The Flow Country Peatlands of Scotland: Foreword

First paragraph: In the far north of Scotland, a vast and varied expanse of blanket peatland (Figure 1) extends across an area of 4,000 km2 within the historic counties of Caithness and Sutherland, from the foot of the mountains in the west to the coast in the east. It is the largest expanse of blanket mire in Europe (Lindsay et al. 1988) and the largest single terrestrial carbon store in the UK (Chapman et al. 2009). It is known as the Flow Country. The Flow Country has high conservation value, being of particular importance for its suite of breeding birds which includes the Common Scoter (Melanitta nigra), Greenshank (Tringa nebularia), Dunlin (Calidris alpina), Golden Plover (Pluvialis apricaria) and Hen Harrier (Circus cyaneus), and a refuge for many species normally found closer to the Arctic (Lindsay et al. 1988). The nature conservation importance of this area is reflected in the designation of over 1,300 km2 as Natura 2000 sites under the European Habitats and Birds Directives, including the largest terrestrial Special Area of Conservation (SAC) in the UK, and the current consideration of the Flow Country for World Heritage Site status

Long-term peatland condition assessment via surface motion monitoring using the ISBAS DInSAR technique over the Flow Country, Scotland

Satellite Earth Observation (EO) is often used as a cost-effective method to report on the condition of remote and inaccessible peatland areas. Current EO techniques are primarily limited to reporting on the vegetation classes and properties of the immediate peat surface using optical data, which can be used to infer peatland condition. Another useful indicator of peatland condition is that of surface motion, which has the potential to report on mass accumulation and loss of peat. Interferometic SAR (InSAR) techniques can provide this using data from space. However, the most common InSAR techniques for information extraction, such as Persistent Scatterers’ Interferometry (PSI), have seen limited application over peat as they are primarily tuned to work in areas of high coherence (i.e., on hard, non-vegetated surfaces only). A new InSAR technique, called the Intermittent Small BAseline Subset (ISBAS) method, has been recently developed to provide measurements over vegetated areas from SAR data acquired by satellite sensors. This paper examines the feasibility of the ISBAS technique for monitoring long-term surface motion over peatland areas of the Flow Country, in the northeast of Scotland. In particular, the surface motions estimated are compared with ground data over a small forested area (namely the Bad a Cheo forest Reserve). Two sets of satellite SAR data are used: ERS C-band images, covering the period 1992–2000, and Sentinel-1 C-band images, covering the period 2015–2016. We show that the ISBAS measurements are able to identify surface motion over peatland areas, where subsidence is a consequence of known land cover/land use. In particular, the ISBAS products agree with the trend of surface motion, but there are uncertainties with their magnitude and direction (vertical). It is concluded that there is a potential for the ISBAS method to be able to report on trends in subsidence and uplift over peatland areas, and this paper suggests avenues for further investigation, but this requires a well-resourced validation campaign

An incubation study of GHG flux responses to a changing water table linked to biochemical parameters across a peatland restoration chronosequence

Large areas of northern peatlands have been drained and afforested with conifers in the 20th century. This has led to changes in the hydrology of the peatlands, the quality and quantity of organic matter inputs and soil microbial communities, which are all likely to impact on greenhouse gas (GHG) fluxes. Considerable areas of these forest plantations are undergoing restoration, and our aim was to assess whether contrasting compositions of peat, in conjunction with hydrological changes in a controlled lab experiment, impact on GHG fluxes. We incubated vegetation free cores (at 8 °C) from a near-natural bog, restoration sites felled in 1998, 2006, 2012 and a current forest plantation at (a) low water tables, (b) high tables or (c) water tables that were changed from low to high. Results show that peat quality and nutrient availability in the pore water have been altered by the forest plantations, which resulted in dissimilar carbon dioxide (CO2) fluxes between the sites under the same temperature and water table conditions. Higher CO2 fluxes were found in the peat cores from the forest plantations than from sites that have undergone restoration and from the near-natural bog. However, there were few differences in methane (CH4) fluxes from the different sites, indicating that on its own (i.e., in the absence of biotic interactions under field conditions) the effects of forestry on CH4 flux are limited

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

Peatland 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 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 Aug‐Nov and April‐June respectively. Drier and partially drained sites dominated by shrubs display long‐term subsidence with maximum uplift and subsidence in July‐Oct and Feb‐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 non‐vascular 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

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

Better tools for rapid and reliable assessment of global peatland extent and condition are urgently needed to support action to prevent further decline of peatlands. 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 satellite interferometric synthetic aperture radar (InSAR) to map peatland condition in a blanket bog landscape. We show that the timing of maximum seasonal swelling of the peat is characterised by a bimodal distribution. The first maximum, usually in autumn, is typical of "stiffer"peat associated with steeper topographic gradients, peatland margins, and degraded peatland and more often associated with "shrub"-dominated vegetation communities. The second maximum, usually in winter, is typically associated with "softer"peat typically found in low topographic gradients often featuring pool systems and Sphagnum-dominated vegetation communities. Specific conditions of "soft"and "stiff"peats are also determined by the amplitude of swelling and multi-annual average 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 the 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