Soil texture and vegetation root density assessment on regulating erosion across river floodplains

Over the last few decades, floodplain management with best management practices has been utilized to treat areas susceptible to soil erosion and degradation. A major emphasis has been placed on the role of the above-ground vegetation to regulate soil erosion, but less attention has been directed to the floodplain soil types and root interactions. The goal of the current study was to quantify the effectiveness of soil texture and vegetation root density in reducing soil erosion in the highly agricultural Turkey River watershed in Iowa. For the purposes of this study, twenty-four topsoil samples were removed from various locations across the lower, i.e., active, and higher elevation river floodplain soils of five identified field sites along the Turkey River longitudinal profile. The topsoil sampling process was designed based on site-specific flood inundation maps. Using detailed particle size analyses and topsoil erodibility experiments, results indicated that the threshold values for the onset of erosion increased longitudinally, from upstream to downstream, matching the pattern identified for silt and clay particles in floodplain soils. Statistical analysis confirmed that there is a strong linear correlation between the threshold values for erosion to occur and the fine particle content in floodplain soils, as well as the existence of vegetation characterized by dense and well-developed root systems. Overall, the fine particle content of floodplains’ surface soils and the existence of vegetation with dense and well-developed roots determined the threshold values for erosion, whereas the presence of vegetation with non-dense and non-well-developed root systems had a negligible effect, similar to bare soil, on controlling soil erosion. The findings of the current research can be applied by watershed management authorities to protect floodplain areas at risk and prevent further soil degradation and water pollution.