Summary of the Article on CH4 Production in CLM:

CH4 Production in CLM
---------------------

1. Heterotrophic Respiration as a Proxy:
   - Since CLM does not represent wetland plant types or soil biogeochemistry, it uses gridcell-averaged decomposition rates as proxies.
   - The upland heterotrophic respiration is used to estimate the wetland decomposition rate, with the O2 consumption associated with anaerobic decomposition set to the unlimited version.

2. CH4 Production Calculation:
   - CH4 production at each soil level in the anaerobic portion is related to the gridcell estimate of heterotrophic respiration, corrected for soil temperature, pH, redox potential, and seasonal inundation fraction.
   - The temperature factor is set to 0 for temperatures at or below freezing in the single BGC soil level, but CH4 production continues below freezing in the vertically resolved BGC version.
   - The heterotrophic respiration is distributed among soil levels, with 50% associated with roots and the rest evenly divided among the top 0.28 m of soil for the single-layer BGC version.

3. Influencing Factors:
   - The pH factor (f_pH) is nominally set to 1, but a static spatial map of pH can be used.
   - The redox potential factor (f_pE) assumes a 30-day e-folding time for reduction of alternative electron acceptors.
   - As a non-default option, the Arah and Stephen (1998) estimate of the anaerobic fraction above the water table is applied.

4. O2 Demand Calculation:
   - The O2 required for heterotrophic decomposition, root respiration, and nitrification is estimated and used in the O2 mass balance solution.

5. Parameter Descriptions and Sensitivity Analysis:
   - A table is provided with details on the parameters used in the methane model, their baseline values, and sensitivity analysis ranges.