Many studies on global climate have forecast major changes in the amounts and spatial patterns of precipitation that may significantly affect temperate grasslands in arid and semi-arid regions. As a part of ChinaFLUX, eddy covariance flux measurements were made at a semi-arid Leymus chinensis steppe in Inner Mongolia, China during 2003–2004 to quantify the response of carbon exchange to environmental changes. Results showed that gross ecosystem production (FGEP) and ecosystem respiration (Reco) of the steppe were significantly depressed by water stress due to lack of precipitation during the growing season. Temperature was the dominant factor affecting FGEP and Reco in 2003, whereas soil moisture imposed a significant influence on both Reco and FGEP in 2004. Under wet conditions, Reco showed an exponentially increasing trend with temperature (Q10 = 2.0), but an apparent reduction in the value of Reco and its temperature sensitivity were observed during the periods of water stress (Q10=1.6). Both heat and water stress can cause decrease in FGEP. The seasonality of ecosystem carbon exchange was strongly correlated with the variation of precipitation. With less precipitation in 2003, the steppe sequestrated carbon in June and July, and went into a senescence in early August due to water stress. As compared to 2003, the severe drought during the spring of 2004 delayed the growth of the steppe until late June, and the steppe became a CO2 sink from early July until mid-September, with ample precipitation in August. The semi-arid steppe released a total of 9.7 g C·m−2 from May 16 to the end of September 2003, whereas the net carbon budget during the same period in 2004 was close to zero. Long-term measurements over various grasslands are needed to quantify carbon balance in temperate grasslands.
A sampling campaign of aerosols over Urumqi from 2001–2007 and soil samples in the surrounding areas were carried out to investigate
the severe air pollution in Urumqi, a typical inland city, located in the center of Asia. Urumqi is one of the heavy polluted
cities in the world, as the days of haze spanned over one third of the year and accounted for 60–80% of the heating period
for the past 6 years. High concentration of fine aerosols, frequent occurrence, and rapid formation of heavy haze were the
three main characteristics. With comparison of the pollution elements, As, Cd, and S, and the ratio of Ca/Al in aerosols and
soils in those sites located on the south of Jungger Basin as tracers, it was found that As, Cd, and S highly enriched in
the aerosols over urban Urumqi were not only from the re-suspended road dust but also from the soil transported from south
of the Jungger Basin. Different from the most cities in China, the high concentration of sulfate in Urumqi was partially from
the primary soil dust transported from the surrounding areas. The mixing of the local anthropogenic aerosols with the soil
transported from outside the city was the main source of the high sulfate concentration. Ammonium salts were higher than the
summed equivalents of SO42−, NO3−, and Cl− in Urumqi and much higher than that in other Chinese cities. The total water soluble ions and the total ammonium salts were
as high as 57.8% and 51.0% in PM2.5. The high concentration of soluble salts with high hygroscopicity, especially ammonium and sulfate salts, were the main factors
contributing to the heavy haze over Urumqi. 相似文献
A new three-dimensional semi-implicit finite-volume ocean model has been developed for simulating the coastal ocean circulation, which is based on the staggered C -unstructured non-orthogonal grid in the horizontal direction and z -level grid in the vertical direction. The three-dimensional model is discretized by the semi-implicit finite-volume method, in that the free-surface and the vertical diffusion are semi-implicit, thereby removing stability limitations associated with the surface gravity wave and vertical diffusion terms. The remaining terms in the momentum equations are discretized explicitly by an integral method. The partial cell method is used for resolving topography, which enables the model to better represent irregular topography. The model has been tested against analytical cases for wind and tidal oscillation circulation, and is applied to simulating the tidal flow in the Bohai Sea. The results are in good agreement both with the analytical solutions and measurement results. 相似文献