干旱区重度和轻度盐碱地包气带水分运移规律

为揭示干旱区不同灌溉模式下的包气带水分运移规律,该研究综合使用原位观测、同位素示踪和数值模拟等方法,对跨流域调水背景下,克拉玛依农业开发区重度和轻度盐碱地棉田的土壤水势、土壤含水率和土壤水同位素组成特征,包气带水量平衡以及水分运移规律进行了研究。研究表明,土壤基质势调控的滴灌模式下,重度和轻度盐碱地的灌溉入渗主要影响深度是地表以下0~150 cm,土壤含水率和土壤水势对灌溉和蒸散发动态变化的响应明显,具有前期土壤水和观测期内灌溉入渗水的混合特征。深层(重度盐碱地150~260 cm;轻度盐碱地250~350 cm)受地下水毛细作用影响,土壤水势和土壤含水率对地下水埋深动态变化的响应明显,具有前期土壤水与地下水的混合特征。轻度盐碱地中间层(150~250 cm),几乎不受灌溉入渗和地下水毛细作用的影响,土壤水势和土壤含水率处于动态平衡,主要为前期土壤水的特征。HYDRUS-1D数值模拟结果表明,深层土壤水与地下水之间存在双向交换,地下水对土壤水以补给作用为主,重度和轻度盐碱地地下水补给占包气带水分来源的比例分别为7.9%和15.0%。该灌溉模式对农业开发区地下水补给有一定的抑制作用,但观测期内区域地下水位抬升幅度在50~60 cm之间,说明存在一定的土壤次生盐渍化和地下水咸化的潜在风险。

Water movement law through unsaturated zone in severe and mild saline-alkali fields in arid region

Abstract: To investigate water movement through the unsaturated zone under different kinds of irrigation modes can provide scientific basis for decreasing dryland salinity in arid area. Most researches focused on controlling water and salt conditions of the topsoil or creating a suitable environment within the root zone for plants growth. However, there are few studies on the mechanism of soil water movement in the unsaturated zone under drip irrigation and its impacts on groundwater recharge, or the relationship between soil water and groundwater. In this study, we analyzed water movement through the unsaturated zone in severe (Plot 1) and mild (Plot 2) saline-alkali cotton fields of the Karamay Agricultural Development Area (KADA) accompanied by interbasin water transfer, based on in-situ observation, stable isotopes tracing, and numerical simulation. The results show that under matric potential controlled drip irrigation, infiltration depths are about 0-150 cm for both plots, and the dynamics of soil water content (SWC) and soil water potential (SWP) show the responses to irrigation and evapotranspiration. Soil water in this layer is the mixture of antecedent soil water and irrigation water during the observation. The depths of 150-260 cm for Plot 1 and 250-350 cm for Plot 2 are affected by capillary upflow from groundwater, and the dynamics of the SWC and SWP vary with the water table depth. Soil water in these depths is the mixture of the antecedent water and groundwater. There is a middle layer (150-250 cm) in Plot 2, neither affected by infiltration nor groundwater capillary rise, along with dynamic balance of SWC and SWP. And soil water in this layer is dominated by the antecedent water. According to HYDRUS-1D modelling results, for Plot 1, irrigation (precipitation) and groundwater respectively account for 92.1% and 7.9% of the sources of the unsaturated zone, while evapotranspiration and soil water storage increase account for 64.3% and 35.7% of the sinks of the unsaturated zone, respectively. For Plot 2, irrigation (precipitation) and groundwater account for 85.0% and 15.0% of the sources of the unsaturated zone, respectively, while evapotranspiration and soil water storage increase account for 92.4% and 7.6% of the sinks of the unsaturated zone, respectively. The ratio difference at these 2 plots is caused by higher irrigation amount along with higher matric potential control level at Plot 1. There is a two-way exchange between deep soil water and groundwater, and groundwater recharges soil water in general. The current drip irrigation mode in the cotton fields can be conductive to salt leaching out of the main root zone, i.e., within the 60 cm depth below ground surface in this area. Plot 2 was less prone to secondary salinization in comparison with Plot 1 due to the middle layer extending the distance between the root zone and groundwater. However, the water table rise of about 50-60 cm during the observation period implies the potential risk of secondary soil salinization and groundwater salinization. To prevent above phenomena, enhancing water-saving irrigation and improving current drainage systems are in urgent need.