Deltas in Crisis

Deltas in Crisis

During the last decade, a substantial amount of concern has arisen regarding the health of the planet's major deltas. Over-exploitation of deltaic resources by humans, the introduction of pollutants, and excess nutrients to the rivers, as well as the management of river water that feeds deltas has severely damaged the sensitive environments of many deltas. Additionally, reduced sediment loads in many deltas, because of the construction of dams, coupled with global sea level rise and/or local land subsidence has resulted in widespread loss of deltaic wetlands and fronting sandy barrier shorelines. Because deltaic plains are so heavily relied upon by humans and, in some cases, are densely inhabited by humans, there are, for some deltas, widespread efforts to try to halt coastal erosion and environmental damage.

For example, the wetlands of the Mississippi River delta have undergone substantial change during the last century, with large areas of wetlands converted to open water because of relative sea level rise and erosion by storms. The rate is just staggering, with a football field of wetlands vanishing into open water every 30 minutes!  The loss of wetlands across the delta is so severe that communities and infrastructure that were once separated from the open Gulf of Mexico by wetlands are now exposed to open marine water and have become more vulnerable to the damaging effects of storm surge. As a result, the state of Louisiana has developed a series of plans to build new land and infrastructure that would help reduce the net loss of land.  The staggering change between 1932 and 2011 can be seen in the two satellite images below. 

Coastal Louisiana, 2011.  Based on a NASA satellite image, gray and white areas show land and blue indicates open water. New land—mainly coastal improvements such as shoreline revetments and enriched beach areas—that built up since 1932 is shown in green.

Credit: NOAA

Coastal Louisiana, 1932. The image combines the 2011 satellite image with a U.S. Geological Survey map, in which land areas that were present in 1932 are light gray. Since the 1930s, Louisiana's coast has lost 1,900 square miles of land, primarily marshes. Comparing the two maps reveals the dramatic coastal change.

Credit: NOAA