Fluxes of CO 2, CH 4, and N 2O in an alpine meadow affected by yak excreta on the Qinghai-Tibetan plateau during summer grazing periods

Abstract

To assess the impacts of yak excreta patches on greenhouse gas (GHG) fluxes in the alpine meadow of the Qinghai-Tibetan plateau, methane (CH 4), carbon dioxide (CO 2), and nitrous oxide (N 2O) fluxes were measured for the first time from experimental excreta patches placed on the meadow during the summer grazing seasons in 2005 and 2006. Dung patches were CH 4 sources (average 586 μg m −2 h −1 in 2005 and 199 μg m −2 h −1 in 2006) during the investigation period of two years, while urine patches (average −31 μg m −2 h −1 in 2005 and −33 μg m −2 h −1 in 2006) and control plots (average −28 μg m −2 h −1 in 2005 and −30 μg m −2 h −1 in 2006) consumed CH 4. The cumulative CO 2 emission for dung patches was about 36–50% higher than control plots during the experimental period in 2005 and 2006. The cumulative N 2O emissions for both urine and dung patches were 2.1–3.7 and 1.8–3.5 times greater than control plots in 2005 and 2006, respectively. Soil water-filled pore space (WFPS) explained 35% and 36% of CH 4 flux variation for urine patches and control plots, respectively. Soil temperature explained 40–75% of temporal variation of CO 2 emissions for all treatments. Temporal N 2O flux variation in urine patches (34%), dung patches (48%), and control (56%) plots was mainly driven by the simultaneous effect of soil temperature and WFPS. Although yak excreta patches significantly affected GHG fluxes, their contributions to the whole grazing alpine meadow in terms of CO 2 equivalents are limited under the moderate grazing intensity (1.45 yak ha −1). However, the contributions of excreta patches to N 2O emissions are not negligible when estimating N 2O emissions in the grazing meadow. In this study, the N 2O emission factor of yak excreta patches varied with year (about 0.9–1.0%, and 0.1–0.2% in 2005 and 2006, respectively), which was lower than IPCC default value of 2%.