Methane fluxes from seasonally flooded forests in the Amazon basin
Final Report Abstract
The Amazon in South America is largely covered by wetlands and is a key region for tropical CH4 emissions. Despite its importance for the global methane budget, the overall CH4 emission from the Amazon basin is not well quantified and the individual CH4 sources are not well understood. This project proposed to initiate different type of CH4 flux measurements in a typical Amazon ecosystem, so that the ecosystems individual CH4 sources and sinks can be quantified, and the net ecosystem CH4 flux can be determined. The 51m high K34 tower, located at fieldsite ZF2, is located in a typical Terra Firme (upland forest) landscape. A FTIR‐analyzer (which measures CO2, CH4, N2O, CO and δ13CO2) was set up at the tower, and was connected to a REA‐flux system, a methodology which can provide integrated (above‐canopy) ecosystem CH4 fluxes. However, first analyses of the REA‐flux measurements revealed that the CH4 fluxes were too low for the FTIR‐REA set up, probably as a consequence of the high turbulence above the canopy. Nonetheless, by use of tower profile measurements, integrated ecosystem fluxes could still be estimated successfully. Ecosystem CH4, N2O and CO emissions were estimated to be 1.2‐2.0, 0.08‐0.4 and 1.2‐2.0 nmol m^‐2 s^‐1 respectively, thereby being a clear source of all three gas species. The tower concentration measurements also showed the presence of CH4 and CO peaks, passing by the K34 tower, and entering the forest from above. Wind speed and direction analyses indicated that these peaks likely originated from the surrounding valleys. Campaign‐based experiments were set up to study the individual sources and sinks of CH4, for which a Los Gatos‐ analyzer was used. Soil CH4 fluxes were measured along a topographical gradient and, overall, CH4 uptake was observed on the plateau and slopes, while emission was observed in the valleys. The valley stream, rotting dead wood, and especially termite mounds were found to be strong emitters of CH4, acting as CH4 hotspots in the ecosystem, and termite mounds were even estimated to emit 0.5‐1.0 nmol m^‐2 s^‐1 on ecosystem scale, thereby being a significant player in the local CH4 budget. In addition, by use of a small incubation chamber, the termite emission factor for a typical Amazon termite species was determined, only the second termite emission factor presented for the Amazon. The comparison of the integrated ecosystem CH4 estimate with the individual source measurements points at the important role of hotspots in the ecosystems CH4 budget. Soil N2O and CO fluxes were measured in the valley and on the plateau. In addition, nighttime N2O and CO concentrations in the waterlogged valley were monitored. Valley N2O emission were almost negligible, while plateau N2O emissions were small but consistent, and of similar magnitude as estimated by the plateau tower measurements. Soil CO emission were high on the plateau, and even higher in the valley. The measurement of nighttime CO concentrations showed the strong buildup of CO in the valleys, indicating that the CO peaks observed at the K34 tower could indeed originate from these valleys. The CO flux measurements are of importance because, up till now, it was assumed that tropical forest soils mostly act as a CO sink. The combination of flux measurements at different spatial and temporal scales, and of different gas species simultaneously, resulted in a valuable dataset, unique for the Amazonian rainforest.
Publications
- Understanding nighttime methane signals at the Amazon Tall Tower Observatory (ATTO), Atmospheric Chemistry and Physics , 2020
Botía, S., Gerbig, C., Marshall, J., Lavric, J.V., Walter, D., Pöhlker, C., Holanda, B., Fisch, G., de Araújo, A.C., Sá, M.O., Teixeira, P.R., Resende, A.F., Dias‐Junior, C.Q., van Asperen, H., Oliveira, P.S., Stefanello, M., & Acevedo, O.C.
(See online at https://doi.org/10.5194/acp-20-6583-2020) - Biogenic Volatile Organic Compounds (BVOC) decomposing leaf litter in central Amazonia, ATTO project science meeting, online
M.G. Caetano, D. Pinheiro, M. Robin, H van Asperen, N. Martins, C. Hartmann, J. Williams, S. Wolff, S. Trumbore., E Gomes‐Alves
- Diel emissions of Volatile Organic Compound from soil and litter in the central amazon, ATTO project science meeting, online
D. Pinheiro, M.G. Caetano, M. Robin, H van Asperen, S. Wolff, R.A. Souza, S Jones, C.A. Quesada, S. Trumbore, E Gomes‐Alves
- The role of termite CH4 emissions on the ecosystem scale: a case study in the Amazon rainforest, Biogeosciences, 2021
van Asperen, H., Alves‐Oliveira, J.R., Warneke, T., Forsberg, B., de Araújo, A.C., & Notholt, J.
(See online at https://doi.org/10.5194/bg-18-2609-2021) - Tropical forest CH4: from termite mounds to tower measurements, PICO presentation, EGU General Assembly, online, 2021
Hella van Asperen, Thorsten Warneke, Alessandro C De Araújo, Bruce Forsberg, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Marta Sá, Paulo Teixeira, Robson Azevedo de Oliveira, Leila Leal, Veber Moura, João Rafael Alves‐Oliveira, Santiago Botia, Jost Lavrič, Shujiro Komiya, Arnoud Frumau, Arjan Hensen, Danielle van Dinther, Pim van den Bulk, and Justus Notholt
- Tropical forest CH4 budget: the importance of local hotspots, PICO presentation, EGU General Assembly, May 2022
Hella van Asperen, Thorsten Warneke, Alessandro De Araújo, Bruce Forsberg, Sávio Ferreira, João Alves‐Oliveira, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Marta Sá, Paulo Teixeira, Elaine Pires, Veber Moura, Shujiro Komiya, Santiago Botia, Sam Jones, Jost Lavrič, Susan Trumbore, and Justus Notholt
(See online at https://doi.org/10.5194/egusphere-egu22-11693)
