Spatial and temporal patterns of land-use induced sedimentation in Clear Creek Basin, Iowa

The effect humans can have on the environment is extensive, and is particularly noticeable in agricultural systems. Settlement in eastern Iowa began in the mid to late 1800’s, bringing with it modern agricultural practices, and a converted landscape from the natural prairie and woodland areas that previously existed. Landscape conversion increased erosion, with the sediment eroded and deposited commonly called Post Settlement Alluvium (PSA). This study is centered around the spatial distribution and age structure of PSA in a section of floodplain in the upper reaches of Clear Creek Watershed in east central Iowa. Unfortunately, the past century and a half of Euroamerican land use has negatively influenced the water in Clear Creek, leaving the water not very clear anymore. The study area topography, climate, soil, and pre-settlement tallgrass prairie landcover are representative of the headwaters of many Midwest watersheds, making the findings applicable in other parts of the region. Through this investigation, I aim to further understand the volume, deposition, and distribution of PSA deposited on the floodplain after Euroamericans first settled the area. This employs multiple methods: the collection and measurement of PSA in soil cores, visual and spatial analysis of land use and stream channel morphology, PSA volume calculations, and isotope geochemistry. Using ²¹⁰Lead (Pb) and ¹³⁷Cesium (Cs) isotope geochemistry to calculate age structures of the PSA will provide a more detailed, quantitative understanding of the sedimentation rates, more accurate than model predictions can generate. By understanding the age structure of the sediment on the floodplain, as well as sediment volumes that are stored in floodplain headwaters, we can make tangible connections between agricultural land use and floodplain sedimentation rates and attempt to assess the impact (if any) of potential conservation practices in agriculture, in the past and for the future.