Making connections: Changing sediment sources and sinks in an upland catchment

摘要

The effect of changes in catchment processes and conditions can be studied by using connectivity as a framework for understanding the feedbacks and interactions occurring within the system. The sediment record preserved in reservoirs can be a useful archive of catchment changes, but needs to be considered in conjunction with the different elements that compose and act on the system to take into account its complexity. Changing patterns of connectivity have been studied in the Ingbirchworth Catchment (Yorkshire, UK), using a multiple methodology approach combining the analysis of reservoir-sediment records with knowledge of recent land-use history, high resolution rainfall records, catchment characteristics and management aspects. Sedimentation rates inferred from reservoir-sediment cores from two reservoirs in the Ingbirchworth catchment show sedimentation peaks which coincide with periods of significant changes in the catchment, such as the introduction of arable crops, the establishment of land drainage and the widespread intensification and mechanization of agriculture. Rainfall patterns, including combinations of events such as droughts and increased precipitation, contribute to increased sediment transfer under catchment conditions in which more sediment and/or new pathways are made available due to catchment changes. Sediment fingerprinting supports the notion that changes in sedimentation rates are not just related to increased/reduced erosion and transport in the same areas, but also to the establishment of different pathways increasing sediment connectivity. The results demonstrate that typical calculations of catchment-area yields are not sufficient as sediment-contributing areas vary as a consequence of changing conditions. The study provides insights into the complex interactions influencing connectivity, such as the relation between catchment changes and climatic inputs, and the subsequent effect on catchment conditions and transfer networks.