Emerging forest-peatland bistability and resilience of European peatland carbon stores.

Northern peatlands store large amounts of carbon. Observations indicate that forests and peatlands in northern biomes can be alternative stable states for a range of landscape settings. Climatic and hydrological changes may reduce the resilience of peatlands and forests, induce persistent shifts between these states, and release the carbon stored in peatlands. Here, we present a dynamic simulation model constrained and validated by a wide set of observations to quantify how feedbacks in water and carbon cycling control resilience of both peatlands and forests in northern landscapes. Our results show that 34% of Europe (area) has a climate that can currently sustain existing rainwater-fed peatlands (raised bogs). However, raised bog initiation and restoration by water conservation measures after the original peat soil has disappeared is only possible in 10% of Europe where the climate allows raised bogs to initiate and outcompete forests. Moreover, in another 10% of Europe, existing raised bogs (concerning ∼20% of the European raised bogs) are already affected by ongoing climate change. Here, forests may overgrow peatlands, which could potentially release in the order of 4% (∼24 Pg carbon) of the European soil organic carbon pool. Our study demonstrates quantitatively that preserving and restoring peatlands requires looking beyond peatland-specific processes and taking into account wider landscape-scale feedbacks with forest ecosystems.

Characterizing geochemical reactions in unsaturated mine waste-rock piles using gaseous O2, CO2, 12CO2, and 13CO2.

In situ determinations of geochemical reaction rates in mine waste-rock piles remain a challenge. Depth-profiles of field O2 and CO2 pore-gas concentrations, delta13C(CO2) values, and moisture contents were used to characterize and quantify geochemical reaction rates in two waste-rock piles at the Key Lake Uranium Mine in northern Saskatchewan, Canada. Traditionally, the presence of O2 concentrations less than atmospheric in waste-rock piles has been attributed to mineral oxidation. This study showed that the interpretation of O2 and CO2 concentration profiles alone could not be used to identify the depths of dominant geochemical reactions in the piles and could lead to erroneous estimates of reaction rates. Modeling of the delta13C(CO2) depth profiles clearly showed that the gas concentration profiles present in the piles were the result of the oxidation of organic matter present below the piles, a mechanism not previously reported in the literature. Based on these findings, the rates of reactions in the organic zone were determined. The oxidation of organic matter at the base of waste-rock piles should be considered in future mine-waste pore-gas studies, in addition to sulfide oxidation and carbonate buffering.