Iron and Trace Metals in Some Tidal Marsh Soils of the Chesapeake Bay
1989
Griffin, Ted | Rabenhorst, M. C. | Fanning, D. S.
Sediments from six tidally influenced Chesapeake Bay marshes were sequentially extracted in order to determine their relative Fe, Zn, Cu, Pb, Ni and Cd content, and to ascertain the relative magnitude of the mechanisms (e.g. adsorption, sulfide occlusion, organic complexation etc., ..) involved in their retention. The extraction sequence used, and the corresponding geochemical phases extracted were: 0.01 M DTPA (exchangeable, organic complexes); 0.1 M HC1 (monosulfide occluded); dithionite citrate bicarbonate (DCB) (Feoxide occluded); H₂O₂ (disulfide occluded, organically bound complexes); HF-HNO₃-HC10₄ (silicate mineral component). The sediments were dated using ²¹⁰Pb geochronology in an effort to evaluate historical rates of metal deposition. Marshes in the vicinity of Baltimore, MD harbor were found to contain relatively higher metal concentrations than those marshes in other areas of the bay thus indicating that the degree of metal contamination is related to the source distance. Rates of deposition were related to historical periods of industrial discharge and to the use of leaded fuels. Iron was retained in the marsh sediments mainly in the oxide and sulfide (FeS₂) phases and was apparently controlled by redox conditions. Copper, Cd and to a lesser extent Zn and Ni were apparently controlled by sulfide precipitation and pyrite coprecipitation thus rendering them noninfluential and unavailable to the marsh biota. Lead however, appears to be weakly complexed by organics and is a potential ecological threat since it is more readily available to plants and organisms and thus may accumulate in the food chain. Contribution no. 7828 and Scientific Article no. A-4807 of the MD. Agric. Exp. Stn. and Dep. of Agronomy, Univ. of Maryland, College Park, MD.
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