| The Three Gorges Reservoir area is located in the transition zone between the upper and middle reaches of the Yangtze River,with complex terrain and uneven seasonal distribution of precipitation Because of long-term deforestation,soil and water loss is serious and landslides and collapses occur frequently,making it one of the most vulnerable areas in China.Soil moisture is an important part of the earth’s surface hydrologic cycle,and its dynamic change is of great significance to vegetation restoration and reconstruction,efficient management of water resource and regional soil and water conservation.In this paper,the temporal and spatial changes of soil moisture were studied at different positions of typical hillslope in the Three Gorges mountainous area.Combined with field measurements and indoor physical and chemical properties experiments.,the temporal stability and main influencing factors were explored of soil moisture at different measuring locations(top,upper,middle,lower,toe and side slope positions)in a typical hillslope by using classical statistics and geostatistical analysis methods.The main conclusions are as follows:(1)The soil water content had obvious seasonal variation.The surplus period was from April to July,and the deficit period was from August to November.The average variation showed moderate variability.The variation of soil moisture decreased and thereafter increased with increasing soil depth.There is a significant correlation between the soil texture and soil moisture content.(2)At the vertical profile,soil moisture deficits were found at the 0-5 cm and 40-80 cm,while surplus existed at 5-40 cm.The standard deviation of the relative deviation of the sample positions are small at the bottom and upper slope positions,which were 1.49%and 1.97%respectively,therefore,they were able to represent the average value of soil moisture in the study area.While the standard deviation of the soil moisture was high at the lower position,reaching 12.87%,indicating that the temporal pattern was less stable.(3)The results showed that the soil moisture at all soil depths(0-5 cm,5-20 cm,20-40 cm,40-60 cm and 60-80 cm)had strong time stability,with the Spearman rank correlation values significantly correlated at P<0.05 level.Besides,the time similarity of spatial pattern of soil moisture was slightly higher in the wet season(mean Spearman’s coefficient 0.95)than dry season(mean Spearman’s coefficient 0.94).(4)Precipitation was the main controlling factor influencing soil moisture dynamic change.It had a significant impact at shallow soil layer,causing large fluctuations of soil moisture content,.While the rise and fall of soil moisture at deep soil layer was slow and the variation range was small.There are differences in the effects of rainfall events on soil moisture content among various rainfall classes.Saturated hydraulic conductivity was the most important factor affecting the temporal stability of soil moisture.In addition,vegetation cover and topographic slope position had influence on the temporal stability of soil moisture. |
