Quantifying terrestrial and aquatic ecosystem methane emissions with process-based biogeochemistry and atmospheric transport and chemistry models

• Main Author: Tan, Zeli
• Other Authors: Zhuang, Qianlai
• Format: Text
• Language: English
• Published: Purdue University 2015
• Subjects: Biogeochemistry|Atmospheric sciences; Arctic; Thermokarst; Alaska; Siberia
• Online Access: https://docs.lib.purdue.edu/dissertations/AAI10075596

To improve the quantification of methane emissions from Arctic wetlands and lakes, an integrated modeling framework was developed. It includes a newly developed process-based lake biogeochemical model and a widely used 4-D VAR inversion algorithm implemented with the nested grid high-resolution GEOS-Chem Adjoint model. The new process-based lake biogeochemical model includes the processes of methane production, oxidation and transport within a one-dimensional sediment and water column. The model is validated using observational data from five lakes located in Siberia and Alaska, representing a large variety of environmental conditions in the Arctic. The modeled lake temperature, dissolved methane concentration and methane fluxes agree well with the observations. It is found that bubbling-rate-controlling nitrogen stripping is the most important factor in determining methane fraction in bubbles. Lake depth and ice cover thickness in shallow waters are also controlling factors. It demonstrates that the thawing of Pleistocene-aged organic-rich ice complex (yedoma) fuels sediment methanogenesis by supplying a large amount of labile organic carbon, resulting in high methane effluxes at thermokarst margins of yedoma lakes. By using the developed process-based lake biogeochemical model with geographical datasets, it is estimated that the annual mean methane emissions from Arctic lakes are on average 11.86 Tg yr-1 during 2004-2009, which is in the range of the recent estimates of 7.1-17.3 Tg yr-1 and is on the same order of the methane emissions from northern high-latitude wetlands. The methane emission rate varies spatially over high latitudes from 110.8 mg CH4 m-2 day-1 in Alaska to 12.7 mg CH4 m-2 day-1 in northern Europe. Under Representative Concentration Pathways (RCP) 2.6 and 8.5 future climate scenarios, when assuming the distribution of lakes unchanged, the methane emissions from Arctic lakes will increase by 10.3 and 16.2 Tg CH4 yr-1, respectively, by the end of the 21st century. By adapting a region-specific ...