Evaluating the effectiveness of soil conservation at the basin scale using floodplain sedimentary archives

Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of advanced soil management strategies for riverine catchments. The fertile catchment of the River Avon (Southwest, England) has natural and anthropogenic impacts that require enhanced definition aiding the development of a catchment management plan. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Sediment samples were collected in each unit as surface soils and four cores were obtained along the floodplain. The samples were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates (SARs) were affected by the construction of a reservoir, whereby the distributions of silt and clay in the floodplain were most affected over the past 60 years. Fertilizer components, Cr and P, were correlated in the mid-catchment, which unraveled downstream due to elevated concentrations of Cr from a geological source. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements were evaluated, quantitatively, using a Bayesian Mixing Model. The statistics showed that cultivated land made a significant contribution to the sediment mixtures, independent of space and time. The results contribute to improvements in soil quality and soil conservation measures for the Avon which maybe applicable to other small catchments in the UK and elsewhere.