Ecological Process Of Soil Salinization In Desert-oasis Complex

Soil salinization is one of the most important factors which affecting the stable ecological environment, desert-oasis complex, and a major obstacle for the sustainable development of agriculture. Considering the problem of soil salinization in the desert-oasis complex a case study was performed in two different watershed areas （Manas river basin and Yarkand river basin） in Xinjiang, to promote the social harmony and its effect on the economy."3S" technology, field sampling and analysis, and geostatistical interpolation method, were used to perform the systematic study for comparing the level of progress in these two river basins.It is observed that the ratio of development in Manas river basin is higher than Yarkand river basin during the period of1976to2013. To explore the reasons for this difference and to reduce ecological risk that can affect saline soil, we compared the spatial distribution patterns over time and studied the changes in the distribution area as well as differences in the saline soil type in desert-oasis complex. Interactions of natural and social factors were also studied on the salinization and following results have obtained:1) The distribution patterns of soil salinization in Yarkand river is mainly located in the oasis periphery, moreover4543.47km2saline land has reduced during1976to2013, showed overall downward trend in this period. Saline soil has transformed to the other landscape in which bare land is the most common land type, indicating the concern for ecological protection and need to improve bare land in to the other vegetative land types.2) The spatial distribution of saline soil in Yarkand river from upstream to downstream is different and the extent of soil salinization gradually increases from up to downstream, such as the mean values of the soil salinity in upstream, midstream and downstream were3.4g/kg,17.53g/kg and24.64g/kg, respectively. Different saline soil types were observed in these streams such as sulphate saline soil in upstream, chloride sulphate saline soil and sulfate chloride saline soil in midstream, while chloride saline was in the downstream. Extent of the salinization in the basin along the direction of the river was different, so salinization watershed area is located more close to the edge of the river e.g. Alluvial Fan, as compared to the downstream areas.3) Patterns of soil salinization in Manas river basin and their distribution process at large scale are related to the development of the small oasis, located in the desert-oasis has decreased year by year, during1976（2239.24km2） to2013（372.39km2）, so total saline soil area decreased about1866.14km2, in which nearly half of this area （931.33km2saline soil） has been converted into farm land.4) The degree of spatial scale soil salinization in Manas river from upstream to downstream is increasing and the average salt accumulation were3.4g/kg,13.23g/kg and17.37g/kg, respectively. Different saline soil types exists such as in upstream sulphate saline soil while in the downstream chloride saline soil, so variation in the streams was observed by saline ions. Spatial distribution of saline soil content in the basin increased from upstream to downstream in a continuous process, but high levels of saline soil in the zone is different from ancient river direction, indicating that the disturbance of human activity has changed the distribution saline soil pattern in the Manas river.5) The salinity of saline soil is increased from upstream to downstream in two river basins, and the types of saline soil are sulfate and the chloride similar in both basins, while the salinization level in Yarkand river basin is higher than the Manas river basin. The distribution ratio of saline soil ions (Cl-/SO₄^2-) is different in two basins, e.g. the Cl-/SO₄^2-values in Yarkand river basin are higher than the Manas river basin. The Cl-/SO₄^2- values from the upstream to the downstream were0.58,3.01,4.55in Yarkand river basin, while in Manas river basin were0.36,2.11, and3.76, respectively.6) The theory of Coupled Human and Natural Systems （CHANS） was used to analyze the reasons for the difference among ecological processes in desert-oasis complex, and it is observed that salinization of soil water and salt distribution in two basin, is due to the combined action of natural （climate, soil texture, topography, and shallow groundwater etc.） and social factors （population growth, application of the agricultural water conservation technologies etc.）.In this case study we used new methods of science and technology to get geographical information and observed that in desert-oasis complex, saline soil distribution patterns in ecological processes were quite different with the passage of time. The future perspectives of this research are very important especially for the regulation of saline soil areas into normal land and to provide a theoretical basis for the establishment of ecological desert-oasis complexes for sustainable development of agriculture.