格尔木河流域平原区植被对地下水依赖程度评价

Evaluation of groundwater dependent vegetation in the plain area of the Golmud River catchment

关键词:  依赖地下水植被  地下水  GIS  格尔木河流域

Key words:  groundwater dependent vegetation (GDV)  groundwater  GIS  Golmud River catchment

摘要:

格尔木河流域平原区植被生态高度依赖地下水。为了评价格尔木河流域平原区植被对地下水的依赖程度,在野外调查的基础上,文章基于遥感解译与GIS空间分析技术,构建包含蒸散发、植被覆盖度、地下水埋深、地下水溶解性总固体、土壤含盐量和土壤含水率的评价指标体系,采用主成分分析法确定各指标权重,结合空间叠加技术得到植被依赖地下水指数。结果表明: (1) 土壤含水率权重27.36%、植被覆盖度权重26.34%,为评价体系核心指标;蒸散发权重21.68%、地下水埋深权重12.95%,对依赖程度空间分异具有显著控制作用;(2) 植被依赖地下水程度由“非常低”到“非常高”面积占比依次为54.34%、8.90%、28.22%、8.21%、0.33%;(3) 山前戈壁砾石带与北部盐沼带植被依赖地下水程度为“非常低”等级,“高”及“非常高”区域主要集中在山前冲洪积扇溢出带轴部,依赖等级整体呈现由东南向西北方向逐渐降低的趋势。经地表水关联性分析和水位埋深阈值法合理性验证分析,评价结果可靠。研究成果可为格尔木河流域地下水与植被协同管理提供依据,并为类似区域依赖地下水植被生态评价提供方法参考。

Abstract:

Background, aim, and scope Groundwater serves as a decisive factor for vegetation survival in arid regions. The plain area of the Golmud River catchment in northeastern Qaidam Basin has a fragile ecological environment, and local vegetation is highly dependent on groundwater. This study aims to quantitatively assess the degree and spatial pattern of vegetation dependence on groundwater. Combined with field surveys, remote sensing inversion and GIS spatial analysis, a multi-index evaluation system is constructed to establish a vegetation dependence on groundwater index (VI). The research results provide scientific support for the coordinated management of groundwater and vegetation as well as ecological protection in arid areas. Materials and methods This study area is located in the Golmud River catchment, which covers a total area of 33712.12 km². The watershed exhibits a characteristic mountain-basin geomorphic pattern. An evaluation system was constructed using six indicators: evapotranspiration (ET), fractional vegetation cover (FVC), soil water content (SWC), soil salt content (SSC), water table depth (WTD), and total dissolved solids (TDS). Principal component analysis was used to assign weights, and an overlay analysis based on GIS was applied to calculate and grade the VI. Results Principal component analysis results indicate that the weights of ET, FVC, SWC, SSC, WTD, and TDS content in the evaluation system are 21.68%, 26.34%, 27.36%, 9.51%, 12.95%, and 2.16%, respectively. The final evaluation results show that the area percentages of vegetation dependency levels across the plain from "very low" to "very high" are 54.34%, 8.90%, 28.22%, 8.21%, and 0.33%, respectively. Spatially, very low dependency areas are mainly distributed in the piedmont gobi gravel zone and salt marsh, while high and very high dependency areas are concentrated along the frontal edges of the alluvial fans. Analysis of surface water connectivity reveals that as the distance from the river channel increases, the proportion of very high and high dependency areas gradually decreases, while the proportion of low and very low dependency areas progressively increases. Validation based on the groundwater depth threshold indicates that 94.87% of the sampling points in high and very high dependency zones have a water table depth of less than 3 m, which is consistent with existing research findings in the study area. Discussion The findings align with established ecohydrological principles. The identification of SWC and FVC as the primary drivers is logical; SWC represents the immediate water source available to plant roots, heavily influenced by capillary rise from shallow groundwater in this arid environment, while FVC reflects the integrated health and response of the ecosystem to water availability. The concentration of high dependency vegetation in groundwater discharge areas is a classic hydrological behavior, creating ecological refugia that are particularly vulnerable to groundwater drawdown. The validity of the assessment was confirmed through two independent verification methods. First, a buffer analysis along river channels showed a clear distance decay effect, where the proportion of medium to high dependency vegetation decreased significantly with increasing distance from the river, confirming the role of surface water and groundwater exchange. Second, a groundwater depth threshold validation demonstrated that 94.87% of the survey points located in high and very high dependency zones had a water table depth of less than 3 m, which is consistent with previously established ecological thresholds for the research area. This strong agreement confirms the credibility and robustness of the proposed evaluation framework. Conclusions The dependence of vegetation on groundwater in the Golmud River catchment plain area exhibits a distinct spatial pattern: low dependence in the northern and southern zones and high dependence along the central corridor. Areas with very low dependence, covering the largest extent, are primarily located in the piedmont gobi gravel zone and the salt marsh. In contrast, zones of high and very high dependence are concentrated along the frontal edges of the alluvial fans. This distribution is closely linked to the surface water and groundwater interaction. Areas of moderate dependence show a transitional pattern, reflecting the gradient change in vegetation sensitivity to groundwater under varying hydrogeological conditions. Principal component analysis reveals that SWC and FVC are the most significant influencing factors. SWC directly indicates the capillary rise of groundwater, while FVC represents the integrated biological response. ET and WTD indirectly influence dependence by regulating soil water availability. The weights of each indicator are highly consistent with the hydrogeological and eco-environmental characteristics of the study area, distinctly reflecting the differentiated contribution of each factor to vegetation groundwater dependency. Recommendations and perspectives Groundwater dependent vegetation ecosystems exhibit significant dynamic characteristics. In the future, it is essential to integrate climate change scenarios and dynamic monitoring data into the evaluation model to enhance its predictive capability and applicability, thereby providing more reliable decision-making support for the synergistic management of groundwater and vegetation systems and ecological conservation.