| The uneven distributions of temporal variation in precipitation, the highly evolution of karst conduit and fractures in subterrane karst result in a series of ecology environment problems that are susceptible to cause serious seasonal and engineering water storage in Southwest China. Epikarst water becomes the main or even only water resource for desertification treatment and local resident domestic water in karst rocky mountainous area. Vegetation-soil-epikarst generally is seen as integrate system to evaluate the regulation function. However, the soil regulation capacity is difficult to determined due to the thin soil and inhomogeneous distribution in karst regions. The facts have demonstrate that water resource is abundant and the dynamic variation is stable where the extent of soil covering and vegetation growth well. Monitoring of the profile of soil moisture through manual sampling and situ automatic recording had been conducted to analyse the dynamic variations of soil moisture content, and to quantitatively evaluate soil regulation capacity in Yaji experimental site of Guilin city, Southwest China. Therefore, understanding the characteristics of soil moisture has significant implications for studing the transport mechanisms of soil moisture and formulating reasonable management practices for rocky desertification.The results of soil physicochemical properties for six soil sampling points on Yaji hillslope show that soil quality is good after about 30 years natural recovery. The soil environment is suitable for most plants growth. Slope is negative correlation with organic content but positive correlation with soil bulk density and clay content with exception of saddle area.Soil mass water content displays an increased tend with the depth. The rapid change layer, steady layer, sub-rapid change layer and upswing layer have been determined by the variation rate of soil moisture. Moreover, soil stratification for volumetric water content gained from automatic record data also can be divided into speedy changing layer, active layer, speedy changing layer and relatively stable layer on the basis of the standard deviation. Soil thickness plays an important role in determining the stratification results. The critical depth for soil moisture variation is approximately 30 cm. The lower soil layer has the more regulation capacity, characteristed by the stable dynamic variation of soil moisture.The response of soil moisture to typical precipitation events had been selected to analyse the dynamic characteristics from one year hydrological mointoring. The results show that:(1) The response process of soil moisture to rainfall is sensitive and rapid. Responsing time is about 0.5~3.5 h that associates with rainfall intensity, duration and total precipitation amount. The response threshold is 9 mm in dry season as a function of excessing the prior soil moisture deficit. The “full storage” phenomenon often is observed for 90 cm and 140 cm soil moisture after heavy rainfalls. The durations of peak value are 8~10 h, 10~12 h respectively. This is closely related to soil moisture saturation condition for lower lays, probably, resulted in the generation of surface overflow.(2) In generally, recession rate of soil moisture is lower than response rate, which decreases with the increase of soil depth. The decline curve of 20 cm, 40 cm soil water becomes moderate after 30 h of precipitation. The 90 cm soil moisture maintains at 27% in dry season, 26% in rainy season. The diurnal variation of soil moinsture at the late stage of recession curve can be observed. The occurence time of maximum value is at 22-24 hour, while with the minimum soil moisture at 16-18 hour.(3) The maximum water storage capacity of monitoring site is 532.23 mm, with the magnitude of 242.55 mm. The percolation flow maybe source from the middle and lower soil layer, which plays a significant role in plant water requirement in dry season, epikarst and cave dripwater. The thicker soil layer, the more regulation capacity. |
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