TEMPORAL AND SPATIAL TRENDS IN THE PARTICLE SIZE DISTRIBUTIONS OF HOLOCENE AND LATE PLEISTOCENE PALEOCHANNEL DEPOSITS, FOUR MILE CREEK, SOUTHWESTERN OHIO

Stream restoration is a method used to try to return function to impaired streams and has become a billion-dollar industry in the U.S. The goals of stream restorations often include sediment load reduction or diversifying aquatic habitat. Determining the particle size distribution of paleochannel deposits prior to widespread land-use changes, and then assessing the natural spatial and temporal variations of these paleochannel deposits, provides baseline stream characteristics that could improve the success of stream restoration projects.

We conducted exploratory research along Four Mile Creek in southwestern Ohio to assess if Holocene and Late Pleistocene aged paleochannel deposits preserve quantifiable changes in D₅₀ particle size and percent mud (<63 microns) temporally and spatially. A total of nine gravel samples were collected from paleochannel deposits exposed along Four Mile Creek whose ages had been determined through radiocarbon analysis or georeferenced historic atlases. Samples were then dry sieved in the lab and analyzed using GRADISTAT software. Single-factor ANOVAs were conducted to assess D₅₀ particle size and percent mud variations over three time periods. T-tests were then used to assess D₅₀ particle size and percent mud variations between sites located upstream and downstream of a bedrock knickzone.

D₅₀ particle size analysis did not reveal any significant differences between the three time periods (p=0.806) and all samples had D₅₀ values that were within the Wentworth size class of “pebble”. However, the percentage of mud in the paleochannel deposits was significantly higher in those that post-dated European colonization (p=0.010). No spatial trends were identified in relation to samples upstream versus downstream of the bedrock knickzone for either D₅₀ particle size (p=0.255) or percent mud (p=0.655). This study provides a baseline understanding of how D₅₀ particle size and percent mud has changed temporally and spatially in the watershed and provides strong evidence for the increase in fine sediment load during the historic period.