Belowground in situ redox dynamics and methanogenesis recovery in a degraded fen during dry-wet cycles and flooding

Abstract

Climate change induced drying and flooding may alter the redox conditions of organic matter decomposition in peat soils. The seasonal and intermittent changes in pore water solutes (NO<sub>3</sub><sup>−</sup>, Fe<sup>2+</sup>, SO<sub>4</sub><sup>2−</sup>, H<sub>2</sub>S, acetate) and dissolved soil gases (CO<sub>2</sub>, O<sub>2</sub>, CH<sub>4</sub>, H<sub>2</sub>) under natural water table fluctuations were compared to the response under a reinforced drying and flooding in fen peats. Oxygen penetration during dryings led to CO<sub>2</sub> and CH<sub>4</sub> degassing and to a regeneration of dissolved electron acceptors (NO<sub>3</sub><sup>−</sup>, Fe<sup>3+</sup> and SO<sub>4</sub><sup>2−</sup>). Drying intensity controlled the extent of the electron acceptor regeneration. Iron was rapidly reduced and sulfate pools ~ 1 mmol L<sup>−1</sup> depleted upon rewetting and CH<sub>4</sub> did not substantially accumulate until sulfate levels declined to ~ 100 μmoll<sup>−1</sup>. The post-rewetting recovery of soil methane concentrations to levels ~ 80 μmoll<sup>−1</sup> needed 40–50 days after natural drought. This recovery was prolonged after experimentally reinforced drought. A greater regeneration of electron acceptors during drying was not related to prolonged methanogenesis suppression after rewetting. Peat compaction, solid phase content of reactive iron and total reduced inorganic sulfur and organic matter content controlled oxygen penetration, the regeneration of electron acceptors and the recovery of CH<sub>4</sub> production, respectively. Methane production was maintained despite moderate water table decline of 20 cm in denser peats. Flooding led to accumulation of acetate and H<sub>2</sub>, promoted CH<sub>4</sub> production and strengthened the co-occurrence of iron and sulfate reduction and methanogenesis. Mass balances during drying and flooding indicated that an important fraction of the electron flow must have been used for the generation and consumption of electron acceptors in the solid phase or other mechanisms. In contrast to flooding, dry-wet cycles negatively affect methane production on a seasonal scale but this impact might strongly depend on drying intensity and on the peat matrix, whose structure and physical properties influence moisture content

Legacy effects of drought alters the aquatic food web of a northern boreal peatland

“…As temporary aquatic ecosystems, peatlands are sensitive to changes in the frequency and duration of inundation. Yet, we know relatively Knorr, & Blodau, 2013). In contrast to the response following antecedent drought, there was no increase in nutrient levels following the spring thaw in 2014, which was preceded by a growing season with constant inundation (i.e.…”

Effects of water-saving irrigation practices and drought resistant rice variety on greenhouse gas emissions from a no-till paddy in the central lowlands of China

“…2a and b. In contrast to flooding, dry-wet cycles negatively affect methane production (Estop-Aragonés et al, 2013) by preventing the development of soil reductive conditions (Minamikawa and Sakai, 2006). As shown in Fig.…”

“…The dry-wet cycles of the FWI and FDI treatments might alter the availability of alternative electron acceptors during the process of CH 4 production. Oxygen penetration during drying led to CO 2 and CH 4 degassing and a regeneration of dissolved electron acceptors (NO 3 − , Fe 3+ and SO 4 2-) (Estop-Aragonés et al, 2013), which might consume H 2 to weaken the reduction of CO 2 or acetate for CH 4 production (Jain et al, 2004). The drying intensity controlled the extent of the electron acceptor regeneration and might result in different CH 4 emissions between FWI and FDI treatments ( Fig.…”

Effects of extreme experimental drought and rewetting on CO2 and CH4 exchange in mesocosms of 14 European peatlands with different nitrogen and sulfur deposition

“…Raised sulfur (S) deposition in peatlands may favor sulfate reduction against methanogenesis and thus potentially lower CH 4 emissions, which has been demonstrated in many studies (Shannon & White, 1996;Gauci et al, 2004a;Dowrick et al, 2006), although occasionally only effects on sulfate and sulfur pool sizes were found (Vile et al, 2003). The impact of elevated sulfur levels in peats on methanogenesis becomes particularly important during and after dry periods when sulfate is generated and, upon rewetting, temporarily suppresses methanogenesis until being largely exhausted (Shannon & White, 1996;Estop-Aragon es et al, 2013). For a given period of dryness, it can be expected that larger sulfate pools are generated in sulfur-rich peatlands and that methanogenesis and CH 4 emissions are suppressed for longer periods of time.…”