Mechanism of Salinization of Shallow Groundwater in Western Hetao Irrigation Area
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摘要: 浅层地下水水位埋深浅、含盐量高,是导致河套灌区土壤次生盐渍化的重要原因.以河套灌区西部地区为研究区,通过对浅层地下水的水化学和氢氧同位素特征分析以及水文地球化学模拟,探讨了灌区浅层地下水的补给来源和主控水-岩作用过程,并定量估算了蒸发作用对浅层地下水含盐量的影响.研究区内浅层地下水为弱碱性咸水,pH为7.23~8.45,总溶解性固体(total dissolved solids,TDS)变化范围为371~7 599 mg/L;随着地下水咸化程度增大,水化学类型由HCO3-Na·Mg·Ca型向Cl-Na型过渡.引黄灌溉和大气降水是浅层地下水的主要补给来源,径流过程中浅层地下水受蒸发作用和植物蒸腾作用影响,地下水化学组分主要来源于蒸发盐溶解和硅酸盐风化水解,并受强烈的蒸发作用和离子交换作用影响.水文地球化学模拟和主成分分析结果显示,蒸发作用和岩盐溶解作用对区内浅层地下水咸化贡献最大,石膏和白云石等矿物的溶解、硅酸盐的水解、Na-Ca离子交换以及局部地形起伏对地下水咸化过程也有较大贡献.Abstract: High salinity and shallow level of shallow groundwater are the important causes of soil secondary salinization in Hetao irrigation area. In this paper, it takes the western part of Hetao irrigation area as the research area. The hydrochemical analysis, isotopic characteristics of hydrogen and oxygen and hydrogeochemical modeling were investigated to identify the recharge sources of shallow groundwater and the main water-rock interaction processes, and estimate quantitatively the effect of evaporation on shallow groundwater. The results show that shallow groundwater was weak alkaline salt water, the pH and total dissolved solids (total dissolved solids, TDS) are 7.23-8.45 and 371-7 599 mg/L respectively in the research area. With the accumulation of salt, the hydrochemical type of shallow groundwater changed from HCO3-Na·Mg·Ca to Cl-Na. The main recharge resources of shallow groundwater are the irrigation by using Yellow River water and precipitation. The shallow groundwater was affected by evaporation and transpiration during the runoff process. The hydrochemical compositions of shallow groundwater mainly came from the dissolution of halite and silicate weathering, and experienced intense evaporation and the cation exchange. The results of hydrogeochemical modeling and principal component analysis show that evaporation and halite dissolution contributed the most part to the salinity of shallow groundwater; Na-Ca exchange, topography variations and dissolution of gypsum, dolomite and other minerals also contributed to the salinity of groundwater.
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表 1 研究区浅层地下水主要水化学指标统计
Table 1. Statistics for the hydrochemical indexes of shallow groundwater from the study area
项目 A组 B组 C组 D组 300 mg/L < TDS < 500 mg/L(n=3) 500 mg/L < TDS < 1 000 mg/L(n=13) 1 000 mg/L < TDS < 2 000 mg/L(n=31) 2 000 mg/L < TDS(n=27) 最小值 最大值 平均值 最小值 最大值 平均值 最小值 最大值 平均值 最小值 最大值 平均值 pH 7.40 7.93 7.75 7.75 8.45 7.88 7.23 8.37 7.81 7.36 8.08 7.67 EC(mS/cm) 0.69 0.72 0.70 0.92 1.60 1.26 1.66 2.98 2.14 3.07 10.32 5.03 TDS(mg/L) 371 434 404 503 953 766 1 019 1 817 1 287 2 061 7 599 3 356 K+(mg/L) 1.74 3.15 2.21 2.21 3.96 3.16 0.91 6.14 3.49 2.47 13.74 6.05 Na+(mg/L) 44.9 99.8 71.0 89.7 227.9 140.9 176.8 521.2 325.7 316.8 2 308.1 959.7 Ca2+(mg/L) 16.3 67.1 44.9 24.3 123.6 81.2 6.9 182.5 74.8 17.5 205.5 104.6 Mg2+(mg/L) 21.8 36.3 29.6 36.9 72.4 53.0 11.1 123.1 66.5 39.5 553.4 174.2 HCO3-(mg/L) 357 455 395 269 519 411 283 1 026 627 368 1 407 875 SO42-(mg/L) 15.6 29.3 20.9 80.9 224.9 159.6 109.9 451.9 255.6 162.9 2 262.0 581.5 NO3-(mg/L) 0.60 2.43 1.52 0.53 3.77 1.84 0.84 31.08 4.36 2.22 67.46 7.48 Cl-(mg/L) 30.3 46.9 36.4 75.0 167.4 120.7 138.7 446.9 243.3 401.1 3 808.7 1 180.4 表 2 研究区浅层地下水氢氧同位素数据
