藏北牧区畜粪燃烧与养分流失的生态效应研究

藏北牧区是典型的高寒缺能、生态脆弱地区,长期以来以畜粪为主的能源结构在满足能源消费的同时,畜粪燃烧使得其中的有机质、养分排空,致使室内空气污染和草地物质循环受阻。本研究基于田野调查、实验分析、结合统计数据,分析了1988-2010年藏北牧区那曲、班戈和尼玛3县的牦牛排粪、牛粪燃用的时空过程,评估了牛粪燃用引起的有机质、养分直接排空流失效应。研究表明区域尺度的牛粪排放量主要取决于牦牛存栏数,那曲县、班戈县和尼玛县年均牦牛排粪量分别为15.1、6.5和4.8万t干物质(d M)。牛粪燃用量主要与乡村人口有关,那曲、班戈和尼玛年均牦牛粪燃用量分别为9.0、4.7和3.6万t d M。藏北牧区的牛粪燃用强度(牛粪燃用量与牛粪排放量之比)为70%,其中那曲县61%、班戈县72.2%、尼玛县76.8%。牛粪燃用后95%以上的有机碳、氮都直接释放到大气中了。那曲、班戈和尼玛年均释放的氮为0.19、0.10、0.08万t。与牛粪还田相比,牦牛粪大量燃烧引起土壤有机质和速效磷含量降低,草地初级生产力降低。未来,应该大力发展替代能源、降低牛粪燃用强度,加大牛粪、粪灰还田力度以优化牛粪利用方式,协调牛粪的燃料和肥料功能。

Yak dung use as fuel and nutrient loss in the Northern Tibetan Plateau

The pastoral area on the northern Tibetan Plateau is characterized by high-frigidity, ecological frangibility and energy shortages. Yak dung is used as a fuel and plays an important role in the region's energy mix;however,the impact,including nutrient loss and nutrient cycling, interrupted by dung combustion has become a serious problem. Using field surveys,in-lab analysis and statistical data,we analyzed the spatial-temporal dynamics of yak dung produced and combusted as fuel in Nagqu,Bangoin and Nyima on the Tibetan Plateau since 1988. Organic carbon and nitrogen nutrient loss from dung combustion was assessed. We found that yak dung production depends on the number of yak at a regional scale. The annual mean yak dung produced in Nagqu,Bangoin and Nyima was 151,65 and 48 thousand tonne dry material(dM)from 1988-2010. Yak dung combustion depends mainly on the resident population,and the annual mean yak dung combusted as fuel in Nagqu,Bangoin and Nyima was 90,47 and 36 thousand tonne dM during the period. The intensity of yak dung combustion (ratio of dung combustion to dung produced)in this part of the Tibetan Plateau is 70%:Nagqu 61%,Bangoin 72.2% and Nyima 76.8%. Over 95% organic carbon and nitrogen contained in yak dung is volatilized after dung combustion. The loss of nitrogen from dung combustion in Nagqu,Bangoin and Nyima is 1.9,1.0 and 0.8 thousand tonne annually. Compared to returning dung back to soil,dung combustion results in a decrease in the content of available phosphorus and NPP. In the future,measures such as substituting dung combustion for new energy and hydropower and returning dung and ash from dung combustion to the soil may optimize dung utilization and the function of dung as a fuel and fertilizer.