Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin

Here we report methane (CH4) and nitrous oxide (N2O) fluxes from lowland tropical peatlands in the Pastaza-Marañón foreland basin (PMFB) in Peru, one of the largest peatland complexes in the Amazon basin. Trace gas fluxes were sampled from the most numerically-dominant peatland vegetation types in the region: forested vegetation, forested (short pole) vegetation, Mauritia flexuosa-dominated palm swamp, and mixed palm swamp. Data were collected in both wet and dry seasons over the course of four field campaigns from 2012 to 2014. Peatlands in the PMFB were large and regionally significant sources of atmospheric CH4, emitting 36.05 ± 3.09 mg CH4-C m−2 d−1. CH4 emissions varied significantly among vegetation types and between seasons. CH4 fluxes were greatest for mixed palm swamp (52.0 ± 16.0 mg CH4-C m−2 d−1), followed by M. flexuosa palm swamp (36.7 ± 3.9 mg CH4-C m−2 d−1), forested (short pole) vegetation (31.6 ± 6.6 mg CH4-C m−2 d−1), and forested vegetation (29.8 ± 10.0 mg CH4-C m−2 d−1). CH4 fluxes also showed marked seasonality, with divergent seasonal flux patterns among ecosystems. Forested vegetation and mixed palm swamp showed significantly higher dry season (47.2 ± 5.4 mg CH4-C m−2 d−1 and 85.5 ± 26.4 mg CH4-C m−2 d−1, respectively) compared to wet season emissions (6.8 ± 1.0 mg CH4-C m−2 d−1 and 5.2 ± 2.7 mg CH4-C m−2 d−1, respectively). In contrast, forested (short pole) vegetation and M. flexuosa palm swamp showed the opposite trend, with dry season fluxes of 9.6 ± 2.6 and 25.5 ± 2.9 mg CH4C m−2 d−1, respectively, versus wet season fluxes of 103.4 ± 13.6 and 53.4 ± 9.8 mg CH4-C m−2 d−1, respectively. Nitrous oxide fluxes were negligible (0.70 ± 0.34 µg N2O-N m−2 d−1), and did not vary significantly among ecosystems or between seasons.