Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Metal distribution, accumulation, and differential mobility were determined in the terrestrial and aquatic portions of Barataria Basin. Seasonal variations in surface water and interstitial pore water constituents of marsh and bay bottom sediments, along a salinity transect were determined through a monthly sampling from March 1984 to August 1985. Diffusion and mass transfer coefficients in bay bottom sediments were determined through the use of non-steady state diffusion cell incubations, and the use of a kinetic silica model, respectively. Sedimentation and particle mixing rates were calculated from the ('137)Cs distribution, and Fe('2+) and Mn('2+) production rates were obtained by applying a one-dimensional transport-reaction model to the solid phase distribution. An iron and manganese mass balance was calculated for bay bottom sediments in the upper and lower portions of the basin. Diagenetic remobilization in the rapidly accumulating bottom sediments of the lower basin resulted in manganese and iron turnover rates of 20 and 40 days, respectively. Increase in ionic strength and benthic fluxes along this salinity transect resulted in significantly higher concentrations of dissolved iron and manganese in the aquatic portions of the lower basin. However, particulate iron and manganese decreased towards the middle and lower parts of the basin due to desorption processes. Partial metal fractionation in water soluble, exchangeable, reducible, and residual phases in marsh and bottom sediments was performed in order to assess and predict the distribution in labile and non-mobile fractions. Saturation states in respect with the main sedimentary solid phases were determined through the use of Geochem, an ion speciation model. Pyrite content, along this salinity transect, was found to be significantly higher in the brackish environments. Dynamic iron and pyrite cycling in the salt marsh resulted in a low pyritic pool (.69% FeS(,2)), characterized as single fine-grained euhedral crystals, indicating its rapid formation. The differential mobility of iron and manganese resulted in a significant fractionation of both metals in the lower basin. Manganese export was restricted to the saline portions of the basin, and an estimated .95 to 1.95 g Mn m('-2) is lost to the Gulf of Mexico every year.

Pages

303

Share

COinS