Natural soil pipes are recognised as a common geomorphological feature in many peatlands, and they can discharge large quantities of water and sediment. However, little is known about their morphological characteristics in heavily degraded peat systems. This paper presents a survey of pipe outlets in which the frequency and extent of natural soil pipes are measured across a heavily gullied blanket peat catchment in the Peak District of northern England. Over a stream length of 7.71 km we determined the occurrence and size of 346 pipe outlets, and found a mean frequency of 22.8 km -1 gully bank. Topographic position was an important control on the size and depth of pipe outlets.Aspect had a large influence on pipe outlet frequency, with southwest and west-facing gully banks hosting more than 43% of identified pipe outlets. Pipe outlets on streambanks with signs of headward retreat were significantly larger and closer to the peat surface compared to pipe outlets that issued onto uniform streambank edges. We suggest that larger pipe frequencies are observed on gully banks that are more susceptible to desiccation cracking, and propose that future peatland restoration works could prioritise mitigating against pipe formation by revegetating and reprofiling south and west facing gully banks.

Peatland restoration practitioners are keen to understand the role of drainage via natural soil pipes, especially where erosion has released large quantities of fluvial carbon in stream waters. However, little is known about pipe-to-stream connectivity and whether blocking methods used to impede flow in open ditch networks and gullies also work on pipe networks. Two streams in a heavily degraded blanket bog (southern Pennines, UK) were used to assess whether impeding drainage from pipe networks alters the streamflow responses to storm events, and how such intervention affects the hydrological functioning of the pipe network and the surrounding peat. Pipeflow was impeded in half of the pipe outlets in one stream, either by inserting a plug-like structure in the pipe-end or by the insertion of a vertical screen at the pipe outlet perpendicular to the direction of the predicted pipe course. Statistical response variable η 2 showed the overall effects of pipe outlet blocking on stream responses were small with η 2 = 0.022 for total storm runoff, η 2 = 0.097 for peak discharge, η 2 = 0.014 for peak lag, and η 2 = 0.207 for response index. Both trialled blocking methods either led to new pipe outlets appearing or seepage occurring around blocks within 90 days of blocking. Discharge from four individual pipe outlets was monitored for 17 months before blocking and contributed 11.3% of streamflow. Pipe outlets on streambanks with headward retreat produced significantly larger peak flows and storm contributions to streamflow compared to pipe outlets that issued onto straight streambank sections. We found a distinctive distance-decay effect of the water table around pipe outlets, with deeper water tables around pipe outlets that issued onto straight streambanks sections. We suggest that impeding pipeflow at pipe outlets would exacerbate pipe development in the gully edge zone, and propose that future pipe blocking efforts in peatlands prioritize increasing the residence time of pipe water by forming surface storage higher up the pipe network.

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.

<p>A better understanding of soil erosion is not possible without including subsurface erosion. Soil piping may significantly contribute to the overall erosion problem in a given area and may therefore change the conditions and methods for controlling soil degradation. Therefore, there is an urgent need to identify regionally and globally sites where soil piping occurs which then may require a change of the strategies to control soil erosion. In this project, we are constructing the very first data-driven piping erosion susceptibility map of Europe. The crucial point is to identify piping-affected areas by mapping the soil piping-related features, i.e. pipe roof collapses (PCs) and pipe outlets in the European Union and the UK. Mapping is based on an in-depth literature review in combination with detailed mapping using Google Earth imagery, and LiDAR data (if available). The database currently consists of 6841 piping-related features (6171 PCs, and 670 outlets), among which the location of 88% features is certain (within a resolution of 25 m). Almost 28% (1889 features) were located based on detailed fieldwork, 25% (1726) were extracted from published papers, and 47% based on a detailed analysis of Google Earth imagery and LiDAR data (19% and 28%, respectively). This database is currently used to construct the very first data-driven piping erosion susceptibility map of Europe.</p><p> </p><p>This research is part of the project “Building excellence in research of human-environmental systems with geospatial and Earth observation technologies” that received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 952327.</p>

<p>Piping erosion leads to land degradation and causes several environmental and societal problems, although this process is rarely considered in soil erosion studies. So far, there are no systematic studies at regional to global scales aiming to understand the patterns and controlling factors of soil piping. This is mainly due to the methodological challenges related to detecting soil pipes. With this project, we aim to address this gap by identifying piping-affected areas in Europe. For this, we are constructing a database on surface evidences of soil piping, i.e. pipe roof collapses (PCs) for the European Union and the UK. Locations and other details of PCs in this database are collected based on an in-depth literature review in combination with detailed mapping based on Google Earth imagery, ortophotos and LiDAR data (if available). While the work is still ongoing, we have already compiled information on >2000 PCs in 10 different countries. In a next phase, we will use this PC database to construct the very first data-driven piping erosion susceptibility map of Europe.</p><p>This research is part of the Twinning project “Building excellence in research of human-environmental systems with geospatial and Earth observation technologies” that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 952327.</p>