The most extensive losses in coastal wetlands in the United States over the last two decades have occurred along the Gulf Coast. Wetlands are disappearing at an alarming rate on the Mississippi River Deltaic Plain, indicating a reversal in the trend of net progradation of the delta that characterized much of the past 5,000 years (Gagliano and others, 1981). The land-loss rates have accelerated geometrically during the 20th century, apparently as a result of natural and artificial processes, the latter including artificial levees and control structures that have harnessed the Mississippi River and virtually eliminated the deltaic sedimentation processes of overbank flooding, crevassing, and upstream diversion; extensive canalization and accelerated subsidence related to mineral extraction compound the problem (Gagliano and others, 1981). Investigations of marsh losses in Louisiana indicate that marsh aggradation (vertical accretion) rates are not keeping pace with relative (apparent) sea-level rise (Delaune and others, 1983; Hatton and others, 1983; Baumann and others, 1984; Boesch and others, 1984).
Although less extensive than in Louisiana, losses in wetlands along the Texas coast have also been documented (McGowen and Brewton, 1975; Gosselink and others, 1979; Johnston and Ader, 1983; White and others, 1984; 1985; 1987). Some of the most dramatic changes have occurred in fluvial-deltaic areas such as near the mouths of the San Jacinto and Neches Rivers where wetland losses totaled more than 4,000 hectares (10,000 acres) between the mid-1950s and the late 1970s (White and others, 1985; 1987). The losses are characterized by submergence and displacement of marshes, swamps, and fluvial woodlands by shallow subaqueous flats and open water, indicating, as in Louisiana, that marsh aggradation rates are not keeping pace with relative sea-level rise.Bureau of Economic Geolog
