Patterns and drivers of organic matter decomposition in peatland open-water pools

Arsenault, Julien; Talbot, Julie; Moore, Tim R.; Knorr, Klaus-Holger; Teickner, Henning; Lapierre, Jean-François

Peatlands pools are unvegetated, inundated depressions that cover up to 30 % of the surface of many temperate and boreal peatlands and that are net carbon (C) sources within C-accumulating ecosystems. The emission of carbon dioxide (CO 2) and methane (CH 4) from peatland pools comes from the degradation of organic matter (OM) that comprise the surrounding matrix. It is, however, not clear how decomposition rates in pools, which define their function and distinguish them from other aquatic ecosystems, vary spatially and what mechanisms drive these variations. We quantified rates of OM decomposition from fresh litter at different depths in six pools of distinct morphological characteristics in a temperate ombrotrophic peatland using litterbags of Sphagnum capillifolium and Typha latifolia over a 27-month period and measured potential CO 2 and CH 4 production of pool sediments in laboratory incubations. Rates of decomposition were faster for T. latifolia than S. capillifolium and, overall, faster at the pool surface and decreased with increasing depth. Pool sediment chemistry was variable among pools and drove the production of CH 4 and CO 2 from sediments, with decreasing CO 2 production with increasing OM humification and decreasing CH 4 production with increasing nitrogen-to-phosphorus ratio. Both CH 4 and CO 2 production from pool sediments were higher in the 1 m deep pools, but similar in the shallow < 1 m and the > 1.5 m deep pools. Our results show that OM decomposition in peatland pools is highly variable and related to OM chemistry, but decomposition depends primarily on the environmental conditions in which it occurs, with differences in both fresh litter and pool sediment decomposability as a function of decreasing O 2 concentrations, light, and temperature with increasing depth in the pools.

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Arsenault, Julien / Talbot, Julie / Moore, Tim R. / et al: Patterns and drivers of organic matter decomposition in peatland open-water pools. 2024. Copernicus Publications.

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