accounted for a substantial portion of the variance in soil bulk density and organic carbon density, indicating that vegetation-driven organic matter inputs exert a stronger control on soil mass and carbon storage than on short-term elevation gain. These results demonstrate that airborne imaging spectroscopy can resolve distinct vegetation pools that differentially influence wetland soil properties, providing new insight into the coupled vegetation–soil processes underpinning blue carbon dynamics. This highlights imaging spectroscopy's value for advancing landscape-scale assessments of wetland resilience and informing management strategies in sediment-deprived coastal basins. • Above- and belowground wetland carbon stocks were mapped in coastal Louisiana. • Spectral unmixing enabled mapping of non-photosynthetic vegetation (or necromass). • Imaging spectroscopy captured seasonal shifts in biomass–necromass distributions. • Biomass patterns explained variance in soil organic carbon density and bulk density. • Imaging spectroscopy enables regional-scale assessment of wetland accretion drivers.