Estimating Relative Sea-Level Rise and Submergence Potential at a Coastal Wetland
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A tide gauge records a combined signal of the vertical change (positive or negative) in the level of both the sea and the land to which the gauge is affixed; or relative sea-level change, which is typically referred to as relative sea-level rise (RSLR). Complicating this situation, coastal wetlands exhibit dynamic surface elevation change (both positive and negative), as revealed by surface elevation table (SET) measurements, that is not recorded at tide gauges. Because the usefulness of RSLR is in the ability to tie the change in sea level to the local topography, it is important that RSLR be calculated at a wetland that reflects these local dynamic surface elevation changes in order to better estimate wetland submergence potential. A rationale is described for calculating wetland RSLR (RSLRwet) by subtracting the SET wetland elevation change from the tide gauge RSLR. The calculation is possible because the SET and tide gauge independently measure vertical land motion in different portions of the substrate. For 89 wetlands where RSLRwet was evaluated, wetland elevation change differed significantly from zero for 80 % of them, indicating that RSLRwet at these wetlands differed from the local tide gauge RSLR. When compared to tide gauge RSLR, about 39 % of wetlands experienced an elevation rate surplus and 58 % an elevation rate deficit (i.e., sea level becoming lower and higher, respectively, relative to the wetland surface). These proportions were consistent across saltmarsh, mangrove, and freshwater wetland types. Comparison of wetland elevation change and RSLR is confounded by high levels of temporal and spatial variability, and would be improved by co-locating tide gauge and SET stations near each other and obtaining long-term records for both.
KeywordsRelative sea-level rise Wetland elevation Tide gauge SET Vertical accretion Shallow subsidence Shallow expansion
K. Boone and J. Lynch drafted Fig. 1, and J. Lynch drafted Fig. 2. I am deeply indebted to the following individuals for providing critical reviews of earlier draft versions of this manuscript: S. Gill, P. Hensel, B. Horton, J. Lynch, K. Krauss, K. McKee, two anonymous reviewers, and C. Currin. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government. This research was funded by the U.S. Geological Survey Climate and Land Use Research & Development program.
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