Identification of typical eco-hydrological behaviours using InSAR allows landscape-scale mapping of peatland condition

Abstract

Abstract. Better tools for rapid and reliable assessment of global peatland extent and condition are urgently needed to support action to prevent their further decline. Peatland surface motion is a response to changes in the water and gas content of a peat body regulated by the ecology and hydrology of a peatland system. Surface motion is therefore a sensitive measure of ecohydrological condition but has traditionally been impossible to measure at the landscape scale. Here we examine the potential of surface motion metrics derived from InSAR satellite radar to map peatland condition in a blanket bog landscape. We show that the timing of maximum seasonal swelling of the peat is characterized by a bimodal distribution. The first maximum is typical of steeper topographic gradients, peatland margins, degraded peatland and more often associated with ‘shrub’-dominated vegetation communities. The second maximum is typically associated with low topographic gradients often featuring pool systems, and Sphagnum dominated vegetation communities. Specific conditions associated with ‘Sphagnum’ and ‘shrub’ communities are also determined by the amplitude of swelling and average multiannual motion. Peatland restoration currently follows a re-wetting strategy, however our approach highlights that landscape setting appears to determine the optimal endpoint for restoration. Aligning expectation for restoration outcomes with landscape setting might optimise peatland stability and carbon storage. Importantly, deployment of this approach, based on surface motion dynamics, could support peatland mapping and management on a global scale.

Multiscale Variability and the Comparison of Ground and Satellite Radar Based Measures of Peatland Surface Motion for Peatland Monitoring

“…On the other hand, steeper and shrub dominated sites surface height peaks earlier during both pre and post drought conditions. Ground measurements show considerable variability in the amplitude of these seasonal oscillations which also replicates observations made from satellite radar [7]. The timing of and recovery time following extreme climate events such as observed during the 2018 European Drought event was also reproducible between ground and satellite radar measures in this study.…”

“…At the landscape unit scale, ground-based leveling data support the bimodal distribution in peak timing observed and derived from InSAR data [7]. It also supports the broad ecohydrological relationships with peatland motion identified by [1,7,32], namely that in wetter and lower gradient, Sphagnum dominated parts of the ecosystems surface height peaks during winter. On the other hand, steeper and shrub dominated sites surface height peaks earlier during both pre and post drought conditions.…”

“…The raw data used in this study and a detailed description of the processing protocols used are available at [37]. The InSAR data used in this study is the same as used by [7] for large-scale condition mapping in the Flow Country and [5] to assess restoration outcomes.…”

“…Recent developments in the use of Satellite Interferometric Synthetic Aperture Radar (InSAR) to measure seasonal oscillations of peatland surface at the site and landscape scale have been shown to be highly diagnostic of peatland character and condition [1][2][3][4][5][6][7][8]. Developments in the automation of accurate in-situ ground-based peat surface motion techniques also mean that high temporal resolution point records from the peatland surface are now possible at relatively low cost [9,10].…”

“…Third, detailed knowledge of the mechanical processes that underpin the variability in peat surface motion belong in a very different academic field to ecology and hydrology and, consequently, knowledge of peat mechanics is underdeveloped relative to other peatland disciplines. Therefore, it is only with the recent moves toward large scale monitoring using InSAR [1,5,7] and LiDAR [26] that there has been an incentive to develop PSM monitoring beyond measures of subsidence.…”