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An ecosystem simulation model for methane production and emission from wetlands
Author(s) -
Potter Christopher S.
Publication year - 1997
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/97gb02302
Subject(s) - environmental science , wetland , methane , methanogenesis , ecosystem , soil water , hydrology (agriculture) , water table , carbon cycle , primary production , flux (metallurgy) , biosphere , soil science , ecology , groundwater , geology , chemistry , organic chemistry , geotechnical engineering , biology
Previous experimental studies suggest that methane emission from wetlands is influenced by multiple interactive pathways of gas production and transport through soil and sediment layers to the atmosphere. The objective of this study is to evaluate a new simulation model of methane production and emission in wetland soils that was developed initially to help identify key processes that regulate methanogenesis and net flux of CH 4 to the air but which is designed ultimately for regional simulation using remotely sensed inputs for land cover characteristics. The foundation for these computer simulations is based on a well‐documented model (Carnegie‐Ames‐Stanford Approach, CASA) of ecosystem production and carbon cycling in the terrestrial biosphere. Modifications to represent flooded wetland soils and anaerobic decomposition include three new submodels for (1) layered soil temperature and water table depth (WTD) as a function of daily climate drivers, (2) CH 4 production within the anoxic soil layer as a function of WTD and CO 2 production under poorly drained conditions, and (3) CH 4 gaseous transport pathways (molecular diffusion, ebullition, and plant vascular transport) as a function of WTD and ecosystem type. The model was applied and tested using climate and ecological data to characterize tundra wetland sites near Fairbanks, Alaska, studied previously by Whalen and Reeburgh [1992]. Comparison of model predictions to measurements of soil temperature and thaw depth, water table depth, and CH 4 emissions over a 2‐year period suggest that intersite differences in soil physical conditions and methane fluxes could be reproduced accurately for selected periods. Day‐to‐day comparison of predicted emissions to measured CH 4 flux rates reveals good agreement during the early part of the thaw season, but the model tends to underestimate production of CH 4 during the months of July and August in both test years. Important seasonal effects, including that of falling WTD during these periods, are apparently overlooked in the model formulation. Nevertheless, reasonably close agreement was achieved between the model's mean daily and seasonal estimates of CH 4 flux and observed emission rates for northern wetland ecosystems. Several features of the model are identified as crucial to more accurate prediction of wetland methane emission, including the capacity to incorporate influences of localized topographic and hydrologic features on site‐specific soil temperature and WTD dynamics and mechanistic simulation of methane emission transport pathways from within the soil profile.