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A new dinuclear europium cluster (Eu-cluster) is synthesized and the exact structure is determined by single-crystal X-ray diffraction. The formula of the Eu-cluster is determined to be [Eu 2 (4-Msal) 6 (phen) 2 (H 2 O) 2 ] (4-Msal = 4-methylsalicylic acid, phen = phenanthroline), it crystallizes in the triclinic space group P -1, with a = 9.1193(8) Å, b = 13.0855(10) Å, c = 14.0981(9) Å, α = 103.159(6)°, β = 94.192(6)°, γ = 100.632(7)°, V = 1598.3(2) Å 3 and Z = 1. Further investigation reveals that the Eu-cluster is a highly sensitive and selective methylmercury (CH 3 Hg + ) sensor. To the best of our knowledge, this is the first CH 3 Hg + sensor based on lanthanide clusters/complexes. The responsive behavior shows the sensing has excellent linearity in 1.4–3.8 μg L −1 μM. The LOD for sensing CH 3 Hg + is 0.8 μg L −1 , which meets the standard of Chinese environmental quality standard for agricultural and industrial water. Interestingly, study also reveals the sensor is applicable in real water sensing. [ABSTRACT FROM AUTHOR]

Carbon fluxes were measured using a static chamber technique in an alpine steppe in the Qinghai-Tibet Plateau from July 2000 to July 2001. It was shown that carbon emissions decreased in autumn and increased in spring of the next year, with higher values in growth seasons than in winters. An exponential correlation ( Ecarbon= 0.22(exp(0.09 T) + ln(0.31 P+ 1)), R2= 0.77, P < 0.001) was shown between carbon emissions and environmental factors such as temperature ( T) and precipitation ( P). Using the daily temperature ( T) and total precipitation ( R), annual carbon emission from soil to the atmosphere was estimated to be 79.6 g C/m2, 46% of which was emitted by microbial respiration. Considering an average net primary production of 92.5 g C/m2 per year within the 2 year experiment, alpine steppes can take up 55.9 g CO2-C/m2 per year. This indicates that alpine steppes are a distinct carbon sink, although this carbon reservoir was quite small. [ABSTRACT FROM AUTHOR]

Soil carbon sequestration was estimated in a conifer forest and an alpine meadow on the Tibetan Plateau using a carbon-14 radioactive label provided by thermonuclear weapon tests (known as bomb-14C). Soil organic matter was physically separated into light and heavy fractions. The concentration spike of bomb-14C occurred at a soil depth of 4 cm in both the forest soil and the alpine meadow soil. Based on the depth of the bomb-14C spike, the carbon sequestration rate was determined to be 38.5 g C/m2 per year for the forest soil and 27.1 g C/m2 per year for the alpine meadow soil. Considering that more than 60% of soil organic carbon (SOC) is stored in the heavy fraction and the large area of alpine forests and meadows on the Tibetan Plateau, these alpine ecosystems might partially contribute to “the missing carbon sink”. [ABSTRACT FROM AUTHOR]

Horizontal and vertical variations of daily average CO_2 concentration above the wetland surface were studied in Xianghai National Nature Reserve of China in August, 2000. The primary purpose was to study spatial distribution characteristics of CO_2 concentration on the four levels of height (0.1 m, 0.6 m, 1.2 m and 2 m) and compare the differences of CO_2 concentration under different land covers. Results showed that daily average CO_2 concentration above wetland surface in Xianghai National Natural Reserve was lower than that above other wetlands in northeast China as well as the worldwide average, suggesting that Xianghai wetland absorbed CO_2 in August and acted as "sink" of CO_2. The horizontal variations on the four levels of height along the latitude were distinct, and had the changing tendency of "decreasing after increasing" with the increase of height. The areas with obvious variations were consistent on different levels of height, and those with the highest variations appeared above surface of shore, sloping field, Typha wetland and Phragmites wetland; the vertical variations were greatly different, with the higher variations in Phragmites wetland and Typha wetland, and the lands near the shore and the sloping field with the lower variations. Spatial variations of daily average CO_2 concentrations above wetland surface were affected by surface qualities and land covers. [ABSTRACT FROM AUTHOR]