水盐动态与土地利用变化相互作用的分析

Interaction of Land Use Change and Spatial and Temporal Dynamics of Soil Moisture and Salinity in Arid Land

利用1987年和1998年两期土地利用现状图,1988～1998年水文资料和2000年、2001年地下水和土壤水、盐含量的监测资料,分析三工河流域水盐的时空动态变化对流域土地利用的影响.1988～1998年三条河流年出山口总径流量10年间无显著变化,但上游老绿洲耕地面积逐步扩大,引水量逐年增加,可以占到出山口径流总量的90%以上.1998年相对于1988年,上游绿洲地下水位有所下降,而所有下游观测点的地下水位均有所升高,盐渍化问题加剧.通过2000年和2001年三工河流域下游的新垦绿洲地下水、土壤的连续观测表明,从绿洲、过渡带到沙漠中,土壤盐分含量的变化梯度不大,差异不显著,而水分则有显著的下降趋势.但是在过渡带由于受绿洲灌溉过程的影响,地下水位较浅,土壤含水量较高,植被较为稳定,因此绿洲边界始终没有变化.因此水分的减少是绿洲过渡带动态稳定的关键限制因子.绿洲内的撂荒地和靠近绿洲的荒漠草地受绿洲内部灌溉过程的影响,地下水位升高,超过了地下水的临界深度,同时又因为缺少灌溉的反复淋洗,在强烈的蒸发作用下,盐分的表聚现象十分明显,而且整个剖面内盐分的含量都较高,土壤的盐渍化现象非常严重.

In 2000 and 2001, the water content and salinity of soil, groundwater table and salt concentration were investigated in Sangonghe basin. Using the land use maps of 1987 and 1998, the dynamics of land use and the influence of spatio-temporal dynamics of water and salinity on land use are analyzed. In old oasis of the upper reaches of the rivers, farmland area increased gradually, and water used in old oasis also increased, acccounting for over 90% of the total runoff. Compared with 1988, 1998 witnessed a drop of groundwater table in old oasis but a rise in all investigation spots of new oasis in the lower reaches. In the new oasis of lower reaches of Songonghe, from oasis, ecotone to sand dune, soil salinity has not changed much, and no significant differences among these ecosystems have been found. Soil water content has decreased much from oasis, ecotone to sand dune. In ecotone, influenced by irrigation of the adjoining oasis, groundwater table has been raised and soil water content also increased compared with sand dune nearby, vegetation developed well, ecotone has been very stable and border of oasis has not changed for decades. From oasis to abandoned land and desert grassland, soil salinity changes much with significant difference in spatial variations. In abandoned land and peripheral desert of oasis, influenced by irrigation of oasis, groundwater table has been raised above the critical depth.Because the soil salt cannot be eluviated by irrigation water and precipitation, salt brought to the upper layers of soils by strong evaporation is especially concentrated on soil surface.