Papers by Bedosky, S.J.

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Bedosky, S.J. . 1987. Recent sediment history of Apalachicola Bay, Florida.. Florida State University: 247.
The Apalachicola River Delta is the depositional terminus for sediments carried by Florida's largest river. This river, in conjunction with the Flint and Chattahoochee Rivers, forms a watershed that drains 58,000 km2 of Alabama, Georgia and Florida. During the past 150 years both man and nature have had significant effects on the river system and bay. Over 90% of the land is presently devoted to timber farming and agriculture. The Apalachicola River has been dredged periodically since 1857. Between 1952 and 1963, II dams have been constructed on the three rivers. The purpose of this project is to determine what effect these alterations have had on sedimentation in the active delta and to delineate correlative sedimentary horizons within the recent sediments. Twelve cores, averaging one meter in length, were collected from the various sedimentary sub-environments of the delta and estuary. Down-core magnetic susceptibility and clay mineral profiles were compiled for each core. Pb-210 radiometric analyses were obtained on 4 cores to determine sedimentation rates. These data were supplemented with bathymetric digitization data from 3 historic charts of East Bay. Fluorescent tracer sands were emplaced in 18 locations to determine short-term sedimentation rates, hydrodynamic conditions and the extent of sediment mixing. The clay mineralogy data showed kaolinite to be the most abundant mineral in the bay, commonly comprising 70% of the suite. Smectite was next in abundance and generally represented 20% of the clay mineral suite. Quartz and muscovite were present in minor proportions. The down-core clay mineral profiles showed no long-term variations. The Pb-2l0 down-core radiometric profiles contained a break in slope at mid-depth, indicating a change in sedimentation rate which occurred sometime during the last three decades. Sedimentation rates for the active delta averaged 7 mm/yr. This value is similar to that determined by bathymetric digitization: 2.3 mm/yr was calculated for all of East Bay. This smaller value should be expected for the larger, less active area. The average linear progradation of the delta distributaries was found to be slightly over 2 m/yr. Magnetic susceptibility values for each interval were found to be directly related to the coarse grain fraction for that interval. Three distinct patterns were delineated in each profile, providing useful information for correlating between cores. The magnetic susceptibility data support the clay mineral data in that no long-term variations occurred down core. Cores which penetrated the fluorescent sand patches provided limited but useful information. One core contained a sediment mixing layer which was 9 cm thick. This value is very similar to those determined in the Pb-210 radiometric analysis. Two cores contained more than 1 cm of sediment deposited above the fluorescent sand layer, over a five-month period. This indicates rapid short-term sedimentation in places, especially during a period without storm activity. I The data reported herein indicate constant long-term sedimentation characteristics. The emplacement of aII dams on the three-river system may be correlated to variations in sediment characteristics but seem to have had no long-term effects in the delta. The rapid rate of sediment accumulation and lack of appreciable submergence will ultimately lead to the complete infilling of the bay within the next few centuries.
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