黄土区小流域植被类型对沟坡地土壤水分循环的影响

沟坡作为黄土丘陵区小流域水土流失最为活跃的区域,探究不同下垫面植被类型下的土壤水分循环特征对于沟坡地植被恢复具有重要意义。基于氢氧同位素示踪技术,通过野外水样采集和室内同位素分析旨在揭示植被类型对沟坡地土壤水分循环的影响机制。结果表明:(1)各水体氢氧同位素均遵循:降水刺槐林地土壤水草地土壤水地表水地下水,降水的变异系数最大,地表水和地下水的变异系数较小。(2)草地土壤水主要以降水补给为主,所占比例为59.12%,刺槐林地土壤水则以深层土壤水的上升补给为主,所占比例为60.97%。短阵性暴雨条件下,草地土壤水运移速率较刺槐林地高约1 cm/d,且主要发生在0—50 cm土层。(3)土壤水的垂向运移为地下水的主要补给形式,草地土壤水对地下水的补给比例为51.64%,约比刺槐林地高0.52%。表明植被类型对土壤水分循环特征具有一定的影响,刺槐林对深层土壤水分利用强度较大,可能加剧深层土壤干层化,而草地更有利于降水入渗以及地下水补给,该研究可为小流域沟坡的生态修复和综合治理提供科学依据。

Effects of vegetation types in small watershed on soil water cycle in gully-slope land of loess region

The gully-slope land is the most active area of soil erosion in small watershed of loess hilly region. It is of great significance to explore the characteristics of soil water cycle under different underlying vegetation types for vegetation restoration on gully-slope land. Based on the hydrogen and oxygen isotope tracer technique, the mechanism of vegetation types affecting soil water cycle in gully-slope land was revealed through field water sample collection and indoor isotope analysis. The results were: (1) The hydrogen and oxygen isotope concentration in the five water bodies decreased in an orderly way, with precipitation being observed to have the greatest amount, followed by soil water of black locust forest, then soil water of grassland, then surface water, finally groundwater. The coefficient of variation of precipitation was the largest, and the coefficient of variation of surface water and groundwater was smaller. (2) Soil water in grassland was mainly recharged by precipitation, accounting for 59.12%. Soil water in black locust forest was mainly recharged by the rising of deep soil water, accounting for 60.97%. Under the condition of short-burst rainstorm, the water transport rate of grassland soil was about 1 cm/d higher than that of black locust forest. And the main transport ranges of soil water in two vegetation types were 0-50 cm. (3) The vertical migration of soil water was the main form of groundwater recharge. The groundwater recharge ratio by soil water of grassland was 51.64%, which was about 0.52% higher than that of black locust forest. It indicated that the vegetation type had certain influence on the characteristic of soil water cycle. Black locust forest had a strong utilization of deep soil water, which might aggravate the dried soil layer of deep soil. And the grassland was more conducive to precipitation infiltration and groundwater recharge. This study can provide a scientific basis for ecological restoration and comprehensive management of gully-slope land in small watershed.