Assessing the reliability of peatland GPP measurements by remote sensing: From plot to landscape scale

Kirsten J Lees; Myroslava Khomik; Tristan Quaife; Joanna M Clark; Tim Hill; Daniela Klein; Jonathan Ritson; Rebekka R E Artz

doi:10.1016/j.scitotenv.2020.142613

Assessing the reliability of peatland GPP measurements by remote sensing: From plot to landscape scale

Sci Total Environ. 2021 Apr 20:766:142613. doi: 10.1016/j.scitotenv.2020.142613. Epub 2020 Oct 1.

Authors

Kirsten J Lees¹, Myroslava Khomik², Tristan Quaife³, Joanna M Clark⁴, Tim Hill⁵, Daniela Klein⁶, Jonathan Ritson⁷, Rebekka R E Artz⁸

Affiliations

¹ Department of Geography and Environmental Science, University of Reading, Whiteknights, RG6 6DW, UK; Department of Geography, University of Exeter, Streatham Campus, Exeter EX4 4QE, UK. Electronic address: K.lees@exeter.ac.uk.
² University of Waterloo, ON N2L 3G1, Canada.
³ National Centre for Earth Observation, Department of Meteorology, University of Reading, Reading, Whiteknights, RG6 6BB, UK.
⁴ Department of Geography and Environmental Science, University of Reading, Whiteknights, RG6 6DW, UK.
⁵ Department of Geography, University of Exeter, Streatham Campus, Exeter EX4 4QE, UK.
⁶ Forsinard Flows RSPB Office, Forsinard KW13 6YT, UK.
⁷ Imperial College London, SW7 2A7, UK.
⁸ The James Hutton Institute, Craigiebuckler, Aberdeen AB15 8QH, UK.

PMID: 33097258
DOI: 10.1016/j.scitotenv.2020.142613

Abstract

Estimates of peatland carbon fluxes based on remote sensing data are a useful addition to monitoring methods in these remote and precious ecosystems, but there are questions as to whether large-scale estimates are reliable given the small-scale heterogeneity of many peatlands. Our objective was to consider the reliability of models based on Earth Observations for estimating ecosystem photosynthesis at different scales using the Forsinard Flows RSPB reserve in Northern Scotland as our study site. Three sites across the reserve were monitored during the growing season of 2017. One site is near-natural blanket bog, and the other two are at different stages of the restoration process after removal of commercial conifer forestry. At each site we measured small (flux chamber) and landscape scale (eddy covariance) CO₂ fluxes, small scale spectral data using a handheld spectrometer, and obtained corresponding satellite data from MODIS. The variables influencing GPP at small scale, including microforms and dominant vegetation species, were assessed using exploratory factor analysis. A GPP model using land surface temperature and a measure of greenness from remote sensing data was tested and compared to chamber and eddy covariance CO₂ fluxes; this model returned good results at all scales (Pearson's correlations of 0.57 to 0.71 at small scale, 0.76 to 0.86 at large scale). We found that the effect of microtopography on GPP fluxes at the study sites was spatially and temporally inconsistent, although connected to water content and vegetation species. The GPP fluxes measured using EC were larger than those using chambers at all sites, and the reliability of the TG model at different scales was dependent on the measurement methods used for calibration and validation. This suggests that GPP measurements from remote sensing are robust at all scales, but that the methods used for calibration and validation will impact accuracy.

Keywords: Blanket bog; NDVI; Photosynthesis; Satellite; TG model.