Characterization of Soil Environmental Changes in Northern Tarim Basin in China

Spatio-Temporal Variation Analyses of Salinized Soils Derived from Satellite Data

Abstract

Leakages from the soil waterway, improper irrigation, and incomplete drain system have raised the groundwater levels in arid areas and caused salinization, i.e. accumulation of salts in the top soils. Vulnerability of salinization is also controlled by topographic properties and soil conditions. This study focuses on a desert area in the northern Tarim Basin, northwest China, because the rapid progress of salinization has been reported. One main factor for the salinization in the study area is the excessive water supply in the agriculture lands. For clarifying the salinization process, 40 scenes of satellite imagery in total by Landsat T‚l/ETM+ (acquisition years: 1990 and 2000) and Terra/ASTER (acquisition years: 2003, 2004, and 2006) were selected. Three normalized difference indices on vegetation, soil, and water and a color composition of the indices were adopted to detect surface changes in the period from 1990 to 2006. As a result, the salinized soils were found to have extended in the downstream, and their area increased monotonously with the time while the area of fixed dunes decreased largely. We proposed a Salinity Index to extract correctly the salinized areas from the ASTER images by refereeing to the reflectance spectra of the soil samples. This Salinity Index clarified that the salinized soils have high salt concentrations over 30 ppt and the concentrations of the moving sands are also high. In addition, the high salinity accumulation in the downstream of farmlands was identified, which implied a strong effect of agricultural development on the salinization.