Constraining rates and trends of historical wetland loss, Mississippi River Delta Plain, south-central Louisiana

The timing, magnitude, and rate of wetland loss were described for five wetland-loss
hotspots in the Terrebonne Basin of the Mississippi River delta plain. Land and water areas
were mapped for 34 dates between 1956 and 2004 from historical National Wetlands
Inventory (NWI) datasets, aerial photographs, and Landsat Thematic Mapper (TM) satellite
images. Since 1956, the emergent land area at the five study areas in south-central Louisiana
has decreased by about 50%. Comparison of the water-area curve derived from the 29 TM
images with water-level records from the nearby Grand Isle, Louisiana tide gauge (NOS
#8761724) clearly shows that changes in land and water areas fluctuate in response to
variations in regional water levels. The magnitude of water-area fluctuations decreased from
the 1980s to the 1990s as former areas of wet marsh within and immediately adjacent to the
wetland-loss hotspots became permanently submerged. The most rapid wetland loss
occurred during the late 1960s and 1970s. Peak wetland-loss rates during this period were
two to four times greater than both the pre-1970s background rates and the most recent
wetland-loss rates. These results provide constraints on predicting future delta-plain wetland
losses and identify Landsat TM imagery as an important source for analyzing land- and
water-area changes across the entire delta plain.