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.
Highlights
Peatlands are an enormous sink of carbon and nitrogen (IPCC, 2019)
The threat is acute in tropical peatlands (IPCC, 2019)
The principal component analysis (PCA) clearly separated our three sites along a water table gradient closely followed by soil O2 content, soil temperature and NO3– content gradients (Figure 2)
Summary
Peatlands are an enormous sink of carbon and nitrogen (IPCC, 2019). Natural and human disturbances may release them as greenhouse gases (GHG). The threat is acute in tropical peatlands (IPCC, 2019). Amazonian swamp forests hold almost a half of tropical peatlands globally (Leifeld and Menichetti, 2018). Most of them are isolated from major population centres and roads, and inaccessible to logging and agriculture Peruvian Amazon Research Institute (IIAP), Iquitos, Peru. Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
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