Capturing biogeochemical exchanges in tidally influenced wetland-estuarine ecosystems using high spatial resolution Landsat-8 and Sentinel-2 imagery

Abstract:

At the intersection of terrestrial and aquatic landscapes, coastal wetlands are biogeochemical and ecological hot spots, playing important roles in shoreline protection, carbon sequestration, sediment regulation, coastal biodiversity and fisheries production. Through tidal inundation and lateral export, coastal wetlands also exert a strong influence on the amount and quality of carbon and nutrients exchanged between the land and the ocean. Yet, current understanding of the role of these "blue carbon" ecosystems on estuarine optics, biogeochemistry, and ecology is largely based on limited field observations at point locations, due to the coarse resolution of existing and heritage satellite ocean color sensors. Data fusion from high spatial resolution instruments, on constellations of polar-orbiting and, soon, geostationary satellites, offers a unique opportunity to detect the strong spatial heterogeneity that characterizes wetland-estuarine interfaces at a global scale. Here, we merged high resolution data from the constellation of Sentinel-2A/B and Landsat-8 satellites to examine dissolved organic matter (DOC) dynamics in the estuarine waters adjacent to the Blackwater National Wildlife Refuge, the largest marsh system in the Chesapeake Bay. Often referred to as the "Everglades of the North", this wetland is one of the most ecologically important areas in the state of Maryland. A multiple linear regression approach, linking DOC to the spectral shape of water remote sensing reflectance, was used to capture spatial features and temporal changes in DOC over a broad range of conditions (~2-20 mg/L) across multiple years, different seasons, and tidal regimes. Combining data from the three satellites, revealed the strong impact of marsh outwelling, its seasonal variability, and the importance of environmental factors, including wind conditions, precipitation, and extreme weather events in shaping DOC dynamics along highly vulnerable wetland-estuarine interfaces.