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ABSTRACT: Seagrass Sediment Particle-Size and Content in Estero Bay, Southwestern Florida

MITCHELL-TAPPING, HUGH J., Estero Bay Marine Laboratory, Fort Myers Beach, FL; and JOSEPH P. MELLON, Florida Gulf Coast University, Fort Myers, FL

Grain size and content analyses was made of the top 0.5 m of sediment from 33 cores taken across 3 species-specific seagrass beds in Estero Bay Aquatic Preserve, southwestern Florida during 1999. The seagrass beds contained some algae with abundant Thalassia, Halodule, and Thalassia-Halodule mixed, respectively, while the sediment was composed of varying amounts of quartz sand, silt-sized quartz, and carbonate skeletal particles, with small admixtures of larger shell fragments, organic remains, silt, and clay. The average particle size is about 0.25 mm with grain size modes at 0.3 and 0.1 mm. These sediments are fairly well-sorted (medium standard deviation), positively skewed (excess fine particles) and are leptokurtic (moderate peakedness). Comparison of sediment from different species of seagrass reveals a difference in terms of pan size characteristics. There is a significantly higher content of silt in Thalassia and Thalassia-Halodule bed sediments than in Halodule beds. This species-specific preference difference may not be due to wave-energy and sediment-size alone, but may also be due to freshwater runoff influence.

Sediment-trap collections for 5 months during Summer and Fall of 1999, the wet and storm season in southern Florida, give a particle flux ranging from 1020 g/diem that increased during periods of high winds, due to the very shallow nature of the bay (<1 meter). During the dry season of 1999/2000 the flux range was lower. It is not known how much of this flux has come from local resuspension of sediment particles or direct imput from the Gulf of Mexico.



AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas