DETERMINATION OF SEDIMENT PROVENANCE IN AN URBANIZED STREAM, BRUSH CREEK, KANSAS CITY, MO

Flooding and non-point source pollution are two serious problems in urban streams. Sedimentation can both reduce channel capacity and provide a vector and sink for various contaminants, possibly increasing the effects of flooding and pollution. Identification of the local sources of sediments can be used to help mitigate potential sediment influx. Sedimentary petrography, mineralogy, and trace-element geochemistry of the <2mm fraction were used to identify local sediment sources along Brush Creek. Potential sources include limestone and shale outcrops, loess (used as construction fill), and soils (residual and loessal). Weathering limestones contribute euhedral dolomite rhombs, along with small anhedral calcite grains and fossils. Black or gray shales are represented by flakes of lithic fragments mainly in the coarse sediment fractions. Loessal contributions are evident as uniformly-sized angular grains of quartz and feldspar. Local soils contain angular grains of quartz and feldspars (loessal contribution), and variably-rounded detrital grains of hornblende, tourmaline, garnet, zircon, and titanite. The creek's bed-load mineralogy is most similar to that of local soil. Source discrimination is based on trace element geochemistry using ternary plots of normalized element contents, including Zn+Cu+Cd, Ni+Co+Cr, Mo+Sb+As, and Ba+Th. Most trace elements show the least amount of difference between the sediment and local soil, and then the second least amount of difference between soil and loess, reflecting the loessal origin of some of the local soils. The abundances of REE, as well as the patterns between the sediments and the local soils are similar, yet distinctly different from those of the other potential sources. The insignificant compositional differences between sediment and bank soil indicate that bank soil is the major contributing zone for fine sediments in Brush Creek. Mobilization of bank soil by storm events and anthropogenic disturbance appears to be the most important process for introducing sediment to the stream. This process impacts on contaminant transport and fate. Consequently, municipal policies and codes should be designed to minimize natural and anthropogenic erosion and sediment-laden runoff within the drainage basin.