Late Holocene coastal wetlands change, Mississippi Sound, Alabama: Short-term vs. long-term patterns and processes
- Geological Survey of Alabama, Tuscaloosa, AL (United States). Environmental Geology Div.
Wetlands occupy much of the low-lying mainland coast in Mississippi Sound, Alabama, grading from Spartina salt marsh (48.8 km[sup 2]) to fresh water marshes (13.5 km[sup 2]) to forested wetlands (123.4 km[sup 2]) (Rathbun et al, 1987). These wetlands are undergoing rapid short-term (years to decades) net acreage loss due to headland shoreline erosion. In contrast, long-term (centuries to millennia) change in marsh area is largely due to submergence from Holocene transgression and local subsidence. The Sound overlies drowned Pleistocene-Holocene coastal sediments; existing salt marshes likely developed after inundation of paleomarshes cored at a MHW depth of [minus]3 to [minus]7 m in the mid-Sound (C[sup 14] dates of 4--7,000 Y.B.P.). Geomorphic evidence indicates the primary cause of short-term loss of salt marsh is localized erosion of its seaward edge, rather than submergence. A low (< 1 m) intertidal scarp and narrow sandy beach on open Sound shorelines indicate episodic storm erosion. Linear open Sound shorelines formed by wave modification, in contrast to typically less modified protected shores; nearshore Sound bathymetry shows a gently seaward sloping possible wave-cut terrace. Marsh erosion rates are due to several processes including water energy (background as well as seasonal storms); cohesiveness of marsh sediments; and health of marsh flora. Orientation of the shoreline relative to southerly wind-forced waves during passage of winter cold fronts may be the primary factor. While today's short-term rates of overall vertical coastal inundation are relatively low, the development of new marsh acreage is also negligible. As sediment influx from coastal streams is low, it may be difficult to sustain present marsh acreage should sea level rise accelerate.
- OSTI ID:
- 6762534
- Report Number(s):
- CONF-9404221-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 26:4; Conference: 43. annual meeting of the Southeastern Section of the Geological Society of America, Blacksburg, VA (United States), 7-8 Apr 1994; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
Similar Records
Role of salt-marsh erosion in barrier island evolution and deterioration in coastal Louisiana
Epicontinental sea-margin development on the contemporary Florida Platform
Related Subjects
ALABAMA
WETLANDS
GEOMORPHOLOGY
MONITORING
EROSION
GEOLOGIC HISTORY
SHORES
AQUATIC ECOSYSTEMS
COASTAL REGIONS
DEVELOPED COUNTRIES
ECOSYSTEMS
GEOLOGY
NORTH AMERICA
USA
540210* - Environment
Terrestrial- Basic Studies- (1990-)
540310 - Environment
Aquatic- Basic Studies- (1990-)