Assessing Drought Resilience of Restored Peatlands Using Combined Optical and Microwave Satellite Data

Background
Peatlands are a key component of the terrestrial carbon cycle. They sequester large amounts of carbon from the atmosphere. Peat-forming plants such as Sphagnum moss are well adapted to this wet environment and suffer in dry conditions. Many peatlands in the British Isles have, however, been subject to deleterious management schemes, including drainage, overgrazing, planting for commercial forestry, and burning. Although large-scale restoration efforts have now been implemented, it is often challenging to completely restore the hydrological characteristics of such sites. This leaves them vulnerable to drought periods, during which markedly negative effects on photosynthesis of peatland vegetation, and ultimately carbon emissions, can be observed. The number of Earth Observation satellites available to study peatlands has risen markedly in the past few years with the advent of the Copernicus Sentinel-1 and Sentinel-2 missions. The Sentinel-1 satellites carry synthetic aperture radar (SAR) instruments which are sensitive to soil and plant moisture and, critically, are not affected by cloud cover which can dominate peatland areas. The Sentinel-2 satellites carry optical instruments that are sensitive to the visible and near infra-red parts of the electromagnetic spectrum. This makes them ideal for monitoring plant health. In future, we will also have direct observations of photosynthesis from the European Space Agency’s “FLEX” Earth Explorer mission (planned launch 2022), which measures Solar Induced Fluorescence (SIF) from plants.

Aims and Objectives
This project aims to examine the resilience of restored and natural peatlands to drought conditions, particularly of different peatland microforms, through the plant photosynthetic response to drought and rewetting. The studentship will investigate various remotely sensed radar and optical signatures of drought responses, develop a novel method utilising SIF, and test the applicability of remotely monitoring peatland resilience on a landscape scale.

Outline Plan for the first 12-18 months
The PhD project will Initiate the following component projects:
1) Laboratory based study of the drying of different peatland microforms on SAR/Sentinel-2 measurements. We will house these experiments on a lysimeter and take regular measurements with a ground-based SAR system configured to match Sentinel-1 measurements. Optical measurements to simulate Sentinel-2 will be taken alongside the SAR observations. Together these will be used to calibrate a joint SAR-optical model of drying and rewetting responses.
2) Field based studies of optical and SIF measurements. The student will conduct a field campaign during year 1-2 to monitor restored and non-restored sites with hand-held optical instruments including a spectro-radiometer (supplied by U. Reading) and a SIF spectrometer (from the NERC Field Spectroscopy Facility). These data, alongside in-situ soil moisture and gross primary production data (JHI long term datasets) will allow us to test models devolved in part (1). The SIF data will be used to explore the additional benefit of missions such as FLEX.
3) Examining the 2018 drought. The Sentinel-1 and 2 data for 2018 will be extracted for the Forsinard flows and the impact of the drought of that year on the peatlands will be explored based on the relationships built in parts (1) and (2). The student will test the resilience of Sphagnum as a key contributor in restored peatlands. These by and large tend to be lawn/hollow species such as S. cuspidatum, S.fallax or S.capillifolium, which are thought to have lower drought tolerance than hummock-forming species. If a drought occurs during the PhD we will use data for that year if feasible.