Abstract
Greenhouse gas (GHG) emissions from livestock grazing systems are contributing to global warming. To examine the influence of yak grazing systems on GHG fluxes and relationships between GHG fluxes and environmental factors, we measured carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes over three key seasons in 2012 and 2013 from a range of potential sources, including: alpine meadows, dung patches, manure heaps and yak night pens, on the Qinghai-Tibetan Plateau. We also estimated the total annual global warming potential (GWP, CO2-equivalents) from family farm grazing yaks using our measured results and other published data. In this study, GHG fluxes per unit area from night pens and composting manure heaps were higher than from dung patches and alpine meadows. Increased moisture content and surface temperature of soil and manure were major factors increasing CO2 and CH4 fluxes. High contributions of CH4 and N2O (21.1% and 44.8%, respectively) to the annual total GWP budget (334.2 tonnes) strongly suggest these GHG other than CO2 should not be ignored when estimating GWP from the family farm grazing yaks on the Qinghai-Tibetan Plateau for the purposes of determining national and regional land use policies or compiling global GHG inventories.
Highlights
As the largest and highest grassland unit on the Eurasion continent, the Qinghai-Tibetan Plateau (QTP) covers an area of approx. 2.5 million km[2] and it is often referred to as the ‘Third Pole’, playing a critical climatic role, governing the Asian monsoon and it is the source of river systems that provide water to some 20% of the world’s population[10,11,12,13]
Some studies have reported that alpine meadows on the QTP acts as a weak CH4 sink during the growing season[18], excreta patches deposited onto grassland as “hotspot” of CH4 and N2O emissions[14], as well as feedlots as the significant N2O sources[16]; so far, they have not taken into account of the effects of excreta patches, expecially manure heaps and night pens, on greenhouse gas (GHG) emissions in the whole farm practices
CO2 emissions were significantly higher from dung patches than other sources in August 2012 (MSD = 200.5, P < 0.0001) and from both dung patches and manure heaps in August 2013 (MSD = 505.9, P = 0.0044), with no significant difference detected among sources in November 2013 (MSD = 194.3, P > 0.05)
Summary
As the largest and highest grassland unit on the Eurasion continent, the Qinghai-Tibetan Plateau (QTP) covers an area of approx. 2.5 million km[2] and it is often referred to as the ‘Third Pole’ (mostly situated at 4000 m above sea level), playing a critical climatic role, governing the Asian monsoon and it is the source of river systems that provide water to some 20% of the world’s population[10,11,12,13]. Some studies have reported that alpine meadows on the QTP acts as a weak CH4 sink during the growing season[18], excreta patches deposited onto grassland as “hotspot” of CH4 and N2O emissions[14], as well as feedlots as the significant N2O sources[16]; so far, they have not taken into account of the effects of excreta patches, expecially manure heaps and night pens, on GHG emissions in the whole farm practices. The overall objective of our study was to quantify GHG emissions from yak farming, taking account in the measurement protocol of farm practices such as use of night pens and manure heaps, as well as evironmental factors. The specific aims of this study were to (1) observe temporal variation in CH4, CO2 and N2O fluxes of key sources (alpine meadows, dung patches, manure heaps and night pens) under yak grazing systems across different seasons(early growing, peak growing and non-growing season); (2) evaluate relationships between GHG fluxes and physico-chemical factors (i.e. surface temperature (ST), moisture content (MC), total organic carbon (TOC), total nitrogrn (TN), microbial bimass carbon (MBC) and microbial biomass nitrogrn (MBN)); (3) estimate the total annual GWP (CO2-equivalents) and the contribution of each gas from a typical family farm grazing yaks
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