Good example of former flooded wetland areas subsiding through the draining of the area--6 feet of vertical elevation loss, 1924-2009. A good way to show what happens to exposed organic soils when these (former) wetland soils are drained and exposed to the open atmosphere.
The last time period rate of elevation loss may be due to the fact the soil has been pretty compacted in the decades before and a lot of the organic material has been oxidized and lost. It would be good to see what the composition of the remaining soil.
This is seen across wide areas of coastal Louisiana and the northern Gulf. This loss of soil organic material, the compaction and other subsidence effects and the rise of sea levels- all making a relative sea level rise rate about 4 times greater than a coastal area like Pensacola.
The big issue now is to see this occurring at a very rapid rate in Carbon emission/loss of the northern tundra through melting and fires. The release of carbon (CO2) into the atmosphere from this can be very large.