| Lop Nur playa looks like the ear of a human being on a gigantic scale from satellite images, at which numerous scientists and explorers marveled. A great deal of research programs had tried to unveil the mysteries of this grand ear, hence producing wealth of research fruits, while little about formation to rings of "Great Ear". Early experiments have clearly pointed out that it is hard to correlate the different colors of rings set with the corresponding salty-crust thickness, but it is known that the moisture in salty-crust whose color trend to dark is higher than those light color trend to white.According to the interpretation of the satellite images about saline soil, we know that the moisture content in an area of satellite images is higher, the hyper-spectral reflection is lower, and its color in this area is darker. Based on this foundation, the dissertation monitored the on-field salty soils of typical grey and dark stripes at two observing sites (OBS) within the playa area which like a Human Ear, Lop Nur. Two observing sites, one observing site in typical bright (tending to white) strips is named by WOS and another one in typical grey (tending to black) strips is called BOS within the Lop Nur playa. Key variables that may affect formation of stripes (i.e. meteorological, temperature and moisture of soil profiles, topsoil water content) were measured with the objectives of characterizing moisture in salty crust of different stripes. In addition, the research attempted to reveal the evolution and formation of Lop Nur form the point of view of moisture by incorporating groundwater table and topographic information. This research may provide the scientific basis for the evolution of environment and soil and water resources in Lop Nur or extreme arid areas.After one year monitoring, the results obtained showed that:1) Base on the field experiment, the mean value of adsorbed moisture in salty-crust at WOS was 61.5g kg-1, it was slightly higher than that of BOS, which was 60.9g kg-1. The mean value of crystal moisture at BOS was 34.3g kg-1, is apparently higher than those of WOS, which was only 7.3g kg-1. It could be hence concluded that adsorbed moisture of salt-crust in the two observing sites differed; the adsorbed moisture in the surface of salt-crust is higher than the crystal moisture. The difference of adsorbed moisture in the two observing sites is less than1.0g kg-1, and the content of crystal moisture at BOS is over 3 times higher than that at WOS, and the potassium ions in BOS is 2.4 times higher than that in WOS, at the same time, the magnesium ions in BOS is even 17.4 times higher than that in WOS. The results also revealed that the chemical composition of top salty crust of WOS and BOS was different, the varying chemical composition and mineral composition, may be the main contributor to the differences moisture in two OBS.2) The correlation analysis between the moisture in salty crust and potentially related factors (i.e. meteorological data, temperature and moisture of air within salty crust profiles, and salty crust temperature) suggested that the moisture change is almost independent of the change of groundwater table. A significant positive correlation was observed between adsorbed moisture at WOS/BOS and atmospheric humidity, and negative correlation with atmospheric temperature, daily evapotranspiration, and the temperature of the atmosphere observed respectively at salty-crust profile. It is the same as crystal moisture at WOS, while the correlation between crystal moisture at BOS and atmospheric temperature is negative. The correlation coefficients between the moisture and factors are of medium intensity. From the correlation analysis, it may be concluded that the dominant factor for the change of adsorption moisture is meteorological factors.3) The absorption capability of salt-crust at BOS is remarkably stronger than that at WOS both under high humidity which trending to increasing, and different temperature which trending to declining in field test in winter, the cumulative increasing of moisture in salt-crust at BOS is about 4% after 3 days, and that of the salt-crust in WOS are only increased by 0.6% throughout all the testing time.4) The absorption moisture experiment was simulated under the same relative humidity of 60% and various temperatures of 20℃,30℃ and 40℃, and the results show that the salt-crust in BOS express a stronger water absorption capability. The cumulative increasing of moisture in salt-crust at BOS is about 7% under simulating temperature after 22h. On the contrary, the salt-crust in WOS does show weak water absorption capability in the experiment process, the moisture content are only increased by 0.5% at all the testing time. The absorption capability of salt-crust in BOS is remarkably stronger than that in WOS under any simulated temperature.5) The silt-clay layer is 60cm-depth below the surface in salty crust. The mean to adsorbed moisture in silt clay at WOS was 203.5g kg-1, it was higher than that of BOS, which was 144.8g kg-1. The mean value of crystal moisture in silt clay at WOS was 16.1g kg-1, and the mean value of crystal moisture in silt clay at BOS was 15.2g kg-1. The correlation analysis between the moisture in salty crust and potentially related factors such as the moisture in the silty clay layer, the temperature and moisture of air within silty clay profiles, and silty clay temperature, were conducted and the results showed that the moisture change in salty crust is almost independent of the change of air temperature & humidity in the silty clay layer.Base on the experiment in Lop Nur playa, the moisture changing of top salt-crust is directly related with the meteorological factors, and that is rarely affected by others factors, such as the change of groundwater table and the change of temperature and humidity in salt-crust profile. According to the adoption moisture ability of salty crust and the spectrum reflection about saline soil, the long-term difference of color to the rings of "Great Ear" in Lop Nur playa is mainly caused by the difference of crystal moisture in top salty crust, and the short-term difference of color is mainly caused by the difference of absorption moisture. The varying chemical composition and mineral composition, whose potassium ions and magnesium ions in top salty crust are remarkably different, and the potash mineral at BOS, which highly moisture-absorbing, is much richer than that at WOS, may be the main contributor to the differences moisture in two OBS. This research can reveal the long-term "Great Ear" profile and the short-term shading of the color in Lop Nur playa on the remote sensing image, and this study can also provide theoretical foundations for environmental change research about playa in arid zone and prospecting minerals through the remote sensing technology. |
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