New data suggests Louisiana coast is sinking at an accelerated rate

A new subsidence map for coastal Louisiana
Jaap H. Nienhuis, Torbjörn E. Törnqvist, Krista L. Jankowski, Anjali M. Fernandes, and Molly E. Keogh

Data: Data for this study was collected by another study (with a lot of the same authors) by Jankowski et al. (2017). The data is small-scale changes in wetland surface elevation – this simply means how high or low the wetland is compared to the water table.

Methods: These authors used a new technique through the Coastwide Reference Monitoring System (CRMS) program. They used long steel rods called surface-elevation-marker horizon records – in this case these rods had been in place for 6-10 years and allows the scientists to calculate how quickly the coastline is sinking (sinking of land is called subsidence). This working group also used GPS time series (data from GPS collected over a period of time) of stations below the land surface to capture deeper sinking.

Results: Their results are clearly visualized in the map of the coastline. The results indicate that there is a widespread area of subsidence (sinking) recorded at the land surface and that the rate of sinking is relatively uniform across coastal Louisiana. The results presented in this study are considerably higher than in other recent studies that have used other methods.

This subsidence map for the coastal Louisiana area is based on observational data (all of the black dots) for the last 6-10 years. The areas that are in white or gray were excluded from the analysis. These areas are either cities or agricultural areas, which have modified drainage systems (such as underground sewer systems). The warmer colors indicate increased rates of subsidence. 

Why is this study important? The gulf coast has experienced substantial wetland loss. These low-elevation coastal zones (LECZs) are very sensitive regions considering the recent rises in sea level, which are driven by the increasing climate change. In order to understand the acceleration of wetland loss, it is important to understand what has happened in the recent past. Scientists can then use this data to predict the migration of the coastline and help prevent damage and loss of life.

The big picture: These new techniques for exploring data in low-elevation coastal zones can now be applied to other locations in the world. With more scientists exploring changing coastlines, there will be a greater understanding on how sea-level rise will affect humanity in the near future.

Citation: Nienhuis, H. J., Törnqvist, T.E., Jankowski, K.L., Fernades, A.M., and Keogh, M.E. A new subsidence map for coastal Louisiana. GSA Today, vol. 27. DOI: 10.1130/GSATG337GW.1

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