Table 2. Hydrogen and oxygen isotope data of shallow groundwater in the study area
样品 δD(‰) δ18O(‰) TDS (mg/L) 高程(m) 井深(m) 样品 δD(‰) δ18O(‰) TDS (mg/L) 高程(m) 井深(m) LH-2 -50.7 -5.6 1 035.1 1030.8 13.5 H-47 -70.6 -8.5 1 293.2 1 039.9 - H-15 -78.9 -10.4 2 662.3 1 027.4 11.4 H-48 -75.6 -9.4 4 115.4 1 030.7 - H-17 -77.4 -10.5 1 426.6 1 031.9 2.6 H-53 -77.9 -9.7 6 406.1 1 030.8 - H-18 -82.4 -11.2 2 863.7 1033.1 2.5 H-54 -76.7 -9.0 7 598.6 1 026.4 2.4 H-19 -83.4 -10.6 4 083.6 1 036.1 1.7 LH-56 -78.2 -10.1 1 136.7 1 037.4 - H-20 -78.9 -10.0 7 029.4 1 025.6 2.5 LH-57 -75.3 -10.0 1 019.4 1 033.9 5.1 H-21 -72.7 -8.9 3 999.5 1 027.9 - LH-60 -67.9 -8.0 794.1 1 036.1 - H-22 -79.9 -9.8 4 601.6 1 031.2 - LH-61 -76.8 -10.1 1 278.2 1 031.0 2.2 H-25 -65.9 -7.8 3 680.5 1 028.3 8.0 H-63 -74.2 -10.0 1 261.2 1 027.8 - H-26 -71.7 -9.8 1 035.4 1 029.1 2.1 LH-65 -78.6 -10.3 2 266.5 1 031.8 - H-28 -78.0 -10.5 1 330.2 1 030.9 - LH-66 -73.8 -10.1 1 170.3 1 034.7 - LH-34 -78.5 -9.9 2 358.4 1 033.1 2.9 LH-69 -79.7 -11.0 1 179.8 1 030.1 2.2 H-40 -65.6 -7.6 1 143.3 1 034.3 1.1 LH-70 -78.9 -11.1 872.9 1 026.5 2.7 H-41 -71.8 -8.8 1 221.7 1 031.2 2.2 LH-71 -81.3 -11.0 665.5 1 034.3 3.0 H-42 -66.2 -7.5 1 553.1 1 030.4 - LH-72 -71.0 -9.7 1 089.7 1 034.1 - H-46 -68.2 -8.2 2 193.8 1 031.8 1.2 LH-73 -70.9 -9.4 2 225.8 1 030.6 - 表 3 旋转成分矩阵
Table 3. Rotated component matrix
指标 F1 F2 F3 Na+ 0.947 0.057 -0.086 K+ 0.772 0.356 -0.126 Ca2+ 0.190 0.865 -0.033 Mg2+ 0.795 0.528 -0.002 Cl- 0.918 0.129 -0.025 SO42- 0.504 0.596 -0.113 HCO3- 0.734 0.032 0.021 Si -0.010 0.732 0.032 采水井地面高程 -0.495 0.167 0.645 采水井水位 0.128 -0.128 0.912 方差贡献率(%) 47.332 15.159 12.033 累计方差贡献率(%) 47.332 62.529 74.562 表 4 逆向模拟水样数据
Table 4. Sample data used in inverse simulation
水样编号 pH Cl- SO42- K+ Na+ Ca2+ Mg2+ HCO3- 水化学类型 高程(m) 水位(m) LH-5 8.02 78 113 3.05 103 41.8 39.2 280 HCO3-Na·Mg 1 037.2 5.3 LH-35 7.83 111 150 3.24 109 81.2 36.9 382 HCO3-Na·Ca·Mg 1 035.9 4.8 H-14 8.06 196 198 2.9 400 27.9 37.3 611 HCO3·Cl-Na 1 029.9 3.7 H-38 7.78 447 234 5.4 521 63.5 66.6 911 HCO3·Cl-Na 1 030.0 3.5 注:*.除指明外,单位为mg/L. 表 5 逆向模拟结果
Table 5. The results of inverse simulation
组分 LH-5→LH-35 H-14→H-38 H2O(mol·L-1) - -4.67 NaCl(mol·L-1) 0.000 701 0 0.006 119 0 CaSO4(mol·L-1) 0.000 377 7 - CO2(g) 0.001 048 0 0.001 887 0 CaCO3(mol·L-1) 0.000 592 9 - CaMg(CO3)2(mol·L-1) - 0.000 106 2 NaX(mol·L-1) - 0.000 484 3 CaX2(mol·L-1) - -0.000 242 1 MgX2(mol·L-1) - - 浓缩倍数 - 1.084 注:*.正值表示溶解,负值表示沉淀,“-”表示未参与反应. -
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