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Variable Responses of Coastline Dynamics Controlled by Migrating Subtidal Mudbanks
  • Job de Vries,
  • Barend van Maanen,
  • Steven de Jong
Job de Vries
Universiteit Utrecht,Utrecht University

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Barend van Maanen
University of Exeter
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Steven de Jong
Utrecht University
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Coastal wetlands provide a livelihood for local communities and simultaneously provide services that include coastal protection, enhanced carbon storage and habitats provision for both terrestrial- and marine life. Yet, the development of climate resilient management strategies that need to account for changes that might occur in the coming decades is challenging due to the variable response of coastal ecosystems. This is because coastal ecosystems, including mangroves, wetlands and tidal flats, are directly linked to coastline dynamics, as coastlines can move seaward, when waves are low and sediment availability is high, or retreat when the opposite is true. Particularly the long-term fate of the mud dominated coastline of Suriname, part of the Guianas coastal system stretching from the Amazon to the Orinoco delta, is determined by migrating subtidal mudbanks that cause a cyclic instability of alternating erosion and progradation phases. We present a semi-automatic remote sensing approach to quantify the influence of mudbank migration on coastline dynamics along the entire coast of Suriname. We validated our approach with high resolution drone imagery collected at contrasting locations, indicating average accuracy of changes in coastline position to be within 50 meters. This suggest we can apply our methodology on all available Landsat images between 1985 and 2020, acquired over the heterogonous and complex coastal landscapes. The results show that regional forcing mechanisms, related to migration of six to eight subtidal mudbanks in front of the Suriname coast, have a strong imprint on local coastline dynamics with an average 25 m/yr-1 expansion during mudbank presence, and 8 m/yr-1 retreat of the coastline during mudbank absence between 1986 and 2020. More importantly, we found that not all spatial and temporal variations in the magnitude and timing of local changes can be explained by migrating mudbanks. This demonstrates the importance of incorporating changes that cannot be explained by regional forcing mechanisms in management frameworks that aim at explaining current variability and predicting future coastline changes.