Spectral evidence for substrate availability rather than environmental control of methane emissions from a coastal forested wetland

  • Authors: Mitra, Bhaskar; Minick, Kevan; Miao, Guofang; Domec, Jean-Christophe; Prajapati, Prajaya; McNulty, Steve G.; Sun, Ge; King, John S.; Noormets, Asko
  • Publication Year: 2020
  • Publication Series: Scientific Journal (JRNL)
  • Source: Agricultural and Forest Meteorology
  • DOI: 10.1016/j.agrformet.2020.108062

Abstract

Knowledge of the dynamics of methane (CH4) fluxes across coastal freshwater forested wetlands, such as those found in the southeastern US remains limited. In the current study, we look at the spectral properties of ecosystem net CH4 exchange (NEECH4) time series, and its cospectral behavior with key environmental conditions (temperature (Ts5), water table (WTD) and atmospheric pressure (Pa)) and physiological fluxes (photosynthesis (GPP), transpiration (LE), sap flux (Js)) using data from a natural bottomland hardwood swamp in eastern North Carolina. NEECH4 fluxes were measured over five years (2012 – 2016) that included both wet and dry years. During the growing season, strong cospectral peaks at diurnal scale were detected between CH4 efflux and GPP, LE and Js. This suggests that the well understood diurnal cycles in the latter processes may affect CH4 production through substrate availability (GPP) and transport (sap flow and LE). The causality between different time series was established by the magnitude and consistency of phase shifts. The causal effect of Ts5 and Pa were ruled out because despite cospectral peaks with CH4, their phase relationships were inconsistent. The effect of fluctuations in WTD on CH4 efflux at synoptic scale lacked clear indications of causality, possibly due to time lags and hysteresis. The stronger cospectral peak with ecosystem scale LE rather than Js suggested that the evaporative component of LE contributed equally with plant transpiration. Hence, we conclude that while the emission of dissolved gases through plants likely takes place, it may not contribute to higher CH4 emissions as has been proposed by aerenchymatous gas transport in sedge wetlands. These findings can inform future model development by (i) highlighting the coupling between vegetation processes and CH4 emissions, and (ii) identifying specific and non-overlapping timescales for different driving factors.

  • Citation: Mitra, Bhaskar; Minick, Kevan; Miao, Guofang; Domec, Jean-Christophe; Prajapati, Prajaya; McNulty, Steve G.; Sun, Ge; King, John S.; Noormets, Asko. 2020. Spectral evidence for substrate availability rather than environmental control of methane emissions from a coastal forested wetland. Agricultural and Forest Meteorology. 291: 108062-. https://doi.org/10.1016/j.agrformet.2020.108062.
  • Keywords: Cross-scale analysis, Methane, Plant transportation, Wavelet analysis, Water table depth
  • Posted Date: September 21, 2020
  • Modified Date: September 21, 2020
  • Print Publications Are No Longer Available

    In an ongoing effort to be fiscally responsible, the Southern Research Station (SRS) will no longer produce and distribute hard copies of our publications. Many SRS publications are available at cost via the Government Printing Office (GPO). Electronic versions of publications may be downloaded, printed, and distributed.

    Publication Notes

    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
    • Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
    • To view this article, download the latest version of Adobe Acrobat Reader.