Capturing dissolved organic carbon dynamics with Landsat-8 and Sentinel-2 in tidally influenced wetland–estuarine systems

Estuarine and coastal wetlands are among the most productive, ecologically valuable, and economically important ecosystems on Earth. Through tidal inundation and lateral export, estuarine marshes 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. Here, for the first time, we merged high resolution data from the constellation of Landsat-8/Operational Land Imager (OLI) and Sentinel-2A/B MultiSpectral Instruments (MSI) to examine dissolved organic carbon (DOC) dynamics in a tidally influenced marsh–estuarine system. Often referred to as the “Everglades of the North”, the Blackwater National Wildlife Refuge is the largest marsh system in the Chesapeake Bay and one of the most ecologically important areas in the United States. A multiple linear regression approach linking DOC to the spectral shape of water remote sensing reflectance was used to capture marsh DOC export and examine spatial features and temporal changes in DOC over a broad range of conditions (DOC in the range of 2.32–19.9 mg/L), across multiple years, different seasons, and tidal regimes, with a relative error (mean average percent difference) of 23%. Data consistency between satellite sensors was evaluated, followed by the generation of a long term, multi-sensor DOC data record that provided more frequent observations. Combining data from the three satellites revealed the strong impact of marsh outwelling at the larger ecosystem scale, its seasonal variability, and the importance of other environmental factors, including wind conditions, river discharge, and extreme weather events, in shaping DOC dynamics along complex, tidally influenced terrestrial–aquatic interfaces.