Stable isotope tracer method for gross fluxes

Building upon stable isotope dilution methods for CH4, our group developed a stable isotope tracer technique using 13C labeled methyl halides to quantify gross emission and consumption fluxes. This was applied in laboratory incubations and also in field flux studies. This allowed for the simultaneously search for new plant sources while quantifying the soil sink in situ. Soil uptake estimates for Kansas tallgrass prairie (Rhew, 2011), peatland pastures (Khan, Whelan and Rhew, 2012; Khan et al, 2013), and coastal salt marshes in northern California (Rhew and Mazeas, 2010) were combined with earlier work on boreal forest (Rhew, Aydin, and Saltzman, 2003), tundra (Teh et al., 2009), shortgrass steppe (Teh et al., 2008), annual grasslands (Rhew and Abel, 2007) and oak-savannah woodland (Rhew et al. 2010). These provided an estimate the soil sink that was about 10-70% lower than prior estimated ranges (yielding a longer partial lifetime), resolving a portion of the missing source problem and reducing the soil sink uncertainty (Montzka et al., 2011). This work also demonstrated that there was a corresponding soil sink for CH3Cl, slightly exacerbating the imbalance for that compound (e.g., Rhew et al., 2010).