Estimating methane emissions using vegetation mapping in the taiga–tundra boundary of a north-eastern Siberian lowland

Abstract

Taiga-tundra boundary ecosystems are affected by climate change. Methane (CH 4) emissions in taiga-tundra boundary ecosystems have sparsely been evaluated from local to regional scales. We linked in situ CH 4 fluxes (2009-2016) with vegetation cover, and scaled these findings to estimate CH 4 emissions at a local scale (10 Â 10 km) using high-resolution satellite images in an ecosystem on permafrost (Indigirka lowland, northeastern Siberia). We defined nine vegetation classes, containing 71 species, of which 16 were dominant. Distribution patterns were affected by microtopographic height, thaw depth and soil moisture. The Indigirka lowland was covered by willow-dominated dense shrubland and cotton-sedge-dominated wetlands with sparse larch forests. In situ CH 4 emissions were high in wetlands. Lakes and rivers were CH 4 sources, while forest floors were mostly neutral in terms of CH 4 emission. Estimated local CH 4 emissions (37 mg m À2 d À1) were higher than those reported in similar studies. Our results indicate that: (i) sedge and emergent wetland ecosystems act as hot spots for CH 4 emissions, and (ii) sparse tree coverage does not regulate local CH 4 emissions and balance. Thus, larch growth and distribution, which are expected to change with climate, do not contribute to decreasing local CH 4 emissions.

Isotopic compositions of ground ice in near-surface permafrost in relation to vegetation and microtopography at the Taiga–Tundra boundary in the Indigirka River lowlands, northeastern Siberia

“…A similar tendency was observed at sites A, B, and V. The mean thaw depths of the tree mounds and wet areas were 19.9±3.3 cm and 30.3±6.7 cm, respectively, for all observation sites (Table 2). The soil moisture of the thaw layer in wet areas (around 50% in volumetric water content) was generally higher than that in tree mounds (around 20% or less in volumetric water content) [64–66].…”

“…On the other hand, the soil moisture in the thaw layer at tree mounds was smaller than that at wet areas [64, 66]. The vegetation of the higher elevation areas (tree mound) was larch trees and shrubs with green-moss and cowberry, whereas that of the lower elevation areas (wet area) was mainly sedges and sphagnum-moss.…”

“…As described previously, pattern (ii) was observed in tree mounds. A higher surface elevation due to frost heave and the accumulation of organic matter or natural levees of former river channels [66, 69] caused the low soil moisture condition. The lower thermal conductivity with the low soil moisture may have induced further ice segregation with slow freezing, as explained in the next section.…”

“…angustifolium ). The transitional area between tree mounds and wet areas contained shrubs with sphagnum-mosses and was labeled as “intermediate areas.” Detailed data were obtained on the vegetation, which as classified into several classes (including tree, shrub, willow, cotton-sedge, and Sphagnum ) based on plant species identified by Morozumi et al [66]. In this study, the tree, shrub, and willow classes were grouped into tree mounds, and the cotton-sedge and Sphagnum classes were grouped into wet areas.…”

An extreme flood caused by a heavy snowfall over the Indigirka River basin in Northeastern Siberia

“…It has been also observed that the excessively wet soil significantly reduces the forest productivity in many locations of the Arctic forest tundra ecosystem (Tei et al, ; Tei & Sugimoto, ). The levels of both carbon dioxide and methane emissions varied at different soil moisture conditions (Shingubara et al, ) and were substantially affected by the flood event (Morozumi et al, ) that occurred in the lower reach of the Indigirka River lowland. Therefore, the flooding can significantly influence the material cycling in the forest tundra over the lowland.…”