Peat erosion: processes, patterns and rates

Improved understanding of peat erosion processes and rates of erosion at different scales are urgently needed to better predict future peat erosion under climate and land management changes. This laboratory and field study on UK blanket peat showed that both raindrop impact and the interaction between rainfall and flow driven erosion processes were important in affecting peat overland flow and erosion processes for gentle slopes and shallow overland flow conditions. Raindrop impact contributed significantly to increasing sediment yields (47%). Needle-ice (NI) processes dramatically increased peat erodibility and reduced peat stability, producing six times higher peat losses than control treatments. NI significantly reduced surface flow velocity (32–44%) but increased overland flow shear stress (55–85%). Net topographic change measured using Structure-from-Motion (SfM) was –14 to +30 mm yr–1 for field plots (peat hagg, gully wall, riparian area, gully head) and –27 mm yr–1 over a 598 m2 catchment. Repeated SfM surveys showed spatial patterns of erosion and deposition could be driven by event-scale processes that may not be observed with surveys conducted between long intervals. Surface roughness was a significant predictor of topographic change at both field plot scale and laboratory macroscale. SfM produced significantly different topographic change values compared to sediment traps in nested catchments in the field and sediment yield sampling on laboratory peat blocks. The greatest sediment and particulate organic carbon losses from a 1.7 ha study catchment were found during the autumn and much of the available sediment appeared to be derived from weathering during dry weather earlier in the year. The research shows that where bare peat is subject to weathering by needle ice and desiccation, and is subsequently splashed by raindrops a large supply of sediment can be mobilised by overland flow, particularly where flow concentrates producing interrill, rill and gully erosion.