Soil salinization is a common phenomenon that affects both the environment and the socio-economy in arid and semi-arid regions; it is also an important aspect of land cover change. In this study, we integrated multi-s...Soil salinization is a common phenomenon that affects both the environment and the socio-economy in arid and semi-arid regions; it is also an important aspect of land cover change. In this study, we integrated multi-sensor remote sensing data with a field survey to analyze processes of soil salinization in a semi-arid area in China from 1979 to 2009. Generally, the area of salt-affected soils increased by 0.28% per year with remarkable acceleration from 1999 to 2009 （0.42% increase per year）. In contrast, the area of surface water bodies showed a decreasing trend （-0.08% per year） in the same period. Decreases in precipitation and increases in aridity due to annual （especially summer） warming provided a favorable condition for soil salinization. The relatively flat terrain favored waterlogging at the surface, and continuous drought facilitated upward movement of soil water and accumulation of surface saline and calcium. Meanwhile, land-use practices also played a crucial role in accelerating soil salinization. The conversion to cropland from natural vegetation greatly increased the demand for groundwater irrigation and aggravated the process of soil salinization. Furthermore, there are potential feedbacks of soil salinization to regional climate. The salinization of soils can limit the efficiency of plant water use as well as photosynthesis; therefore, it reduces the amount of carbon sequestrated by terrestrial ecosystem. Soil salinization also reduces the absorbed solar radiation by increasing land surface albedo. Such conversions of land cover significantly change the energy and water balance between land and atmosphere.展开更多
The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thaw...The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thawing experiment was conducted with Lanzhou loess(LZL)and Qinghai-Tibet Plateau silty clay(QSC)using a novel layered nuclear magnetic resonance approach.During LZL freezing,the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front,but decreased with decreasing temperature in other layers,whereas during the freezing of QSC,the unfrozen water content in different layers(including the freezing front)decreased with decreased temperature.Notably,the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water.In addition to the temperature gradient,the squeezing action during soil freezing was another important factor affecting water migration,especially at the early stage of soil freezing.However,which of the two factors,squeezing action and temperature gradient,was the dominant one causing water migration depended on soil structure.At the early stage of soil freezing,the squeezing action had a significant effect on the water migration of LZL,but no significant effect on that of QSC.Furthermore,water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice.This study provided an improved understanding for ice segregation and water migration during soil freezing.展开更多
基金supported by the National Basic Research Program of China (Grant No.2009CB723904)the National Natural Science Foundation of China (Grant No. 41105076)+1 种基金the National Key technology R & D program (Grant No. 2012BAC22B04)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA05090201)
文摘Soil salinization is a common phenomenon that affects both the environment and the socio-economy in arid and semi-arid regions; it is also an important aspect of land cover change. In this study, we integrated multi-sensor remote sensing data with a field survey to analyze processes of soil salinization in a semi-arid area in China from 1979 to 2009. Generally, the area of salt-affected soils increased by 0.28% per year with remarkable acceleration from 1999 to 2009 （0.42% increase per year）. In contrast, the area of surface water bodies showed a decreasing trend （-0.08% per year） in the same period. Decreases in precipitation and increases in aridity due to annual （especially summer） warming provided a favorable condition for soil salinization. The relatively flat terrain favored waterlogging at the surface, and continuous drought facilitated upward movement of soil water and accumulation of surface saline and calcium. Meanwhile, land-use practices also played a crucial role in accelerating soil salinization. The conversion to cropland from natural vegetation greatly increased the demand for groundwater irrigation and aggravated the process of soil salinization. Furthermore, there are potential feedbacks of soil salinization to regional climate. The salinization of soils can limit the efficiency of plant water use as well as photosynthesis; therefore, it reduces the amount of carbon sequestrated by terrestrial ecosystem. Soil salinization also reduces the absorbed solar radiation by increasing land surface albedo. Such conversions of land cover significantly change the energy and water balance between land and atmosphere.
基金supported by the Key Project of the Natural Science Foundation of China(No.41630636)the National Natural Science Foundation of China(No.41501072)+1 种基金the Independent Foundation of State Key Laboratory of Frozen Soil Engineering,China(No.SKLFSE-ZT-202107)the Natural Science Foundation of Gansu,China(No.22JR5RA057).
文摘The formation and growth of segregation ice dominate the frost heave during soil freezing,which is closely related to water migration.To analyze segregation ice during soil freezing for different soils,a freezing-thawing experiment was conducted with Lanzhou loess(LZL)and Qinghai-Tibet Plateau silty clay(QSC)using a novel layered nuclear magnetic resonance approach.During LZL freezing,the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front,but decreased with decreasing temperature in other layers,whereas during the freezing of QSC,the unfrozen water content in different layers(including the freezing front)decreased with decreased temperature.Notably,the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water.In addition to the temperature gradient,the squeezing action during soil freezing was another important factor affecting water migration,especially at the early stage of soil freezing.However,which of the two factors,squeezing action and temperature gradient,was the dominant one causing water migration depended on soil structure.At the early stage of soil freezing,the squeezing action had a significant effect on the water migration of LZL,but no significant effect on that of QSC.Furthermore,water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice.This study provided an improved understanding for ice segregation and water migration during soil freezing.
