Use of floodplain sediment cores to investigate recent historical changes in overbank sedimentation rates and sediment sources in the catchment of the River Ouse, Yorkshire, UK

Abstract

Floodplain sediment cores collected from seven sites in the catchment of the River Ouse, in Yorkshire, UK, have been used to provide information on recent historical changes in both rates of overbank sedimentation and sediment sources. The environmental radionuclides 137 Cs and unsupported 210 Pb have been used to establish chronologies for each core and to estimate average sediment accumulation rates for the last ca. 30 and 100 years, respectively. Average sedimentation rates for the individual cores ranged from 0.11 to 1.04 g cm −2 yr −1. In all but one case, the estimates of average sedimentation rate during the last ca. 30 years for the individual cores are broadly similar to those for the last ca. 100 years, suggesting that overbank sedimentation rates have been essentially uniform over the longer time period. Composite fingerprints, based on a combination of geochemical and mineral magnetic properties, and a numerical mixing model have been used to investigate downcore changes in sediment source. In the case of source type, most of the cores reflect a primarily topsoil source, although there have been periods with increased contributions from subsoil/channel bank sources. Within the Ouse basin in general, the period commencing in the late 19th and early 20th century and extending through to the 1960s, was characterised by increased contributions from topsoil sources. However, contributions from subsoil/channel bank sources have increased over the last few decades. The source tracing results relating to sediment contributions from the three main geological/topographic zones are in broad agreement with the proportion of the area of the catchment underlain by each rock type. Temporal variations in the contributions from the three geological/topographic zones vary from site to site, but for the lower reaches of the River Ouse contributions from areas underlain by Permian and Triassic rocks, which mainly outcrop in the Vale of York, have increased since the turn of the century. The changes in sediment source identified are probably a reflection of changes in land use and management (and possibly changes in climate). These results enable estimates of contemporary suspended sediment fluxes and sources to be placed into a historical context and provide a means of considering the likely impact of potential future changes in land use and climate in the study basin.