Annual methane emissions from degraded alpine wetlands in the eastern Tibetan Plateau.

Grazing-oriented drainage of alpine/boreal wetlands has been broadly implemented to meet the increasing demand for animal products. However, the annual methane (CH) emissions from alpine fens degraded due to drainage for grazing have not been well characterized due to a lack of year-round observations. In this study, the year-round CH fluxes from a degraded alpine fen that is typical in the Tibetan Plateau (TP) were measured. The temperature sensitivity of the CH emissions during the nongrowing season (NGS) was different between the microsites with and without CH uptake during the growing season (GS), showing apparent activation energy of 59-61 vs. 22-43 kJ mol (or variation folds induced by the 10-degree change (i.e., Q): 2.61-2.74 vs. 1.38-1.91). The CH emissions amounted to 0.2-63.3 kg C ha yr (with -0.8 to 41.4 kg C ha and 0.9 to 21.9 kg C ha in the GS and NGS, respectively), which were significantly (P < 0.05) related to the distances to the drainage ditch or water tables across the six microsites. As a key factor, the water table determined the role of the CH emissions during freezing/thawing. For cool/cold/alpine wetlands with no CH uptake in the GS, a mean factor of 1.52 (within a range of 1.00-2.44 at the 95% confidence interval), corresponding to an NGS contribution of 34% (ranging from 0 to 59%), was recommended to upscale the GS emissions to annual totals. Degradation of the native peat marshes in the Zoige region (originally the largest area of alpine wetlands) due to intentional drainage has greatly reduced the quantities of CH emissions. Additional studies are still needed to minimize the large uncertainties in CH emissions estimates for the changes in alpine wetlands in this region and for the entire TP.