Study On The Spatial Variability Of Saline Soil And Groundwater Characteristics In Ogan-Kuqa Oasis

The diversity of climate, parent rock, topography, animals and plants in variousregions on earth, leading to distinct difference on soil physio-chemical and biologicalproperties in the formation process of a variety of soil types. Land degradation (e.g.,salinization) and its evolution in a given region will inevitably cause the variability ofsoil characteristics in specific temporal and spatial scales. Therefore, it is necessary tostudy spatio-temporal variability of soil properties in time and space sequence to moreaccurately understand the relationship between the spatio-temporal variability of soilcharacteristics and its regional ecological environment.In this paper, we used RS/GIS technology with the combination of correlationanalysis, traditional statistics and geostatistics methods. Firstly, we conducted aresearch on spatio-temporal distributions of saline soil-based landscape types and itsvariation tendency. Then, we analyzed the temporal and spatial variation of soilproperties, such as soil salinity, conductivity, moisture content, pH value and the eightions. Finally, we studied the causes and variations of groundwater level andgroundwater salinity. This can be a scientific basis for the rational use of landresources, better understanding of the soil structure and function, reasonable use ofwater resources in irrigation, soil salinity control and improvement, and thus cancontribute to the eco-environmental stability protection in Weigan-Kuqa Oasis.This research paper draws the following main conclusions:1) The area and proportion of each landscape types acquired throughclassification and statistics on four different period of TM/ETM+images (1989,2001,2006and2011, respectively), using remote sensing and geographical informationsystem technology. On this basis, quantitative characteristics, spatio-temporaldistributions and variations of landscape types were analyzed by transfer matrix andLUCC analysis method. The results show that the study area landscape type haschanged significantly during each period. From1989to2011, area of non-saline land is maximum in landscape types in the study area, and has shown an increasing trend,has increased1497.126km²; Severe salinized land has a constant decrease with acumulative reduction area of1401.7km², is the fastest and largest reduction land type;There was little change with decreased area of39.653km²in the moderate and slightsaline land in the past22years, but with a big spatial variation; Area water and otherland type had a rising trend from1989to2001, and had a decreasing tendency in theperiod from2001to2011. The results of landscape pattern analysis show that, plaquereunion has increased in the study area, plaque type formed a good connection, thedegree of heterogeneity and complexity of landscapes has reduced, fragmentationdegree was gradually declined.2) The results from soil salinization and PH value grading and analysis show thatall soil samples from different time and soil layers are belong to the slightly alkalinesoil. According to salt content size, Soil salt content in study area showed a top-downvertical differentiation characteristic in the soil profile, indicating that the salt has astrong property of surface gathering. The analysis on spatial variation of soil saltcontent showed that the oasis soil salt content is less than the oasis periphery. Theresults from spatial and temporal variation analysis of soil surface salt content showedthat saline soils are mainly concentrated in the east and southeast of the study area,soils in the west and northwest are with low salt content. In general, from west andnorthwest side to east and southeast corner of study area, soil salt content increasesgradually. From the time scale, soil salt content in spring was greater than in fall, soilsalt content kept increasing.Saline soil classification results by the equivalent ratio of CL^－/(2SO₄^2-) in thesoil showed that during different sampling time, chloride-sulfate and sulfate soilswere in the first place in different soil layers in the depth of10-30cm and30-50cm;Sulfides in the soil profile showed a growing trend from top to bottom, while thechloride reduced from top to bottom. 3) The results of correlation analysis on soil characteristics indicates that there ishigh positive correlation between soil salinity, conductivity and mineralization degree;there is no significant correlation between pH value and water content, and betweensoil characteristics above (salinity, conductivity and mineralization degree),respectively; there is good positive correlation between topsoil salt content and Na⁺,Cl^-, SO₄^2-ions; There is also certain positive correlation between salt content andCa2+ion; In different sampling period, there is no correlation between salt content andHCO₃^-, because HCO₃^-is the performance of alkalization. There is an inverserelationship between alkalization and salinization process, and alkalization is closelyrelated to desalination. This illustrates that there is no desalination phenomenon in thestudy area.4) Analyzing results of groundwater depth and salinity data obtained from38monitoring well in the irrigation area during11-year period show that the spatialvariability of groundwater level in each spring larger than other seasons, reflecting thespring irrigation influence on groundwater level to a certain extent; It could beconcluded by analyzing Monthly average groundwater level changes and seasonalvariation of groundwater level, groundwater level in the study area reaches the top inspring, falls to minimum level in fall; The analysis on spatial and temporal changes ofgroundwater level showed that the overall average groundwater level of study areahas declining trend, while groundwater level is rising from upper part of irrigationarea to lower part or to fringe; groundwater of most of the monitoring wells werebrackish or salt water, and seasonal groundwater salinity were not changingsignificantly. The results from spatio-temporal variation analysis on groundwatersalinity in Irrigation area showed that groundwater salinity was decreasing during theperiod from1997to2007. Groundwater salinity was rising from upper part ofirrigation area to lower part or to periphery.