The carbon (C) budgets of riparian forests are sensitive to climatic variability. Therefore, riparian forests are hot spots of C cycling in landscapes. Only a limited number of studies on continuous measurements of methane (CH4) fluxes from riparian forests is available. Here, we report continuous high-frequency soil and ecosystem (eddy-covariance; EC) measurements of CH4 fluxes with a quantum cascade laser absorption spectrometer for a 2.5-year period and measurements of CH4 fluxes from tree stems using manual chambers for a 1.5 year period from a temperate riparian Alnus incana forest. The results demonstrate that the riparian forest is a minor net annual sink of CH4 consuming 0.24 kg CH4-C ha−1 y−1. Soil water content is the most important determinant of soil, stem, and EC fluxes, followed by soil temperature. There were significant differences in CH4 fluxes between the wet and dry periods. During the wet period, 83% of CH4 was emitted from the tree stems while the ecosystem-level emission was equal to the sum of soil and stem emissions. During the dry period, CH4 was substantially consumed in the soil whereas stem emissions were very low. A significant difference between the EC fluxes and the sum of soil and stem fluxes during the dry period is most likely caused by emission from the canopy whereas at the ecosystem level the forest was a clear CH4 sink. Our results together with past measurements of CH4 fluxes in other riparian forests suggest that temperate riparian forests can be long-term CH4 sinks.
Bibliographical noteFunding Information:
This study was supported by the Ministry of Education and Science of Estonia ( SF0180127s08 grant), the Estonian Research Council ( IUT2-16 , PRG-352 , and MOBERC20 ), the Czech Science Foundation ( 17-18112Y ), SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797 ), the Ministry of Education, Youth and Sports of Czech Republic within the National Sustainability Program I (NPU I, grant number LO1415 ), the EU through the European Regional Development Fund (ENVIRON and EcolChange Centres of Excellence, Estonia, and MOBTP101 returning researcher grant by the Mobilitas Pluss programme), the European Social Fund (Doctoral School of Earth Sciences and Ecology). This work was also supported by Academy of Finland ( 294088 , 288494 ), from the European Research Council (ERC) under the European Union‘s Horizon 2020 research and innovation programme under grant agreement No [ 757695 ], and a Department of Energy (DOE) grant to JPM ( DE-SC0008165 ).
Data Availability StatementSupplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2021.151723.
- Automated chambers
- Eddy covariance
- Quantum cascade laser absorption spectrometer
- Soil fluxes
- Soil water content
- Stem fluxes
- Carbon Dioxide/analysis