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In this study, we identified ecological pressures on grassland ecosystems and adaptive countermeasures in Northern China. Our research revealed that the main sources of these pressures included population growth, economic development, resources exploitation, and global climate change, with human-related activities being overriding factors. Overgrazing was an important reason for grassland imbalance, causing soil erosion and desertification, especially during the sensitive spring greening phase. In steppe zones, commercial coal mining was destructive to the ecological environment. Regarding long-term strategies, we recommend that policy-makers devote more consideration to a new conceptual approach for transforming grasslands through shifting the focus from the grassland’s traditional production functions to their ecological functions. Applying this concept, adaptive countermeasures should be developed to reduce human impacts based on the environmental capacities of grasslands. Moreover, we recommend the de...

In order to analyze the response of tree radial growth on the climate change in the semi-arid area,the tree-ring width chronology of Pinus sylvestris var.mongolica in Hulunbuir,Inner Mongolia,including the standard chronology(STD),residual chronology(RES) and autoregressive chronology(ARS),was developed by fitting a negative exponential in this paper.According to the analysis on statistical characteristics,STD chronology showed quite well correlation between samples of different trees(correlation coefficient between trees,namely r = 0.520,P 0.01),indicating good consistency of variance characteristics of the ring-width among different trees,and thus the climate information recorded by those sampled trees can be regarded as reliable.The relationship between ring width and climate factors such as monthly mean precipitation and temperature from the previous October to current October was analyzed by correlation analysis and response function analysis during the observation period(1952—2008).The results indicate that the tree-ring width is negatively correlated to the monthly mean temperature,and the data shows a significant negative correlation from June to September in the current year(P 0.05).The mean temperature,especially the maximum temperature from June to August may constrain tree growth indirectly due to the enhanced evapotranspiration and decreased availability of soil moisture.The tree-ring width is significantly positively correlated to the monthly precipitation from May to August in the current year(P 0.05),and the highest correlation coefficient is observed between tree-ring width and the precipitation of current July(r=0.394,P0.05).Low total annual precipitation is generally regarded as the main factor to constrain the growth of trees,indicating a clear physiological sense for the notable positive correlation between tree-ring width index and precipitation.There is no significant correlation between the tree-ring width and the precipitation from previous December to current April,but in general they were positively correlated.The tree-ring width chronology is significantly positively correlated with the Palmer Drought Severity Index(PDSI) from last October to current October during 1951—2005,which comprehensively reflects the effect of available soil moisture,precipitation and temperature,especially during May.The response function analysis showed that the chronology is significantly correlated with the average temperature from June to July,the amount of precipitation from May to July of the current year,and that of last October,and positively related to the PDSI from May to July.These results show that the tree-ring width of Pinus sylvestris var.mongolica in Hulunbuir is affected by the temperature and precipitation in the growing seasons simultaneously,but the effect of precipitation on the tree radial growth is much greater than that of temperature on the yearly scale.In general,precipitation is a direct limiting factor to the radial growth of Pinus sylvestris var.mongolica in Hulunbuir area,while the temperature is an indirect limiting factor.Namely,the radial growth of Pinus sylvestris var.mongolica is more sensitive to precipitation.This study will be helpful for the precipitation and temperature reconstruction of Hulunbuir region.

Our world is facing water and energy shortage. As a relatively new process, membrane distillation (MD) is being investigated as a low cost and energy saving alternative to conventional separation processes such as distillation and reverse osmosis since 1990s. As a result of material limit, the development of membrane distillation has not yet come to the commercial scale. But, it has become a hopeful technology of the future. The objective of this research is to develop novel nanofiber membranes for seawater desalination by air gap membrane distillation (AGMD). The concept of novel nanofiber membranes is based on the electro-spinning technology. By using electro-spinning method, a highly hydrophobic material (PVDF, poly vinylidene fluoride) was spun to filaments with diameters in nanometer range. The PVDF nanofibers turn into a nanofiber non-woven mat or web and bring high hydrophobicity and a highly open pore structure. This further fulfils the requirements for the MD membranes with reduced mass transport resistance and temperature polarization. Thus, membranes with high MD fluxes are expected. In Part I of the current research, hydrophilic and hydrophobic polymers and a polymer blend (PVDF, PVDF/PVP, PS, PES, PEI, PVC, PC, PAN, Nomex (PA), PVA and Collagen) were used for electro-spinning to generate naonofibers and nanofiber membranes. The electro-spinning parameters that affect the structure and other properties of the membrane and the MD membrane performance were identified. They include spinning dope concentration, solution feed rate, spinning voltage and naonofiber collect distance. The electro-spinning parameters were then optimized for obtaining the best performance data. The PVDF nanofiber membranes were characterized by SEM, AFM, DSC, measurement of LEPw (liquid entry pressure of water), equilibrium contact angle and particle separation. It was found that the pore size of the PVDF nanofiber membrane was around 1.5 mum. The equilibrium contact angle of some nanofiber membranes were above 120°. It shows that the novel membranes have a very open pore structure and are highly hydrophobic. Those characteristics are exactly what are needed for MD membranes. In Part II of the current research work, a novel PVDF nanofiber membrane was tested for saline water desalination by AGMD (air gap membrane distillation). Desalination by AGMD was carried out for various sodium chloride concentrations in feed (1 to 22 wt%) at the feed solution and cooling water temperature difference of 60°C. Above 99% salt rejection and above 8 kg/m 2h flux was obtained. As well, ethanol/water separation was investigated by using 5 and 10 wt % aqueous ethanol solution. Two theoretical models were developed to simulate the AGMD process; the first model was developed to describe the AGMD process based on the mass and heat transfer through the membrane, while the second model deals with the transfer of volatile component through the air gap. The experimental flux value fits the second model very well. It shows that the air gap is the dominating stage for the heat transfer of the AGMD process. In an early stage of this work, polypropylene (PP) was chosen to prepare membranes of high hydrophobicity and high porosity for membrane distillation by a solution casting method. The results are reported in Appendix I. This method, even though novel, was not quite appropriate to fabricate membranes with hydrophobicity and porosity high enough for MD application. Howevere, the microporous PP membranes so prepared seem to have a great potential for other separation applications than MD.