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Preferential Clay Mineral Erosion from Watersheds in the Maumee River Basin¹

ABSTRACT

Runoff sediments and soil surface horizons from five small watersheds were characterized for clay mineralogy, particle size distribution, cation exchange capacity, and amorphous and free iron oxide content. The objective was to determine if preferential transport of clay minerals from these watersheds was occurring.

Clay mineralogical analysis indicated runoff sediments contained higher concentrations of illite and expandables with lower concentrations of vermiculite and quartz relative to watershed soils. The differences were attributed to preferential transport of fine clays from the soil surface.

Runoff sediments contained an average of 18.4% more clay than soil surface horizons. Additionally, the total clay fraction of sediments contained an average of 10.1% more fine clay. Cation exchange capacity increased from 41 meq/100 g for soil clay fractions to 46 meq/100 g for sediment clay fractions due to the increased fine clay content. Both amorphous and free iron oxide contents were lower in the clay fractions of runoff sediments than in the clay fractions of soil Ap horizons.

Key Words: relative erodibility • sediment concentration • particle size distribution • cation exchange capacity • amorphous iron • free iron oxides • expandable minerals • illite • vermiculite • quartz

¹ Contribution from the Dep. of Agronomy, Ohio Agric. Res. and Dev. Center, Wooster (approved for publication as Journal Article no. 25-79) and Ohio State Univ., Columbus. This research was supported by a grant from USEPA and constitutes part of the PLUARG research program.

² Soil Scientist, U.S. Forest Service, Berea, Kentucky; Associate Professor, Dep. of Agronomy, Ohio Agric. Res. and Dev. Center and The Ohio State Univ., Columbus, Ohio; and Professor, Soil and Crop Sci. Dep., Texas Agric. Exp. Stn., College Station, Texas, respectively. The first and third authors were formerly Graduate Research Associate and Professor, respectively, Dep. of Agronomy, OARDC.

Received for publication February 16, 1979.