土地利用变化对土壤水补给来源影响研究

Impacts of land use change on sources of soil water recharge

为探究不同植被类型深剖面土壤水补给来源,以黄土区长武塬为研究区,采集两种土地利用方式(农地、18 a苹果园、26 a苹果园)下20 m深土壤剖面,测定土壤水及其稳定性和放射性同位素含量,基于同位素方法对不同土地利用类型下不同深度土壤水来源进行溯源分析。研究表明:(1)苹果园土壤水含量明显低于农地,说明果园耗水强度更大,对深层土壤水影响更为显著。(2)农地、18 a和26 a苹果园下降水偏移量分别为-22‰、-20‰和-6‰,说明降水补给土壤水后受到蒸发作用影响,且农地土壤水比果园受到的蒸发效应更强。(3)该区土壤水补给主要以活塞流为主;对于补给不同深度土壤的可能水源,6 m以下补给水的同位素组成(δ^(2)H=-83.8‰,δ^(18)O=-12.1‰)较0~6 m(δ^(2)H=-68.8‰,δ^(18)O=-10.1‰)更为贫化,且6 m以下补给水的氢氧稳定同位素组成与日降水量≥50 mm·d-1的降水更相似。与农地(δ^(2)H=-70.6‰,δ^(18)O=-10.4‰)相比,果园土壤补给水的氢氧稳定同位素组成(δ^(2)H=-76.1‰,δ^(18)O=-11.1‰)更贫化。综上,深层和果园土壤可能需要更高强度降水的补给,本研究对深厚非饱和带水循环过程的理解及水资源管理具有重要意义。

To explore the deep soil water recharge sources under different vegetation,the Changwu Loess Tableland was chosen as the study area,and soil samples from the surface down to 20 m under two land use types(farmland,18-year apple orchard and 26-year apple orchard)were collected and then the contents of soil water,stable(δ^(2)H andδ^(18)O)and radioactive(3 H)isotopes were measured.Based on the isotopic method,the source of soil water at different depths under different land use types was traced.The results showed that(1)Soil water content under apple orchards was significantly lower than that of farmland,indicating that orchards consumed water more intensely and had a significant impact on deep soil water.(2)The precipitation offset values were-22‰,-20‰and-6‰under farmland,18-year and 26-year apple orchards,respectively,indicating that soil water was affected by evaporation after the rainfall recharge.Specifically,orchards had lower evaporation effects.(3)Soil water movement in this area was predominantly via piston flow.For the possible soil water source at different depths,the isotopic composition of the recharge water below 6 m(δ^(2)H=-83.8‰,δ^(18)O=-12.1‰)was more depleted than that of 0~6 m(δ^(2)H=-68.8‰,δ^(18)O=-10.1‰),and the hydrogen and oxygen stable isotope composition of the recharge water below 6 m and the precipitation intensities≥50 mm·d-1 were very similar.Compared with farmland(δ^(2)H=-70.6‰,δ^(18)O=-10.4‰),the hydrogen and oxygen stable isotope composition of orchard soil water(δ^(2)H=-76.1‰,δ^(18)O=-11.1‰)was more depleted.These results suggested that deep and orchard soil water was recharged by higher-intensity precipitation and had important implications for the understanding of water cycle process and water resource management in deep unsaturated zones.