Seasonal variability in methane and nitrous oxide fluxes from tropical peatlands in the western Amazon basin
The Amazon plays a critical role in global atmospheric budgets of methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O). However, while we have a relatively good understanding of the continental-scale flux of these greenhouse gases (GHGs), one of the key gaps in know...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-08-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3669/2017/bg-14-3669-2017.pdf |
| Summary: | The Amazon plays a critical role in global atmospheric budgets of
methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O). However, while we have a
relatively good understanding of the continental-scale flux of these
greenhouse gases (GHGs), one of the key gaps in knowledge is the specific
contribution of peatland ecosystems to the regional budgets of these GHGs.
Here we report CH<sub>4</sub> and N<sub>2</sub>O fluxes from lowland tropical peatlands
in the Pastaza–Marañón foreland basin (PMFB) in Peru, one of the
largest peatland complexes in the Amazon basin. The goal of this research was
to quantify the range and magnitude of CH<sub>4</sub> and N<sub>2</sub>O fluxes from
this region, assess seasonal trends in trace gas exchange, and determine the
role of different environmental variables in driving GHG flux. Trace gas
fluxes were determined from the most numerically dominant peatland vegetation
types in the region: forested vegetation, forested (short pole) vegetation,
<i>Mauritia flexuosa</i>-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. Diffusive CH<sub>4</sub> emissions averaged
36.05 ± 3.09 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup> across the entire dataset,
with diffusive CH<sub>4</sub> flux varying significantly among vegetation
types and between seasons. Net ebullition of CH<sub>4</sub> averaged
973.3 ± 161.4 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup> and did not vary significantly among
vegetation types or between seasons. Diffusive CH<sub>4</sub> flux was greatest
for mixed palm swamp (52.0 ± 16.0 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>),
followed by <i>M. flexuosa</i> palm swamp (36.7 ± 3.9 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>), forested (short pole) vegetation
(31.6 ± 6.6 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>), and forested vegetation
(29.8 ± 10.0 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>). Diffusive CH<sub>4</sub> flux also
showed marked seasonality, with divergent seasonal patterns among ecosystems.
Forested vegetation and mixed palm swamp showed significantly higher dry
season (47.2 ± 5.4 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup> and
85.5 ± 26.4 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>, respectively) compared to wet season
emissions (6.8 ± 1.0 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup> and
5.2 ± 2.7 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>, respectively). In contrast, forested
(short pole) vegetation and <i>M. flexuosa</i> palm swamp showed the
opposite trend, with dry season flux of 9.6 ± 2.6 and
25.5 ± 2.9 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>, respectively, versus wet season flux of
103.4 ± 13.6 and 53.4 ± 9.8 mg CH<sub>4</sub>–C m<sup>−2</sup> day<sup>−1</sup>,
respectively. These divergent seasonal trends may be linked to very high
water tables (> 1 m) in forested vegetation and mixed palm swamp
during the wet season, which may have constrained CH<sub>4</sub> transport across
the soil–atmosphere interface. Diffusive N<sub>2</sub>O flux was very low
(0.70 ± 0.34 µg N<sub>2</sub>O–N m<sup>−2</sup> day<sup>−1</sup>) and did not vary
significantly among ecosystems or between seasons. We conclude that
peatlands in the PMFB are large and regionally significant sources of
atmospheric CH<sub>4</sub> that need to be better accounted for in regional
emissions inventories. In contrast, N<sub>2</sub>O flux was negligible, suggesting
that this region does not make a significant contribution to regional
atmospheric budgets of N<sub>2</sub>O. The divergent seasonal pattern in CH<sub>4</sub>
flux among vegetation types challenges our underlying assumptions of the
controls on CH<sub>4</sub> flux in tropical peatlands and emphasizes the need for
more process-based measurements during periods of high water table.</p> |
|---|---|
| ISSN: | 1726-4170 1726-4189 |