Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw

Abstract

Permafrost in the Arctic is thawing, exposing large carbon and nitrogen stocks for decomposition. Gaseous carbon release from Arctic soils due to permafrost thawing is known to be substantial, but growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N 2 O). Here we show that N 2 O emissions from subarctic peatlands increase as the permafrost thaws. In our study, the highest postthaw emissions occurred from bare peat surfaces, a typical landform in permafrost peatlands, where permafrost thaw caused a fivefold increase in emissions (0.56 ± 0.11 vs. 2.81 ± 0.6 mg N 2 O m −2 d −1 ). These emission rates match those from tropical forest soils, the world's largest natural terrestrial N 2 O source. The presence of vegetation, known to limit N 2 O emissions in tundra, did decrease (by ∼90%) but did not prevent thaw-induced N 2 O release, whereas waterlogged conditions suppressed the emissions. We show that regions with high probability for N 2 O emissions cover one-fourth of the Arctic. Our results imply that the Arctic N 2 O budget will depend strongly on moisture changes, and that a gradual deepening of the active layer will create a strong noncarbon climate change feedback.

Riparian Corridors: A New Conceptual Framework for Assessing Nitrogen Buffering Across Biomes

“…Furthermore, headwater aquatic primary production (algae) is often phosphorus limited, resulting in rapid nitrification of what little ammonium makes it to the stream channel, though nitrogen demand increases as rivers meet the sea McClelland et al, 2012). There is evidence that rapid climate change at high latitudes and associated permafrost degradation are increasing nitrogen availability and potentially induce shifts in the nitrogen cycle (Jones et al, 2005;Abbott et al, 2015;Voigt et al, 2017). Particularly, increased nutrient delivery to riparian zones and stream networks from degrading permafrost could enhance or suppress nitrogen uptake depending on the nutrient stoichiometry.…”

Ecosystem carbon response of an Arctic peatland to simulated permafrost thaw

“…We collected 16 intact peat mesocosms ( Ø = 10 cm, length ~80 cm) from vegetated (eight mesocosms with typical, low‐statured palsa vegetation) and naturally bare (eight mesocosms without vascular plants and only covered sporadically with lichens) parts of the palsa complex, using a custom‐made steel corer (Figure S1) (Voigt, Marushchak et al, ). Due to the comparatively small surface area, and to minimize root damage during sampling, patches with larger vascular plants such as B. nana L. were not included for mesocosm collection.…”

“…The vegetation and moisture scenarios used in this study are referred to as DB (dry, bare), DV (dry, vegetated), WB (wet, bare), and WV (wet, vegetated). Step‐wise thawing was achieved by placing the mesocosms in a saltwater‐filled and glycol‐circulated bath at temperatures below 0°C, as described earlier (Voigt, Marushchak et al, ). In short, we sequentially unfroze the mesocosms from top to bottom in 5–20 cm increments during six thawing stages, each lasting four weeks (Table S1).…”

“…Soil gas sampling and analysis were described in detail by Voigt, Lamprecht et al (), Voigt, Marushchak et al (). Briefly, soil gas sampling followed two different methods depending on whether the sample was taken below or above the water table level.…”

“…Water samplers were installed in three depths in each mesocosm: 5–10 cm and 35–40 cm below the soil surface (in the active layer) and 0–5 cm below the maximum seasonal thaw depth (~65–70 cm below the soil surface). Pre‐evacuated 12 ml screw‐cap vials (Labco Exetainer®) connected to the Rhizon tubes were used to sample pore water (Voigt, Marushchak et al, ). Pore water samples were frozen until further analysis and amounts of DOC in the pore water were determined as described by Voigt, Lamprecht et al ().…”