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Chemical Properties and Mineralogical Characteristics of Selected Dredged Material¹

ABSTRACT

Transporting dredged spoils inland for use in reconditioning adjacent lands marginally suited for agricultural production may be an attractive alternative to other disposal practices. The objective of this study was to evaluate dredged materials (DM) by determining the elemental content and mineralogical characteristics of 10 freshwater and estuarine DM from eastern and central U.S. waterways.

Dredged materials ranged from very acidic (pH 4.7) to alkaline (pH 7.4) in reaction. Acidity was attributed to S^2– and/or Fe²⁺ oxidation resulting when initially reduced sediments were exposed to aerobic conditions. Dredged materials had cation exchange capacity values that ranged from 1.0 to 33.5 meq/100 g. Organic matter contents (5.9–22.5%) accounted for approximately 60% of the variation in the exchange capacity of fine-textured DM. Total N was mainly in organic forms and C/N ratios ranged from 13:1 to 22:1.

Dredged materials exhibited variable accumulations of nutrients and metals reflecting varying degrees of waterway contamination. The levels of Al, Ca, K, Mg, P, and S were generally higher in DM than in reference Minnesota soils. Cadmium, Cr, Ni, Pb, and Zn concentrations in DM were 2 to 6 times, and Cu 20 times, those observed in the reference soils. Manganese concentrations were substantially less in DM than in the soils.

Mineralogy varied with geographical location, contributing watershed, and environmental conditions. All DM contained kaolinite and illite. Amounts of montmorillonite varied because of some conversion to pedogenic chlorite during rapid leaching conditions of sediment drainage. Crystalline Fe₂O₃ was associated with DM clay fractions, indicating precipitation of colloidal-sized hydrous oxide particles and/or surface coatings on clay complexes.

Key Words: heavy metal content • cation exchange capacity • C/N ratio • hydrous oxides

¹ Contribution of the Soil and Water Management Research Unit, USDA-ARS, St. Paul, MN 55108, in cooperation with the Minnesota Agric. Exp. Stn., St. Paul. Sci. J. Ser. no. 11,768. Appreciation is expressed to the U.S. Army Engineer Waterways Exp. Stn., Vicksburg, MS 39180, for partial support of this research.

² Research Assistant, Soil Science Dep., Univ. of Wisconsin, Madison, WI 53706, formerly at Univ. of Minnesota, St. Paul; Soil Scientist, USDA-ARS, St. Paul, and Professor, Univ. of Minnesota, St. Paul; Soil Scientist, USDA-ARS, St. Paul; Soil Scientist, USDA-ARS, St. Paul, and Professor, Univ. of Minnesota, St. Paul; and Chairman, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583, formerly of Soil Science Dep., Univ. of Minnesota, St. Paul.

Received for publication June 8, 1981.