Impacts of Active Versus Passive Re‐Wetting on the Carbon Balance of a Previously Drained Bog

Abstract

AbstractPeatland drainage depletes large carbon stocks by increasing carbon dioxide (CO2) emissions from the soil. Restoration via re‐wetting could play an important role in climate change mitigation, reducing CO2 emissions and increasing C storage within peatlands. However, re‐wetting leads to a biogeochemical compromise between increased CO2 uptake, and enhanced methane (CH4) release. The extent of this compromise in re‐wetted ecosystems with differing environmental conditions is uncertain. To assess re‐wetting effects, we analyzed eddy‐covariance flux measurements from a temperate bog near Vancouver, Canada, from two sites that have undergone different restoration techniques. By the end of the 1‐year study period, the actively re‐wetted, wetter site, was a weak CO2 sink (−26.1 ± 6.1 g C‐CO2 m−2), and the passively re‐wetted, drier site, was near CO2 neutral (3.8 ± 3.1 g C‐CO2 m−2). Higher CH4 emissions at the wetter site led to a larger radiative balance on 20‐ and 100‐year time horizons, implying that the strong radiative effect of CH4 can offset CO2 sink strength on shorter to medium timeframes. However, long‐term radiative forcing (RF) modeling suggests sustained CO2 uptake by the wetter site will eventually lead to a cooling effect on the climate. Furthermore, modeling results emphasize that despite both re‐wetted peatland sites having a positive RF over century timescales, the lack of restoration would have resulted in a significantly larger RF beyond the first few decades following restoration. Results highlight the importance of actively re‐wetting disturbed peatlands to mitigate climate warming and can be used to inform management decisions.