Microtopography of bare peat: a conceptual model and objective classification from high‐resolution topographic survey data

Abstract

Peatlands globally are at risk of degradation through increased susceptibility to erosion as a result of climate change. Quantification of peat erosion and an understanding of the processes responsible for their degradation is required if eroded peatlands are to be protected and restored. Owing to the unique material properties of peat, fine‐scale microtopographic expressions of surface processes are especially pronounced and present a potentially rich source of geomorphological information, providing valuable insights into the stability and dominant surface process regimes. We present a new process‐form conceptual framework to rigorously describe bare peat microtopography and use Structure‐from‐Motion (SfM) surveys to quantify roughness for different peat surfaces. Through the first geomorphological application of a survey‐grade structured‐light hand‐held 3D imager (HhI), which can represent sub‐millimetre topographic variability in field conditions, we demonstrate that SfM identifies roughness signatures reliably over bare peat plots (<1 m2), although some smoothing is observed. Across 55 plots, the roughness of microtopographic types is quantified using a suite of roughness metrics and an objective classification system derived from decision tree analysis with 98% success. This objective classification requires just five roughness metrics, each of which quantifies a different aspect of the surface morphology. We show that through a combination of roughness metrics, microtopographic types can be identified objectively from high resolution survey data, providing a much‐needed geomorphological process‐perspective to observations of eroded peat volumes and earth surface change. Copyright © 2018 John Wiley & Sons, Ltd.

Patterns and drivers of peat topographic changes determined from Structure‐from‐Motion photogrammetry at field plot and laboratory scales

“…First, a significant relationship between topographic change and surface roughness was observed consistently at both the field plot scale (Table V) and laboratory macroscale (Table VIII). The main reason is probably that both the topographic change and roughness of bare peat surfaces are driven by key natural drivers (rainfall, surface wash, wind action, needle-ice production and desiccation) that take place at event-scales (Evans and Warburton, 2007;Smith and Warburton, 2018). The main reasons are: (i) an increased roughness of bare peat surfaces has important feedbacks on sediment transport mechanisms by reducing overland flow velocity; and (ii) surface roughness at the studied small scales provides insights into the erosion agents (e.g., wind-driven rain, surface wash, frost action and desiccation) and the relative magnitude and direction of the sediment transfer process (Evans and Warburton, 2007;Smith and Warburton, 2018).…”

“…In future, a more detailed understanding of the processes driving observed erosion and deposition patterns could be informed by a segregation of the sediment budget according to the driving process, achieved either by visual inspection, analysis of localized volumetric changes (Wheaton et al, 2013) or roughness analysis (Smith and Warburton, 2018).…”

“…Roughness was positively correlated to the positive topographic change; and was negatively correlated to negative topographic change. The main reasons are: (i) an increased roughness of bare peat surfaces has important feedbacks on sediment transport mechanisms by reducing overland flow velocity; and (ii) surface roughness at the studied small scales provides insights into the erosion agents (e.g., wind-driven rain, surface wash, frost action and desiccation) and the relative magnitude and direction of the sediment transfer process (Evans and Warburton, 2007;Smith and Warburton, 2018). In addition, this study highlights the importance of roughness in particular for short-term surveys during which needle-ice production, desiccation and rainsplash and surface wash take place.…”

“…However, to the best of our knowledge, there are only two studies that have been reported using and testing the application of SfM techniques in peatlands. Smith and Warburton (2018) used groundbased SfM surveys to quantify roughness for different peat surfaces and found that SfM reliably identified roughness signatures over bare peat plots (< 1 m 2 ). They found that GB-SfM was the best of the three techniques at measuring the volumes of erosion features at fine spatial resolution.…”

“…They found that GB-SfM was the best of the three techniques at measuring the volumes of erosion features at fine spatial resolution. Smith and Warburton (2018) used groundbased SfM surveys to quantify roughness for different peat surfaces and found that SfM reliably identified roughness signatures over bare peat plots (< 1 m 2 ). However, despite the application of new peat surveying techniques there has been a lack of their use to specifically understand spatial and temporal peat erosion dynamics or processes in a range of peatland environments.…”