A Brief History of Delta Formation and Deterioration

Abstract

The Mississippi River (MR) delta formed over the last several 1000 years as a series of overlapping deltaic lobes in various stages of progradation and deterioration that were sustained by overbank flooding and crevasses of the Mississippi River and active distributaries. To the west of the delta complex stretches the smooth shoreline of the Chenier Plain, which was created by the intermittent westward drift of sediments from the MR forming a series of beach ridges and mud flats. Beginning in the eighteenth century and greatly accelerating throughout the twentieth century, the delta has been impacted by a variety of human activities, most importantly by the separation of the Mississippi River from its deltaic plain, which has caused massive wetland loss during the last century. Other factors exacerbating wetland loss includes altered hydrology due to the proliferation of dredged canals and deep-well fluid withdrawal associated with the oil and gas industry, intentional impoundment for waterfowl management, and herbivory by nutria. The only place where wetland loss has not been high is at the Atchafalaya and Wax Lake delta complex, which are part of the beginning stages of a major new deltaic lobe development fed by the Atchafalaya River distributary that carries about a third of the combined lower MR discharge. One of the greatest threats to MR delta wetlands is accelerating sea-level rise due to a combination of subsidence and eustatic sea-level rise (ESLR), which ranges from 2–17 mm year−1 in the delta.