Airborne Hyperspectral Evaluation of Maximum Gross Photosynthesis, Gravimetric Water Content, and CO2 Uptake Efficiency of the Mer Bleue Ombrotrophic Peatland

J Arroyo-Mora,Raymond Soffer,Sari Juutinen,George Leblanc,Tim Moore,Margaret Kalacska,Nigel Roulet,Deep Inamdar,Gabriela Ifimov

doi:10.3390/rs10040565

Abstract

Peatlands cover a large area in Canada and globally (12% and 3% of the landmass, respectively). These ecosystems play an important role in climate regulation through the sequestration of carbon dioxide from, and the release of methane to, the atmosphere. Monitoring approaches, required to understand the response of peatlands to climate change at large spatial scales, are challenged by their unique vegetation characteristics, intrinsic hydrological complexity, and rapid changes over short periods of time (e.g., seasonality). In this study, we demonstrate the use of multitemporal, high spatial resolution (1 m2) hyperspectral airborne imagery (Compact Airborne Spectrographic Imager (CASI) and Shortwave Airborne Spectrographic Imager (SASI) sensors) for assessing maximum instantaneous gross photosynthesis (PGmax) in hummocks, and gravimetric water content (GWC) and carbon uptake efficiency in hollows, at the Mer Bleue ombrotrophic bog. We applied empirical models (i.e., in situ data and spectral indices) and we derived spatial and temporal trends for the aforementioned variables. Our findings revealed the distribution of hummocks (51.2%), hollows (12.7%), and tree cover (33.6%), which is the first high spatial resolution map of this nature at Mer Bleue. For hummocks, we found growing season PGmax values between 8 μmol m−2 s−1 and 12 μmol m−2 s−1 were predominant (86.3% of the total area). For hollows, our results revealed, for the first time, the spatial heterogeneity and seasonal trends for gravimetric water content and carbon uptake efficiency for the whole bog.

Highlights

Peatlands are characterized by the accumulation of large amounts of organic carbon (C), generally from 30 kg C m−2 to >250 kg C m−2 [1]
We demonstrate the use of multitemporal, high spatial resolution (1 m2) hyperspectral airborne imagery (Compact Airborne Spectrographic Imager (CASI) and Shortwave Airborne Spectrographic Imager (SASI) sensors) for assessing maximum instantaneous gross photosynthesis (PGmax) in hummocks, and gravimetric water content (GWC) and carbon uptake efficiency in hollows, at the Mer Bleue ombrotrophic bog
Our results show that values of 8–12 μmol m−2 s−1 are predominant at Mer Bleue during this time, it is important to note that the empirical model relating PGmax and normalized difference vegetation index (NDVI) has a coefficient of determination of 0.6, and our results of PGmax for hummocks are approximate

Summary

Introduction

Peatlands are characterized by the accumulation of large amounts of organic carbon (C), generally from 30 kg C m−2 to >250 kg C m−2 [1]. Hummocks are drier elevated mounds with a denser cover of vascular plants and a thicker acrotelm (aerated layer above the water table) than lower-lying, wetter hollows, which are dominated by mosses (in bogs, generally Sphagnum spp.) [2,3]. These two microforms differ in species composition and rates of processes such as photosynthesis and respiration [3,4]. The vertical microtopographic variation between hummocks and hollows is much less than 1 m [5]

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Results

Discussion

Conclusion