Aquatic carbon concentrations and fluxes in a degraded blanket peatland with piping and pipe outlet blocking

Soil piping is an important agent of erosion in many environments, including blanket peatlands. Peatland restoration that aims to reduce erosion has mainly focussed on revegetation and blocking ditches and gullies, rather than reducing erosion from natural soil pipes. However, little is known about the contribution of pipeflow to the fluvial carbon budget of degraded blanket peatlands and whether it is possible to moderate it. In a heavily degraded blanket bog, dissolved and particulate organic carbon (DOC and POC), and water colour, from two catchments were compared before and after half of the pipe outlets in one catchment were blocked. One blocked pipe was monitored for discharge and water quality both pre- and post-blocking as new pipe outlets had formed around the blocked outlet. Both pre- and post-blocking, maximum concentrations of DOC and POC were markedly higher in pipe-water than stream-water, with ratios of 1.2 (pre) and 1.3 (post) for DOC, and 4.8 (pre) and 8.8 (post) for POC, rendering pipe-to-stream transfer more effective for DOC than POC due to the deposition of POC close to pipe outlets. The increase in DOC and POC flux post-blocking in both catchments was near-identical, suggesting pipe outlet blocking was ineffective in reducing fluvial carbon export from pipe networks. Extrapolation of pipe fluxes to catchment scale showed pipes potentially contribute c. 56% of DOC exported by the stream, and that more POC was produced by pipes than was exported by the stream. Our work highlights that pipes need to be considered when seeking to reduce fluvial carbon export in degraded blanket peatlands.