磁法探测上海市掩埋煤气凝水井

本文论述了在城市中探测掩埋煤气凝水井的一种磁测方法,对由凝水井产生的磁场及磁场梯度进行了正演计算,对城市环境中的干扰背景磁场进行了理论分析,指出采用磁梯度探测方法能够有效的压制干扰背景磁场,突出有效异常,是城市中进行磁法探测的一种简便有效的方法。文中还就探测方法及磁梯度异常的反演计算进行了讨论。     

Glacial-Interglacial Atmospheric CO2 Change—The Glacial Burial Hypothesis

Organic carbon buried under the great ice sheets of the Northern Hemisphere is suggested to be the missing link in the atmospheric CO2 change over the glacial-interglacial cycles. At glaciation, the advancement of continental ice sheets buries vegetation and soil carbon accumulated during warmer pe-riods. At deglaciation, this burial carbon is released back into the atmosphere. In a simulation over two glacial-interglacial cycles using a synchronously coupled atmosphere-land-ocean carbon model forced by reconstructed climate change, it is found that there is a 547-Gt terrestrial carbon release from glacial maximum to interglacial, resulting in a 60-Gt (about 30-ppmv) increase in the atmospheric CO2, with the remainder absorbed by the ocean in a scenario in which ocean acts as a passive buffer. This is in contrast to previous estimates of a land uptake at deglaciation. This carbon source originates from glacial burial,continental shelf, and other land areas in response to changes in ice cover, sea level, and climate. The input of light isotope enriched terrestrial carbon causes atmospheric δ^13C to drop by about 0.3‰ at deglaciation,followed by a rapid rise towards a high interglacial value in response to oceanic warming and regrowth on land. Together with other ocean based mechanisms such as change in ocean temperature, the glacial burial hypothesis may offer a full explanation of the observed 80-100-ppmv atmospheric CO2 change.     

A comparative study of waste landfill disposal in different countries

This study draws attention to the fact that natural processes can mobilize thallium （Tl）, a highly toxic metal, which may enter the food chain with severe health impacts on the local human population. A rural area having independent Tl mineralization in southwestern Guizhou, China, was chosen for a pilot study. Tl contents of soils extracted by HNO3 in the study area range from 35-165 mg/kg in soils from the mining area, 14-78 mg/kg in alluvial deposits downstream, and 〈0.2-0.5 mg/kg in soils from the background area. Tl contents in ammonium acetate EDTA-extracted fraction are 0.013-1.3 mg/kg, less than 1% of concentration in HNO3-extracted fraction. The amounts of Tl in NH4Ac-extracted fraction were thought to be more exchangeable and bioavailable, i.e., immediately available to plants and/or available to plant roots over a period of years. Tl concentration in crops exhibits species-dependent preferences. The enrichment of Tl in edible crop species decreases in the following order： green cabbage〉chili〉Chinese cabbage〉rice〉com. The highest level of Tl in green cabbage is up to 500 mg/kg （DW）, surpassing the values of Tl in the soils （13-59 mg/kg）. The enrichment factor for TI in green cabbage is up to 1-10 when considering the HNO3-extracted Tl, but the factor highly rises to 30-1300 while considering the NH4Ac-extracted Tl. The average daily uptake of Tl by the local villagers through consumption of locally planted crops was estimated at about 1.9 mg per person, which is 50 times the daily ingestion from the Tl-free background area.