Quantifying Anthropogenic Disturbances Caused by Changing Land-cover and Climate in the River Thames, UK.

Understanding the effects of natural and anthropogenic disturbances on sediment and nutrient dynamics in lowland rivers is important in building resilient strategies to manage environmental change. Many changes in the river environment can be considered disturbances, but the effects of land-cover change on sediment and nutrient dynamics are poorly understood, especially in the context of changing climate and river management. Here we use a low-frequency suspended sediment sampling dataset to assess the spatial and temporal variations of sediment fluxes in the River Thames (UK). Our approach uses a sediment rating curve (SRC) to analyse both the spatial and the temporal variation of catchment erodibility and sediment transport. First, the variations in SRC parameters in several sub-catchments are assessed and related to environmental factors including land cover, geology and vegetation. Then, the seasonal and inter-annual variability of SRC parameters are analysed to reveal seasonal and secular changes associated with urbanization and changing land management practices. Lastly, a simple dynamic SRC model for the estimation of sediment transport in the Thames was implemented and evaluated against observations. The results quantify the spatial variability of sediment transport within the catchment and reveal a seasonal flushing effect, in which sediment loads are typically substantially higher during the first floods after the summer dry period. We estimate that, for the River Thames, the sediment loads of the first floods after summer are around double that of other floods. We observed a decrease in the flushing effect which began in the late 1990s.