Connectivity has become an important conceptual and practical framework for understanding and managing sediment transfers across hillslopes, between hillslopes and rivers, and between rivers and other compartments along the river corridor (e.g., reservoirs, channel substrate, and floodplain). Conventionally, connectivity focuses on the quantity of sediment transferred but here, we also consider the size of the finer sediment (typically particles <500 μm diameter). We examine the role of small rapidly silting reservoirs in the river Rother on storing sediment and disrupting downstream sediment transfers. Spatial and temporal changes in the particle size characteristics of sediment deposited in one of the ponds is explored in detail. Downstream of this pond, we collected sediment from the river on nine occasions over 17 months using two sampling methods at two locations; first, immediately downstream of the pond and a second ~700 m further downstream but upstream of the confluence with the Rother. Results showed a significant depletion in sand‐sized particles immediately downstream of the pond but the sand had been recovered from an in‐channel source before the river reached the downstream sampling point.

Abstract. The River Rother, West Sussex, is suffering from excess sediment which is smothering the river bed gravels. This is thought to be exacerbating issues of pollution and degradation of ecosystems. This project aims to identify the severity, extent, possible causes and potential mitigation options available to reduce these pressures on the river. Data have been collected from ten sites to investigate the amount of sediment stored in the river bed gravels and cores obtained from four small reservoirs to establish rates of sedimentation and contribute to the construction of a temporal sediment budget over the last 50-100 years. Evidence suggests that tributary streams have more stored sediment per m 2 upstream of their confluence with the River Rother compared to the Rother itself. Reservoir core data indicate that sediment has accumulated more rapidly in the small reservoirs surrounded by mixed agricultural land compared to one surrounded by ancient woodland. These are preliminary results and work is continuing.

Farm ponds, reservoirs and in‐stream weirs exist in most lowland UK river catchments and often dominate natural features such as lakes, wetlands, floodplains and debris dams. Artificial structures have served multiple purposes, including provision of power for historic flour milling and iron ore crushing and provision of water for medieval fishponds, canals, crop irrigation and potable supply. Although unintentional, they can significantly affect longitudinal connectivity, including sediment delivery pathways, through river catchments. We report results from three spatially nested case studies that were undertaken in the Rother catchment, ranging in scale from small farm ponds of a few square metres in area, to larger in‐stream weirs and reservoirs (locally called ponds). Reservoirs typically trap sediment, decreasing sediment availability downstream, while inducing valley sediment accumulation upstream. We focus on the quantity and particle size characteristics of sediment trapped behind these structures compared to catchment soils and to sediments that are transported through, and deposited in, ‘natural’ gravel‐bed reaches. At all scales our results demonstrate that sediment trapping and release are particle size specific. Fine to coarse sands (125 μm to 2 mm diameter) and coarser sediments are retained behind structures at all scales, while silts and clays (<63 μm diameter) and organic matter are generally depleted in the stored sediment. Even though 75% of the surveyed reservoirs have very low estimated trap efficiencies (<5%), they slowly fill over time with sediment. An important management question relates to the likely benefits of impoundment, structure or sediment removal, and whether fine (here defined as <63 μm) or coarser (>63 μm) sediment is a priority for management.

137 Cs has been extensively utilised for the investigation of catchment sediment dynamics. Its activities can be indicative of sediment derived from surface sources and its inventories in deposited sediments are representative of local fallout, sediment accumulation rate and sediment source. Lakes represent ideal depositional environments for the reconstruction of historical sediment dynamics. In the UK, 137 Cs depth profiles and inventories of lake cores have been investigated in a large number of catchments but no study has attempted to synthesise all of this data to identify national trends. The aim of this study was therefore to determine what can be learnt from the 137 Cs inventories and profiles in UK lakes currently available. Analysis revealed that local reference fallout, the rate of sediment deposition (cm yr-1) and the lake-catchment area ratio, are the most important factors controlling lake 137 Cs inventories. However, mobile 137 Cs delivery to the lake shortly after fallout dissolved in runoff or in association with mobilised sediment in transit from source towards the lake are also major controls on the inventories and especially on the down-core profiles. In the present day, it is suggested that dissolved 137 Cs inputs remain major controls on the corresponding activities of recently deposited sediments as they are often higher than potential contributing catchment sediment sources. Despite this uncertainty, 137 Cs depth profiles can provide information on sediment sources and dynamics when interpreted carefully in the context of other lakes in the UK and catchment characteristics. Several distinctive down-core profiles and unexpected inventories evaluated by the work reported here yielded valuable insight into catchment sediment dynamics.