Hydrometeorological sensitivities of net ecosystem carbon dioxide and methane exchange of an Amazonian palm swamp peatland

Authors: GRIFFIS, TIMOTHY - University Of Minnesota; ROMAN, DANIEL - Us Forest Service (FS); WOOD, JEFFREY - University Of Missouri; DEVENTER, JULIAN - University Of Minnesota; FACHIN, LIZARDO - Research Institute Of The Peruvian Amazon; RENGIFO, JHON - Research Institute Of The Peruvian Amazon; DEL CASTILLO TORRES, DENNIS - Research Institute Of The Peruvian Amazon; LILLESKOV, ERIK - Us Forest Service (FS); KOLKA, RANDALL - Us Forest Service (FS); CHIMNER, RODNEY - Michigan Technological University; DEL AGUILA-PASQUEL, JHON - Research Institute Of The Peruvian Amazon; WAYSON, CRAIG - Us Forest Service (FS); HERGOUALC'H, KRISTELL - Center For International Forestry Research; Baker, John; CADILLO-QUIROZ, HINSBY - Arizona State University; RICCIUTO, DANIEL - Oak Ridge National Laboratory

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2020
Publication Date: 12/15/2020
Citation: Griffis, T.J., Roman, D.T., Wood, J.D., Deventer, J.M., Fachin, L., Rengifo, J., del Castillo Torres, D., Lilleskov, E., Kolka, R.K., Chimner, R.A., del Aguila-Pasquel, J., Wayson, C., Hergoualc'h, K., Baker, J.M., Cadillo-Quiroz, H., Ricciuto, D.M. 2020. Hydrometeorological sensitivities of net ecosystem carbon dioxide and methane exchange of an Amazonian palm swamp peatland. Agricultural and Forest Meteorology. 295. Article 108167. https://doi.org/10.1016/j.agrformet.2020.108167.
DOI: https://doi.org/10.1016/j.agrformet.2020.108167

Interpretive Summary: The role of tropical peatlands in the global greenhouse gas cycle is understudied and not well-understood. These ecosystems occur in lowland areas of Southeast Asia and the Amazon basin in South America, including the Loreto Region in Peru. Little is known about the biogeochemistry of these peatlands, and particularly their impact on CO2 and CH4 exchange, and their response to changes in the hydrologic cycle. To address these issues, we established an instrument tower in a palm swamp forest within a peatland near Iquitos, Peru for the measurement of CO2 and CH4 fluxes by eddy covariance. Measurements were made over a two-year period, and we found that hydrology (wet versus dry seasons) had a strong effect on carbon cycling. Both high temperature and high vapor pressure deficits were critical limiting factors on photosynthesis during the dry season. Cumulative totals over the study period showed that the peatland was a strong sink for CO2 ranging from -420 to -455 gC/m2. The forest was a source for CH4, releasing approximately 27 gC/m2., similar to results from other tropical peatlands. Thus, overall the ecosystem was a major sink for carbon. These results will be useful for the validation of global models of the terrestrial carbon cycle and its impact on climate.

Technical Abstract: Tropical peatlands are a major, but understudied, biophysical feedback factor on the atmospheric greenhouse effect. The largest expanses of tropical peatlands are located in lowland areas of Southeast Asia and the Amazon basin. The Loreto Region of Amazonian Peru contains ~63,000 km2 of peatlands. However, little is known about the biogeochemistry of these peatlands, and in particular, the cycling of carbon dioxide (CO2) and methane (CH4), and their responses to hydrometeorological forcing. To address these knowledge gaps, we established an eddy covariance (EC) flux tower in a palm (Mauritia flexuosa L.f.) swamp peatland near Iquitos, Peru. Here, we report ecosystem-scale CO2 and CH4 flux observations for this Amazonian palm swamp peatland over a two-year period. The seasonal variation in hydrometeorology (wet versus dry seasons) had a strong effect on CO2 and CH4 fluxes. High air temperature and vapor pressure deficit (VPD) exerted an important limitation on photosynthesis during the dry season. Evidence from light- response analyses and flux partitioning support that photosynthetic activity was strongly downregulated during the dry seasons. The cumulative net ecosystem CO2 exchange indicated that the peatland was a significant CO2 sink ranging from -420 (-349 to -543) in 2018 to -455 (-384 to -542) g C m-2 y-1 in 2019. The forest was a CH4 source of 27 (24 to 30) g C m-2 y-1, similar in magnitude to other tropical peatlands and larger than sub-boreal peatlands. Thus, the annual carbon budget of this Amazonian palm swamp peatland appears to be a major carbon sink under current hydrometeorological conditions.