The impact of drain blocking on an upland blanket bog during storm and drought events, and the importance of sampling-scale

SummaryOrganic carbon solution and transport processes which occur during periods of heavy rainfall and periods or little or no rainfall, can exert a significant control over a systems’ annual organic carbon budget. In addition, either or both extremes can be key contributors to contaminant release, water discolouration, flood risk or vegetation growth. Although there is an increasing body of work studying hydrological responses to peatland restoration, there are very little available data on the performance of restored peatlands during these key periods. This study builds on previous work from an upland peatland in Wales that has been restored through drain-blocking, and presents evidence from a landscape scale experimental study at the site. A comparison of sampling scales within the study demonstrates the necessity of larger spatial scales, in combination with high resolution datasets, in assessing catchment level responses. Our results suggest that drain blocking leads to higher and more stable water tables that are able to better resist drought periods, and thus lead to more stable discharge from the system. The shallower water tables and pooling in drains also appear to reduce the production and transport of fluvial organic carbon, and thus less organic material is available to be released as during peak flow or dry periods. Despite restoration apparently reducing the available water storage within the peat, the increase in overland flow and in pooling within blocked drains appears to have led to a less flashy system. Peak flow responses in both drains and upland streams are less severe, with more rainfall being retained within the bog. We suggest that restoration leads to a more buffered system, with more moderate responses to extreme events, and reduced release of both dissolved and particulate organic carbon. We discuss the implications of this for fluxes of fluvial organic carbon and sediment loss.

► Restoring peatlands by drain blocking leads to more stable water tables during drought periods. ► These higher water tables led to higher and more stable discharge during droughts. ► Restoration reduces the severity of peak flow responses. ► Restoration reduces the loss of fluvial organic carbon both during and after drought periods.