Spatial heterogeneity characteristics of soil-epikarst thickness in a typical karst dolomite small watershed
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摘要:
土壤-表层岩溶带厚度是喀斯特地球关键带的关键指标,明确其空间异质性特征对于理解地球关键带结构演化机理以及评估水源涵养功能具有重要意义。在广西环江木连小流域1.4 km2范围内,通过高密度电法(ERT)探测45条样线,共获取1 731个样点的土壤-表层岩溶带厚度及环境因子数据资料,研究了土壤和表层岩溶带厚度的空间分布格局及其影响因素。结果表明,土壤和表层岩溶带厚度平均值分别为1.15 m和6.44 m,且分别呈现强变异程度和中等变异程度。地统计分析结果表明球状模型和指数模型分别可以反映土壤和表层岩溶带的空间结构特征。土壤厚度呈现中等空间自相关性,变程长,空间连续性好;而表层岩溶带呈现强烈的空间自相关性,变程短,空间依赖性强。土壤厚度受到环境因子(地形湿度指数、垂直曲率、曲率、坡向、坡度、高程、覆盖度、出露基岩率和植被归一化指数)的多重影响,而表层岩溶带厚度受部分环境因子影响的同时,与土壤厚度和植被类型的相关性更高。研究结果有助于喀斯特区土壤-表层岩溶带演化机理认识,并为土壤-表层岩溶带厚度的空间预测提供科学依据。
Abstract:Objective The thickness of soilepikarst is an important index affecting the hydrological process of critical zones. The spatial heterogeneity is critical understanding the structural evolution mechanism of the key zones of the Earth and the water conservation function of the key zones of the Earth.
Methods Based on the 1.4 km2 area of the Mulian catchment in Huanjiang, Guangxi, the 1 731 soil-epikarst thickness samples were obtained through electrical resistivity tomography (ERT) with 45 sampling lines.The spatial distribution pattern of soil and epikarst thickness and its influencing factors were investigated. The results showed that the average thickness of soil and epikarst was 1.15 m and 6.44 m with strong and medium variance, respectively.
Results The results of geostatistical analysis indicated that the spherical model and exponential model could reflect the spatial structure characteristics of soil and epikarst thickness, respectively. Soil thickness showed moderate spatial autocorrelation, a long range and good spatial continuity. However, the epikarst presented strong spatial autocorrelation and spatial dependence with a short range. Soil thickness was affected by multiple environmental factors (topographic wetness index, vertical curvature, curvature, aspect, slope, elevation, coverage, outcrop ratio and NDVI), while the thickness of epikarst was more affected by soil thickness and vegetation type.
Conclusion These results are helpful for understanding the evolution of the soil-epikarst zone and provide a scientific basis for the spatial prediction of soil-epikarst thickness in karst areas.
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Key words:
- karst critical zone /
- spatial heterogeneity /
- soil-epikarst /
- vegetation type /
- dolomite small watershed
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表 1 基岩化学成分组成
Table 1. Chemical composition of bedrock
样点 灼烧减量 SiO2 Al2O3 TFe2O3 CaO MgO K2O Na2O TiO2 P2O5 MnO wB/% 东南坡 46.57 0.67 0.16 0.09 30.91 21.54 0.009 8 0.03 0.02 0.008 3 0.003 2 洼地 46.59 0.48 0.32 0.06 31.15 21.54 0.006 9 0.02 0.06 0.006 5 0.004 7 西北坡 46.49 0.36 0.26 0.04 32.19 20.45 0.005 3 0.03 0.03 0.006 6 0.002 7 表 2 土壤和表层岩溶带厚度的描述性统计
Table 2. Descriptive analysis and normal distribution test of the epikarst thickness
样本数 最小值/m 最大值/m 平均值/m 标准差 变异系数 偏度 峰度 土壤厚度 1 731 0 6.4 1.15 1.3 1.13 1.04 0.36 表层岩溶带厚度 1 731 0.5 26.8 6.44 4.37 0.68 1.36 2.33 表 3 土壤和表层岩溶带厚度的半变异函数模型及其参数
Table 3. Types and parameters of the semivariogram model for the soil-epikarst thickness
模型 块金值C0 基台值C0+C 块金值/基台值C0/(C0+C) 变程/m 决定系数R2 土壤厚度 球状模型 0.8 1.77 0.45 201 0.877 表层岩溶带厚度 指数模型 4.8 20.32 0.24 153 0.725 表 4 土壤-表层岩溶带厚度与地形-环境因子的相关系数
Table 4. Correlation coefficients between soil-epikarst thickness and terrain-environmental factors
地形湿度指数 垂向曲率 平面曲率 曲率 坡向 坡度 高程 覆盖度 出露基岩率 植被归一化指数 土壤厚度 0.149** -0.080** 0.052 -0.070** -0.087** -0.281** -0.320** -0.206** -0.377** -0.082** 表层岩溶带厚度 0.163** -0.014 0.034 -0.031 0.010 -0.151** -0.220** -0.255** -0.301** -0.275** 注:**表示在0.01水平上显著相关 表 5 土壤和表层岩溶带厚度回归方程参数
Table 5. Parameters of the regression equations of the soil-epikarst thickness
常数 地形湿度指数 垂向曲率 曲率 坡向 坡度 高程 覆盖度 出露基岩率 植被归一化指数 R2 P 土壤厚度 4.023 -0.004 0.334 -0.125 0.001 -0.029 -0.003 -0.009 -0.037 -0.219 0.215 <0.001 表层岩溶带厚度 22.33 0.118 — — — -0.006 -0.017 -0.043 -0.089 -13.63 0.177 <0.001 表 6 基于植被类型和土壤厚度划分的土表层岩溶带厚度回归方程参数
Table 6. Parameters of the regression equations of the epikarst thickness based on soil thickness and land cover
常数 地形湿度指数 坡度 高程 覆盖度 出露基岩率 植被归一化指数 土壤厚度 虚拟参数 R2 P D1 D2 D3 表层岩溶 11.932 0.063 0.001 -0.004 -0.021 -0.082 -2.503 — -0.398 -1.569 2.666 0.232 <0.001 带厚度 10.558 0.075 0.011 -0.002 -0.020 -0.063 -3.800 0.571 -0.340 -1.395 2.263 0.253 <0.001 -
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