浅地下水埋深微域尺度苏打盐渍土的积盐机理探讨

MECHANISM OF SALT-ACCUMULATION IN MICRO-SCALE SODIC SALINE SOIL AS AFFECTED BY SHALLOW GROUNDWATER TABLE

通过野外定位观测和室内化验,探讨了浅埋地下水环境下苏打盐渍土的积盐机理。结果表明:在35×35m2大小的区域内,相对高差仅60cm,包括盐化草甸土、浅位柱状碱土、白盖苏打碱土和中位柱状碱土4种土壤类型。盐化草甸土分布在相对较低的洼地,几乎没有碱化层;白盖苏打碱土和中位柱状碱土分布在微坡地和高平地。高平地土壤的碱化层出现在15～30cm,碱化度(ESP)70%,微坡地土壤的ESP表层最大达75%。地下水位(初见水位)表现为洼地凸出的三维空间格局,洼地和高平地之间的地下水初见水位差达1m以上,24h后的水位基本保持在同一水平。地下水位在冻结期的变化与冻土的形成和发展有一定相关性。冻结期,部分浅埋地下水进入冻层,导致冻层含水率增加,同期地下水开始缓慢下降。盐化草甸土表层的含水率从冻结前的20%增加到50%(过饱和状态),其增量达到显著性水平(p<0·05);苏打碱土冻结层含水率有一定的变化,但变化程度不显著。冻融期间,苏打碱土表层含盐量迅速增加,其中白盖苏打碱土表层含盐量增量幅度达80%,而盐化草甸土表层的盐分含量变化不显著。

Based on insitu observation and analysis in laboratory, mechanism of saltaccumulation in sodic saline under shallow groundwater level was explored Results show that within the study plot, 35×35m2 in area, varying only 60 cm in altitude, existed four types of soils i.e. sodic saline meadow soil, shallow columnar sodic alkaline soil, white crust sodic alkaline soil and median-columnar sodic alkaline soil. Sodic saline meadow soil was distributed in depressons, and almost free of alkaline layer; white crust alkaline soil and mediancolumnar sodic alkaline soils on micro slopes and high flatland. An alkaline layer was found in 15~30 cm in depth in high flatland, with ESP （exchangeable sodium percent） being 70%. On micro slopes, ESP of soil in the surface layer was the highest, up to 75%. Groundwater table （initial level） demonstrated a three-dimension pattern, being concave in depression, thus forming a difference of 1 m in water table between depression and high flatland, which was basically leveled off within 24 hours. Variation of groundwater table in the freezing period was found to be somewhat related to formation and development of frozen soil. Groundwater table was gradually lowered during the freezing period, as a result of some groundwater moving into the frozen layer, leading to a higher moisture content therein. Soil moisture content in the surface layer of saline meadow soil increased from 20% up to 50% （over-saturated）, during the period, demonstrating a significant increasing rate （p〈0.05）, however, it did not change much in the frozen layer of sodic alkaline soil. In the thawing period, salinity content in the surface layer of sodic alkaline soil increased quickly, especially in white crust sodic alkaline soil, by about 80%, whereas insignificant change was observed in the surface layer of saline meadow soil.