切沟中土壤水分的空间变化特征

切沟侵蚀不仅破坏土地资源，而且影响下游地区环境。目前的土壤侵蚀预报模型没有包括切沟侵蚀，因此研究切沟中土壤水分空间变化是建立切沟侵蚀模型的基础，也是恢复植被的基础。在陕西省安塞大南沟流域选择一个切沟，从1998-2000年连续 3年在 4～10月间对切沟不同部位土壤水分状况进行了观测。分析结果表明，切沟中浅层土壤水分空间分异规律明显，沟顶土壤水分状况较好，土壤容积湿度达到10．3％。沟坡则较差，但沿沟坡向下到沟底，土壤水分不断增加，分别为 6．3％、6．4％和10．4％。沟坡陡崖的土壤水分条件最差，接近凋萎湿度，容积含水量仅为4.6％～5.9％。沟底土壤湿度有所好转，为 7．7％。从雨季开始到结束，整体上土壤水分呈下降趋势，但随降雨事件发生波动。季节变化比较明显的是土壤水分条件好的部位，如沟顶、沟坡底部和沟底。尤以沟底变化最大。沟坡陡崖土壤湿度随季节没有任何变化。从1998-2000年，随降水量减少，切沟所有部位土壤湿度持续下降，即使在水分条件较好的沟顶和沟坡下部，土壤湿度也仅为 8．1％～8．8％，其它部位则都接近于凋萎湿度。土壤水分亏缺相当严重。切沟不同部位土壤水分的季节和年际变化主要受降雨入渗补给影响，而沟底则与径流的产生有关。因此应进一步研究不同降雨类型与径流产生、以及土壤湿度变化的关系。

SPATIAL DISTRIBUTION OF SOIL MOISTURES IN A GULLY WATERSHED

Gully erosion damages land resources and causes site-off environmental problems.  But little gully erosion model included in soil erosion models.  It is necessary to study soil moistures in a gully watershed for establishing a gully erosion model and restoring vegetation.  A gully watershed was selected in Ansai County, Shaanxi Province to study soil moisture spatial distribution and its seasonal and annual variations.  From 1998 to 2000, soil moistures were measured every April to October by using TDR systems installed in different gully positions.  The analyzed results showed that there were obvious different soil moistures in a gully watershed.  The higher water content was in the gully top which was 10.3% of volume.  Soil water was poorer in gully sides and increased from upper slope to lower slope, which were 6.3%, 6.4% and 10.4% respectively.  For gully cliff, soil moisture was close to wilting point, which was the driest soil in a gully watershed.  Gully floor had relative higher soil moisture of 7.7%.  During the rainfall season from April to October, soil moistures decreased in the whole gully system, but there were fluctuations corresponding to the occurrence of rainfall events.  The higher the soil moistures were, the higher the seasonal variations were.  Soil water content in the gully floor had the largest varied range of 10.3% during the rainfall season.  But soil moistures in gully cliff had no any change during the season, even during 3 years.  From 1998 to 2000, soil moistures of all the positions in the gully watershed reduced continually.  Gully top and lower slope only had 8.1%~8.8% of soil water and other locations were near to wilting point.  The spatial distributions and seasonal or annual variations of soil moistures in different potions of a gully watershed depends on rainfall supply largely.  For the gully floor, soil water content was influenced by the runoff generation besides rainfall supply.  It would be valuable to further study the relationship between rainfall types and runoff generation and soil moisture variations.