EGU2020-665
https://doi.org/10.5194/egusphere-egu2020-665
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

New insights on controls of piping distribution in degraded blanket bog

Taco Regensburg1, Joseph Holden1, Pippa Chapman1, Michael Pilkington2, and Martin Evans3
Taco Regensburg et al.
  • 1University of Leeds, School of Geography, Leeds, United Kingdom (gytr@leeds.ac.uk)
  • 2Moors for the Future Partnership, The Moorland Centre, Edale, United Kingdom
  • 3School of Environment, Education, and Development, University of Manchester, Manchester, United Kingdom

As part of the EU-funded MoorLIFE2020 project, which examines strategies to restore degraded blanket bog in the Peak District of northern England, we investigated natural soil pipes. These pipes are a cause of concern to peatland restoration practitioners who are unsure whether to block them to reduce erosion and flood risk when conducting restoration work. Soil pipes often occur in complex networks with varying channel sizes, undulating through the soil profile. Their prevalence is often linked to controls such as topographic location, slope, aspect, vegetation cover, climate, and properties of the surrounding soil. Such relationships are poorly understood for degraded blanket bog. A before-after-control treatment study was designed to examine the effects of pipe blocking on fluvial carbon removal and streamflow in Upper North Grain (UNG), a small headwater catchment located between 490 m and 541 m above sea level. The catchment has a blanket peat cover up to four meters thick at places, with a branching network of deep gullies that incise into the bedrock. This experimental design was envisaged to address the following hypotheses: (i) the severity of degradation of UNG is a dominant control on pipe density; (ii) blocking of pipe outlets impairs pipe-to-stream connectivity. Our results point towards a rejection of both hypotheses. An initial field survey used to locate and characterize pipe outlets, resulted in 353 individual outlet recordings with a density of 13.79 per km of surveyed gully bank. Southeast, south, southwest and west-facing gully banks accounted for more than 75% of identified pipe outlets. The experimental design compares water and aquatic carbon fluxes in two streams - in one catchment the active pipe outlets (n=25) were blocked by closing off the void behind the pipe outlet with peat and stones, wooden screens or plastic pilling, while in the other catchment the pipes were left open. Areas on the gully bank around original outlets were photographed every two weeks. This analysis showed that within the first month after blocking, all treated pipes had formed bypass routes around the block and initiated new pipe outlets. New outlets were found both above and below the original pipe outlet at distances up to 1 meter from the original pipe outlet regardless of bank aspect, suggesting the networks behind a pipe outlet to be a porous system that connects in both vertical and horizontal directions when issuing onto gully banks. Further results will be presented from the ongoing monitoring showing effects of pipe blocking on streamflow storm responses and the export of particulate and dissolved organic carbon from pipes and streams.

How to cite: Regensburg, T., Holden, J., Chapman, P., Pilkington, M., and Evans, M.: New insights on controls of piping distribution in degraded blanket bog, EGU General Assembly 2020, Online, 4–8 May 2020, https://doi.org/10.5194/egusphere-egu2020-665, 2019

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Presentation version 1 – uploaded on 02 May 2020
  • CC1: Comment on EGU2020-665, Andreas Heinemeyer, 05 May 2020

    Absolutely brilliant work! What an effort !!!

    Did I interprete the veg/bare graph right: more pipes under vegetated peat? Do you have the veg data to look for variables explaining it (is veg drying out the peat more due to evap)? Would be very interesting ... ( but maybe I misunderstood the graph).

    • AC1: Reply to CC1, Taco Regensburg, 07 May 2020

      Hi Andreas, 

      thank you very much. 

      We indeed found more pipe outlets that were surrounded by vegetation than that were surrounded by bare peat. Even at streambanks that are facing the sun directly. We also found more pipe outlets in vegetated sections of the streambank that showed signs of headcut retreat, compared to vegetated streambank sections that had a more uniform outlook.

      two possible reasons:

      1. During the survey we did not account for overhanging vegetation, only later we "reidentified" where pipe outlets were located using a planar aerial image with 10 cm ground resolution. Based on pixel qualification, we made a distinction between bare and vegetated areas, which included the overhanging vegetation at gully edges. So pipe that issued very close to the gully edge, but under the overhanging vegetation, were classified as "in vegetation", whilst in real-life they may still be at the bare surface of the streambank.

      2. streambanks that face the sun, are more susceptible to desiccation, hence the rate at which peat slumps under the vegetation might be higher compared to the opposite facing streambanks. One might argue that this process would steer the growth of shallow bypasses for surface runoff, and hence issue effluent on the streambank, fairly shallow under the edge.     

      • AC2: Reply to AC1, Taco Regensburg, 08 May 2020

        ;to be more precise, the distribution of veg/bare pipe outlets was for edge locations 131 vs 133. only pipe outlets at head locations were more found in vegetated areas, but that seems logical, as to the topographical position you'd expect them

        • CC2: Reply to AC2, Andreas Heinemeyer, 08 May 2020

          Hi Taco,

          Thanks for all this detailed response. Fascinating stuff! I'd love to work more on pipes ... maybe sometime in the future :)