Why is the BTES losing land?
The most important factor contributing to land loss in the BTES is subsidence, a complex process in which marsh sediments compact and sink under their own weight. Historically, annual floods over the banks of the Mississippi River provided freshwater and sediment inputs to BTES marshes and kept them above water. Levees were constructed to protect communities across the nation from these floods, but they also prevent water and sediment from reaching the BTES marshes.
Subsidence drowns coastal marshes, causing chemical changes in wetland soils which eventually kill marsh vegetation. Without plant roots to hold it together, marsh soil breaks up and is carried away by wave action. The end result is that marsh is converted to open water. This additional volume of water causes an increase in the tidal prism, forcing passes to enlarge and reducing the lengths of barrier islands, which protects interior marshes from wave action and hurricanes. Barrier islands are also subsiding, and due to both these stressors, ultimately disappear without new sediment inputs.
Other human-caused and natural factors can influence land loss rates in the BTES. For example, canals and raised roadbeds, breached natural ridges, and other hydrologic modifications can interrupt tidal exchange and allow salt water intrusion.