ch4 placement in driver will cause problems if BeTR is used for nitrogen

**Bill Sacks < sacks@ucar.edu > - 2016-02-22 10:27:57 -0700**
**Bugzilla Id:** [2288](http://bugz.cgd.ucar.edu/show_bug.cgi?id=2288)
**Bugzilla CC:** andre@ucar.edu, dlawren@ucar.edu, gbisht@lbl.gov, jinyuntang@lbl.gov, oleson@ucar.edu, rfisher@ucar.edu,

The fix for bug 2225 and bug 2287, brought to the trunk in clm4_5_8_r168 (which returns the call to ch4 to where it was in clm4_5_12 and earlier), will cause problems if BeTR is ever used for nitrogen.

Here is an email from Jinyun about this:

> Too bad that move caused the travel. My original intention was to make a
> consistent tracking of nitrogen leaching in betr with hydrology code with the
> active ch4 cycle. As it is now in tag 168, a serious inconsistency would arise
> if one use betr to track nitrogen cycle with active ch4 code. However, since
> there is no intent to do active bgc in betr, the flip back is OK. Yet, I do
> suspect this flip back will cause trouble down the road if people intend to
> use betr for carbon isotope transport, even though I personally will not do
> it. Therefore, my suggestion is either to separate the set value stuff for
> ch4, so it will not zero out methane flux or indicate in somewhere that
> caution against people to use betr for purpose other than water isotopes (this
> basically push the problem to the future, and someone has to implement the
> separation strategy again).

Without having a very good understanding of this, I agree that separating the set value stuff for ch4 seems like the best solution here. Once that is done, the change to the driver sequencing in clm4_5_8_r168 should be reverted.