Mineralogy and Related Parameters of Fluvial Suspended Sediments in Northwestern Ohio

Stream water samples were collected weekly for 17 months at eight sampling sites in the Maumee River Basin to characterize the clay mineralogy of the suspended sediments and to determine the utility of mineralogy as a marker of the source (rural, urban, geologic) of the sediments. X-ray diffraction analysis of the clay-sized (< 2 µm) sediments indicated little seasonal or downstream variability in clay mineral composition. The quantities of mica, quartz, and vermiculite-chlorite were 36 ± 5%, 29 ± 5%, and 20 ± 5%, respectively. The quantities of expandables, interstratified, and kaolinite minerals were usually < 10%. The cation exchange capacity (CEC), amorphous, fine clay, and organic matter content of the clay-sized suspended sediments were approximately 44 meq/100 g, 4.4%, 25%, and 5%, respectively. Carbonate minerals were not detected in the clay-sized fraction. The 2 to 50 µm fraction was dominated by quartz in high flow periods and secondary calcite in low flow periods. The stream water was calculated to be saturated with calcium carbonate, thus calcite precipitation could be expected. When fluvial suspended sediment properties were compared to properties of regional soil materials, mineralogy appeared to be a useful index to differentiate between surficial and geologic (parent material) sources of suspended sediments. The clay-sized fraction of the suspended sediments contained percentages of mica and carbonates analogous to local surficial materials yet in contrast to local geologic (parent material) materials. A lack of carbonate minerals in the silt-size (2–50 µm) fraction of the suspended sediments during high discharge events when stream bank erosion, hence geologic erosion, should be maximum further negated the geologic origin of the suspended sediments. The mineralogical characterization of the fluvial suspended sediments in combination with chemical data led to the conclusion that the annual suspended sediment load of the Maumee River and tributaries was predominantly surficial in origin.