ESTIMATION OF TIDAL MARSH BLUE CARBON STORAGE USING A LIDAR AND OPTICAL REMOTE SENSING BASED MODEL

Tidal marshes serve as important sinks and sources for nutrients, sediments, and “blue carbon.” Blue carbon ecosystems such as tidal marshes accrete large amounts of carbon with limited area and protect coastlines from increasing impacts of climate change. Much attention has been dedicated to the quantification of sedimentation rates in tidal marshes, however estimation of carbon storage in marsh peat is less understood. Driven by tidal inundation, surface topography, and sediment supply, soil organic carbon (SOC) in marshes varies spatially with several parameters, including marsh platform elevation, proximity to the marsh edge and tidal creek network, and vegetation percent cover and structure. We applied lidar and optical remote sensing to extract topographic, suspended sediment supply, water inundation, and vegetation parameters from tidal marshes to map SOC at the meter scale.

In June and July 2021, fixed volume soil samples were collected at four northeast tidal marshes with distinctive morphologies to aid in building our predictive models. Tidal creek networks were delineated from 1-m resolution topo-bathy lidar data using a semi-automated workflow in GIS. Sample distance to tidal creeks and flow distance to the marsh edge were then determined. Vegetation and water indices were derived from 2-m WorldView satellite imagery for all sites. Non-linear multivariate regression models were developed to predict soil organic content, bulk density, and carbon density as a function of these predictive metrics at each site and across sites. Results show the topographic parameters perform well at sites with a single connected creek network. Generally, SOC increases with increasing distance from tidal creeks and the marsh edge. Addition of remote sensing parameters results in adjusted-R² values ranging from 0.67 to 0.72, which outperforms the topographic models and allows for cross-site modeling with greater accuracy. The normalized difference water index (NDWI) is a good indicator of tidal inundation across a marsh and annual particulate organic carbon (POC) appears to represent sediment supply which is a major control of SOC variability across marsh sites. This method will be applied to additional Northeast saltmarsh sites to validate and better understand the predictive power of our models at a regional scale.