Fig. 4.

RGB image and hyperspectral false-color images showing the peat type and the spatial variability within the peat mesocosms. The false-color image is combined from the three main components of principal component analysis of hyperspectral shortwave infrared (1,000–2,500 nm) imaging. The cores used for hyperspectral imaging (one bare and one vegetated) were not used during the experiment and thus were not subjected to sequential thawing. These unaltered cores were sampled at the same time as the mesocosms used in the experiment, and represent the original peat structure and chemistry under natural conditions. The average length of the cores was 80 cm, the average maximum seasonal thaw depth was 65 cm, and the length of the permafrost part was 15 cm. Owing to the presence of ice lenses in the bare core, the permafrost part was compacted after thawing. The degree of peat humification is indicated on the von Post scale, ranging from H1 (completely undecomposed) to H10 (completely decomposed).