Use of Surface Motion Characteristics Determined by InSAR to Assess Peatland Condition

Lubna Alshammari,David J. Large,Andrew Sowter,Chris Marshall,Stuart Marsh,Roxane Andersen,Peter Gilbert,Doreen S. Boyd

doi:10.1029/2018jg004953

Abstract

AbstractPeatland surface motion is a key property of peatland that relates to condition. However, field‐based techniques to measure surface motion are not cost‐effective over large areas and long time periods. An alternative method that can quantify peatland surface motion over large areas is interferometric synthetic aperture radar. Although field validation of the accuracy of this method is difficult, the value of interferometric synthetic aperture radar (InSAR) as a means of quantifying peat condition can be tested. To achieve this, the characteristics of InSAR time series measured over an18‐month period at 22 peatland sites in the Flow Country northern Scotland were compared to site condition assessment based on plant functional type and site management history. Sites in good condition dominated by Sphagnum display long‐term stability or growth and a seasonal cycle with maximum uplift and subsidence in August–November and April–June, respectively. Drier and partially drained sites dominated by shrubs display long‐term subsidence with maximum uplift and subsidence in July–October and February–June, respectively. Heavily degraded sites with large bare peat extent display subsidence with no distinct seasonal oscillations. Seasonal oscillation in surface motion at sites with a dominant nonvascular plant community is interpreted as resulting from changes in seasonal evaporative demand. On sites with extensive vascular plants cover and falling water table, surface oscillations are interpreted as representing sustained drawdown during the growing season and subsequent recharge in late winter. This study highlights the potential to use InSAR to characterize peatland condition and provide a new view of the surface dynamics of peatland landscapes.

Highlights

Peatland surfaces are dynamic (Ingram, 1983) and move in response to changes in the mass of water, gas, and organic matter stored within the peat body
Based on the similarity of the trends extracted using singular spectrum analysis, the interferometric synthetic aperture radar (InSAR) time series of surface motion for each of the 22 study sites were seen to group into four categories labeled Categories A to D (Figure 6)
The interpretation presented carries important implications: Surface motion attributed to changes in water budget, water table depth, and energy balance are linked to carbon balance and net ecosystem exchange (Laine et al, 2007; Mezbahuddin et al, 2017; Moore et al, 1998)

Summary

Introduction

Peatland surfaces are dynamic (Ingram, 1983) and move in response to changes in the mass of water, gas, and organic matter stored within the peat body. Large contributing factors (Fritz et al, 2008; Kennedy & Price, 2005): growth because of accumulation; irreversible subsidence caused by drainage, compression, and decay of organic matter; and reversible elastic deformation of the peat matrix due to seasonal and shorter‐term variation in the mass of water and gas stored within the peat. Each of these contributing factors relates to peat condition, and this in turn relates to ecosystem services provided by peatlands (Glenk et al, 2014). Long‐term peat growth is indicative of carbon sequestration and good condition; long‐term subsidence is indicative of carbon loss and poor condition; and reversible seasonal deformation is sensitive to the elastic properties of the peat matrix which are in turn sensitive to degradation (Kennedy & Price, 2005)

Methods

Results

Discussion

Conclusion