TY - JOUR
T1 - Identifying scale-emergent, nonlinear, asynchronous processes of wetland methane exchange
AU - Sturtevant, Cove
AU - Ruddell, Benjamin L.
AU - Knox, Sara Helen
AU - Verfaillie, Joseph
AU - Matthes, Jaclyn Hatala
AU - Oikawa, Patricia Y.
AU - Baldocchi, Dennis
N1 - Funding Information:
Data from US-Myb and US-Tw1 used in this study are freely available from Ameriflux (http://ameriflux.lbl.gov/). The ProcessNetwork software can be downloaded from the MATLAB Central File Exchange (http://www.mathworks.- com/matlabcentral/fileexchange/ 41515-processnetwork-version-1-5-software). We thank Bryan Brock and the California Department of Water Resources for project funding (contract 4600008849). Additional funding was provided by the United States Department of Agriculture (NIFA grant 2011-67003-30371), the United States Department of Energy (AmeriFlux contract 7079856), and the National Science Foundation (grant EF-1241960). We thank Matteo Detto and another anonymous reviewer for helpful comments to improve the manuscript.
Publisher Copyright:
©2015. American Geophysical Union. All Rights Reserved.
PY - 2016/1/1
Y1 - 2016/1/1
N2 - Methane (CH4) exchange in wetlands is complex, involving nonlinear asynchronous processes across diverse time scales. These processes and time scales are poorly characterized at the whole-ecosystem level, yet are crucial for accurate representation of CH4 exchange in process models. We used a combination of wavelet analysis and information theory to analyze interactions between whole-ecosystem CH4 flux and biophysical drivers in two restored wetlands of Northern California from hourly to seasonal time scales, explicitly questioning assumptions of linear, synchronous, single-scale analysis. Although seasonal variability in CH4 exchange was dominantly and synchronously controlled by soil temperature, water table fluctuations, and plant activity were important synchronous and asynchronous controls at shorter time scales that propagated to the seasonal scale. Intermittent, subsurface water table decline promoted short-term pulses of methane emission but ultimately decreased seasonal CH4 emission through subsequent inhibition after rewetting. Methane efflux also shared information with evapotranspiration from hourly to multiday scales and the strength and timing of hourly and diel interactions suggested the strong importance of internal gas transport in regulating short-term emission. Traditional linear correlation analysis was generally capable of capturing the major diel and seasonal relationships, but mesoscale, asynchronous interactions and nonlinear, cross-scale effects were unresolved yet important for a deeper understanding of methane flux dynamics. We encourage wider use of these methods to aid interpretation and modeling of long-term continuous measurements of trace gas and energy exchange.
AB - Methane (CH4) exchange in wetlands is complex, involving nonlinear asynchronous processes across diverse time scales. These processes and time scales are poorly characterized at the whole-ecosystem level, yet are crucial for accurate representation of CH4 exchange in process models. We used a combination of wavelet analysis and information theory to analyze interactions between whole-ecosystem CH4 flux and biophysical drivers in two restored wetlands of Northern California from hourly to seasonal time scales, explicitly questioning assumptions of linear, synchronous, single-scale analysis. Although seasonal variability in CH4 exchange was dominantly and synchronously controlled by soil temperature, water table fluctuations, and plant activity were important synchronous and asynchronous controls at shorter time scales that propagated to the seasonal scale. Intermittent, subsurface water table decline promoted short-term pulses of methane emission but ultimately decreased seasonal CH4 emission through subsequent inhibition after rewetting. Methane efflux also shared information with evapotranspiration from hourly to multiday scales and the strength and timing of hourly and diel interactions suggested the strong importance of internal gas transport in regulating short-term emission. Traditional linear correlation analysis was generally capable of capturing the major diel and seasonal relationships, but mesoscale, asynchronous interactions and nonlinear, cross-scale effects were unresolved yet important for a deeper understanding of methane flux dynamics. We encourage wider use of these methods to aid interpretation and modeling of long-term continuous measurements of trace gas and energy exchange.
KW - biosphere-atmosphere interactions
KW - dynamical process networks
KW - eddy covariance
KW - methane
KW - multiresolution analysis
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U2 - 10.1002/2015JG003054
DO - 10.1002/2015JG003054
M3 - Article
AN - SCOPUS:84958125539
SN - 2169-8953
VL - 121
SP - 188
EP - 204
JO - Journal of Geophysical Research: Biogeosciences
JF - Journal of Geophysical Research: Biogeosciences
IS - 1
ER -