CHANGES in america's Wetland

"He pointed ahead: 'That used to be a plantation down there - big-big.'  Now it was water.  'She's going fast.'"

                 Harnett Kane, The Bayous of Louisiana, 1943.

". . . this delta division (St. Bernard Parish) has been destroyed as a result of wave action and by sinking."

                 H. J. Chatterton, Development of the Deltas of the Lower Mississippi,  1938.

CONTEXT:  In order to understand trends and futures for America’s Wetland, one must place our knowledge in the context of the normal process of scientific study and analysis.  Coastal wetlands loss has been a serious topic of study only since the late 1970s.  All technologies that are used today have evolved during that short period of time.  Please consult this website for the most current accepted numbers regarding coastal issues.  If you read older studies, realize that discrepancies are due to either changes in how we do the analyses or simply flawed techniques that have been corrected.

Many people who frequented Louisiana's coastal marshes noticed that changes are occurring.  Places that had once been dense marsh were now open water.  There were places where swamps had died and were replaced with salt marsh.  Open bodies of water were getting larger.  Finally, the U.S. Fish and Wildlife Service compared topographic maps of 1956 to those updated in 1978.  For all topo maps in the Louisiana coastal zone, they calculated how much vegetated wetlands existed in 1956, then they did the same on the 1978 updated topo maps.

Buras, LA, USGS quadrangle (topographic)  map for 1956 (dark areas are wetlands vegetation and/or land; white is open water).

Buras, LA, USGS quadrangle map for 1978.  Note the difference!

What they found was staggering!  In just 22 yr, Louisiana had lost an average of 39 sq mi of coastal wetlands per year - marsh changed to open water!

Wetlands loss analysis is vastly improved, and the best information we have is that of the U.S. Fish and Wildlife Service (now part of the U. S. Geological Service) for the period between 1956 and 1978 and a series of Corps of Engineers studies for changes between 1930 and 1990 (Ural and Ural, 1990; Dunbar et al., 1990; Dunbar et al., 1992).   The aforementioned studies' data provided the following information:

These two agencies used somewhat similar methodologies that varied just enough to allow for the 20% or so discrepancy.  USFWS used vegetative cover, floating or rooted; USCOE used only rooted vegetation.

 The truth is that about 39 sq mi per year were lost on the average for each of the 22 yr between 1956 and 1978.  The Corps study found that, for their study period (1983-1990), the rate had dropped to an average of 25 sq mi per year. 

HOW CAN STUDIES BE FLAWED/MISLEADING/WHATEVER?  A map study done for 1993 indicated an accelerated loss of marsh, but further analysis showed that the aerial photos were taken during a strong southeast wind, so much marsh was unnaturally inundated so the conclusions were not valid.

The loss was not the same everywhere along Louisiana's coast.  In some places it was fast, in others, slow.  It tends to be faster in more recently abandoned deltaic regions and slower in the older regions.  This tendency is due to the older ones having already eroded extensively.  At the mouth of the Atchafalaya River, the delta has grown!  Even for a given location, the rate of loss changed from day-to-day, month-to-month, year-to-year.

      The process by which America's WETLAND is being lost is complex.