^(137)Cs在滇西与黔中地区散落的差异——青藏隆起对滇西地区全球性扩散大气污染物散落屏蔽效应的推断

THE DIFFERENTIALS OF FALLOUT^(137)Cs BETWEEN WESTERN YUNNAN AND CENTRAL GUIZHOU: IMPLICATION FOR THE BARRIER EFFECT OF QINGHAI-XIZANG UPLIFT ON GLOBAL ATMOSPHERIC POLLUTANTS IN YUNNAN-GUIZHOU PLATEAU

云贵高原是青藏隆起在南亚大陆形成的一个海拔梯度大、地势格局复杂的特异环境单元。该地域兼受东南季风与西南季风的交汇影响 ,是全球变化的敏感区之一。青藏隆起对云贵高原现代环境影响主要表现在 :1 )全球性大气扩散污染物的屏蔽效应和局地性大气扩散污染物的滞留效应 ;2 )区域化学风化的增强效应和物理侵蚀的梯级效应 ;3)地表环境地球化学过程的低纬度 -高海拔效应。核素示踪模式分析表明 :滇西与黔中地区之间137Cs自大气散落差异明显 [1 986年以前 ,洱海和红枫湖沉积物中137Cs散落的累计值分别为 ( 0 .1 1±0 .0 1 )Bq cm2 及 ( 0 .37± 0 .0 1 )Bq cm2 ],而7Be的散落相近。

Yunnan Guizhou Plateau,the middle tier on the eastern slope of Qinghai Xizang Plateau,is a complex geomorphic unit with a large altitude gradient in the South Asia. Impacts of the Qinghai Xizang uplift on the modern environment in the area mainly embody:(1) barrier effect of global atmospheric pollutants and detaining effect of local atmospheric pollutants;(2) enhancement of regional chemical weathering and altitude related effect of physical weathering;(3) low latitude and high altitude effect of environmental geochemical process of surface earth. Lake sediments embrace materials originating not only from watershed but also from atmospheric deposition. 137 Cs is an excellent tracer for watershed erosion and lake deposition. 7 Be is an ideal tracer for seasonally transportation of environmental particles. Differentials of 7 Be/ 137 Cs in the top soils between western Yunnan and central Guizhou show different characteristics of 137 Cs and 7 Be deposition accumulation in the two regions. 7 Be inventories in the sediments of Erhai Lake correspond to that in the soils of its watershed in the western Yunnan. 7 Be inventories in sediments of Hongfeng Lake are much higher than the average value in the soil profiles of its watershed. 137 Cs inventories in sediments of Hongfeng Lake is 7.1 times of the Erhai Lake. The model analysis indicated that 7 Be atmospheric deposition in western Yunnan was similar to central Guizhou. Prior to 1986, 137 Cs inventories from atmospheric fallout in the western Yunnan and the central Guizhou were (0.11±0.01) Bq/cm 2 and (0.37± 0.01 ) Bq/cm 2,respectively. This indicates that fallout 137 Cs in the western Yunnan was much lower than that in the central Guizhou. The regional differentials of the 137 Cs fallout reflect that the uplift of Qinghai Xizang Plateau would have a barrier effect on the precipitation of global atmospheric pollutants in the western Yunnan. \;