Response of Lagoons to Sea Level Changeby Maynard M. Nichols, Virginia Inst of Marine science, Gloucester Point, United States,
Abstract: Relative sea level change and sediment accumulation rates are compared for 21 lagoons on the U.S. Atlantic and Gulf coasts to determine their accretionary status. The lagoons reviewed exhibit a range of accretionary differences (accumulation minus RSL rate) from a 'surplus' in which accretion exceeds RSL rise to a 'deficit' in which RSL rise exceeds accretion. The majority of lagoons however, have a near balance whereby accretion nearly equals RSL (± 1.6 mm/yr). Where short-term (decades) accretionary differences parallel the direction of long-term (millennia) differences, natural geologic processes of the late Holocene continue to the present day. Marked changes in accretionary differences indicate human intervention of the long-term trends as in Galveston and Mobile Bays. Under accelerated sea level rise, lagoons with an adequate sediment supply are likely to compensate for high submergence rates by increased accretion. However, lagoons with a limited supply are vulnerable. They are likely to shift toward a 'deficit' status and assimilate marshes in the process.
Subject Headings: Lagoons | Sea level | Bays | Sediment | Gulfs | Beach accretion
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