Xi Haiyang

Comprehensive evaluation and indicator system of land desertification in the Heihe River Basin

Two landscape evaluation approaches, an integrated model and an ecological analysis method, based on landscape elements and environmental quality, respectively, were used to describe land desertification in the Heihe River Basin of northwestern China, by evaluating the current state of the local ecosystems and environment. Based on national water-quality criteria and fuzzy cluster analysis methods, surface water quality was divided into 5 grades with corresponding evaluation scores (evaluation rating threshold of water pollution), while groundwater quality was divided into 5 grades based on salinity and solute chemistry. For grassland ecosystems, grass yield (biomass) and types were the main indicators used. The soil component was described according to factors including its nutrient content, thickness, texture and degree of desertification, for a total of 11 evaluation indicators. Total vegetation cover is one of the 5 indicators chosen to describe the plant ecosystem. Based on conditions currently prevailing in the study region, evaluation factors such as total output value of agricultural, industrial, forestry and animal husbandry activities, the ratio of irrigation area to farmland area, the mean output return per unit area farmland, the level of education and per capital income were selected among others to characterize the social and economic situation. In total, 32 typical environment evaluation factors were selected, classifying land desertification in the region into four zones.

Effect of climatic changes and human activity on soil carbon in desertified regions of China

A total of 340 soil samples from 17 different types of sandy land regions in China were analyzed for soil organic carbon (SOC). Stepwise regression served to identify correlations betweenSOCand a number of climatic factors measured at the sampling sites: winter, summer, nighttime and daytime air temperatures (AT) and precipitation. In desertified lands SOC showed a direct correlation with precipitation, but no significant relationship with the mean air temperature. However, in northwest and northeast China decreases in SOC were linked to rises in day/night and seasonal temperatures, while in north China they were linked to a rise in mean temperature. Over the entire study period (1950–1990), precipitation in the region decreased by 25 mm decade-1, while the mean air temperature increased by 0.14◦, 0.28◦ and 0.15◦ decade-1 in the northwest, northeast and north central regions, respectively. Driven by rises in day/night and seasonal temperatures, long-term alterations to global ecosystem processes, particularly the carbon cycle, may significantly alter the number and diversity of plants in desertified ecosystems. Based on multiple regression analysis, over the past 40 years, about 20% of emissions from SOC in the northeast were attributable to air temperature; in the north central region 31 and 16% of emissions were attributable to precipitation and mean AT, respectively; while in the northwest 28, 18 and 32% of the emissions were attributable to mean AT, nighttime temperature, and decreasing precipitation, respectively. It is obvious that human activities are the main single causative factor in the release of SOC-derived greenhouse gases to the atmosphere from desertified areas.

Ejina Desert Oasis: A Fragile "Ecological Screen" in Inland Region of Northwest China

The deterioration of global eco-environment is seriously threatening human development, this is particularly true for most arid and semiarid zones in the world due to dry climate, meagre water resource, fragile ecosystem and prominent contradiction between the environment and development. How can we conduct eco-environmental construction is a difficult problem confronting people in these regions. This paper, taking northwest Chinas dry land miniature - Ejina desert oasis at the terminus of the Heihe River as an example and starting with the regions eco-environmental evolution, elucidates the cause of arid eco-environmental deterioration - interacted result of natural and human factors, analyze the restorability of eco-environment, discusses the problems in the eco-environmental construction in arid regions, and revealed results have a common reference value to the study of environmental evolution and eco-environmental construction in arid regions under the combined actions of natural and human factors.