High greenhouse gas fluxes from peatlands under various disturbances in the Peruvian Amazon

Abstract

Abstract. Amazonian peat swamp forests remove large amounts of carbon dioxide (CO2) but anaerobic decomposition of the peat produces methane (CH4). Drought or cultivation cuts down on the CH4 production but may increase the CO2 emission. Varying oxygen content in nitrogen-rich peat produces nitrous oxide (N2O). Despite the potentially tremendous changes, greenhouse gas emissions from peatlands under various land uses and environmental conditions have rarely been compared in the Amazon. We measured CO2, CH4 and N2O emissions from the soil surface with manual opaque chambers, and environmental characteristics in three sites around Iquitos, Peru from September 2019 to March 2020: a pristine peat swamp forest, a young forest and a slash-and-burn manioc field. The manioc field showed moderate peat respiration and N2O emission. The swamp forests under slight water table drawdown emitted large amounts of CO2 and N2O while retaining their high CH4 emissions. Most noticeably, a heavy shower after the water-table drawdown in the pristine swamp forest created a hot moment of N2O. Nitrifier denitrification was the likely source mechanism, as we rule out nitrification and heterotrophic denitrification. We base the judgement on the lack of nitrate and oxygen, and the suppressed denitrification potential in the topsoil. Overall, our study shows that even moderate drying in Peruvian palm swamps may create a devastating feedback on climate change through CO2 and N2O emissions.

Comment on bg-2021-46

“…Hergoualc'h et al (2020) identified nitrifier denitrification in the palm swamp. It is a well-documented process in mineralised peats (Wrage-Mönnig et al, 2018;Masta et al, 2020). Anaerobic NH4 + oxidation (anammox) involves nitric oxide (NO) as an intermediate product which could serve as an important substrate for N2O formation by NH4 + oxidisers or denitrifiers (Hu et al, 2015).…”

“…Across the study period, the fluxes correlated log-linearly with soil NH4 + content (Figure 6a). The DNDC model calculates N2O fluxes driven by decomposition of organic N and denitrification following rainfall events (Li et al, 1992). However, more records of N2O peaks after rainfall events are needed to feed a model properly.…”

“…Most of anaerobic N2O production pathways use NO3as the source (Baggs, 2011;Butterbach-Bahl et al, 2013;Hu et al, 2015). Among the few exceptions, nitrifier denitrification avoids NO3reducing NO2 − straight into N2O (Wrage-Mönnig et al, 2018). Hergoualc'h et al (2020) identified nitrifier denitrification in the palm swamp.…”