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Methane emission through ebullition from an estuarine mudflat: 2. Field observations and modeling of occurrence probability
Author(s) -
Chen Xi,
Schäfer Karina V. R.,
Slater Lee
Publication year - 2017
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2016wr019720
Subject(s) - environmental science , water level , estuary , methane , hydrology (agriculture) , wetland , atmospheric sciences , temperate climate , oceanography , geology , ecology , cartography , geotechnical engineering , geography , biology
Ebullition can transport methane (CH 4 ) at a much faster rate than other pathways, albeit over limited time and area, in wetland soils and sediments. However, field observations present large uncertainties in ebullition occurrences and statistic models are needed to describe the function relationship between probability of ebullition occurrence and water level changes. A flow‐through chamber was designed and installed in a mudflat of an estuarine temperate marsh. Episodic increases in CH 4 concentration signaling ebullition events were observed during ebbing tides (15 events over 456 ebbing tides) and occasionally during flooding tides (4 events over 455 flooding tides). Ebullition occurrence functions were defined using logistic regression as the relative initial and end water levels, as well as tidal amplitudes were found to be the key functional variables related to ebullition events. Ebullition of methane was restricted by a surface frozen layer during winter; melting of this layer during spring thaw caused increases in CH 4 concentration, with ebullition fluxes similar to those associated with large fluctuations in water level around spring tides. Our findings suggest that initial and end relative water levels, in addition to tidal amplitude, partly regulate ebullition events in tidal wetlands, modulated by the lunar cycle, storage of gas bubbles at different depths and seasonal changes in the surface frozen layer. Maximum tidal strength over a few days, rather than hourly water level, may be more closely associated with the possibility of ebullition occurrence as it represents a trade‐off time scale in between hourly and lunar periods.