Geochemical characteristics of water and soil environment and its environmental indicating significances since the Pleistocene in the northern flank of the Changjiang River Delta
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摘要: 江苏沿海平原是江苏省域水资源脆弱带,地下水咸化已成为较为严重的生态环境问题。为了解析长江三角洲北翼地区更新世以来地下水的补给及其盐分来源,布设一口275 m的深井HYRD1,全孔连续采集易溶盐样品、土工样品、水样。在区域采集地表水、浅层与深层地下水、海水样品。采用易溶盐指标结合土工指标(含水率、湿密度、比重)获取了HYRD1高精度孔隙水的水化学特征。采用Piper三线图、Gibbs图、离子比值法等结合δD、δ18O数据、14C测年数据解析了更新世以来地下水的补给及其盐分来源。结果表明:土体盐分主要为NaCl,盐渍土占比为25%。盐渍土主要分布在Qp3弱透水层、Qp2地层与Qp1上段地层。孔隙水水化学类型为Cl−Na型(仅Qp1下段个别点为
${{\rm{HCO}}^-_3}- $ $ {\rm{Ca}}\cdot {\rm{Na}}$ ),微咸水占比7%,咸水占比49%,盐水占比44%。微咸水主要分布在Qp1下段砂层中。潜水的δ18O、δD说明潜水来源为大气降水,且受到了较为强烈的蒸发作用。弱透水层孔隙水、承压水的δ18O、δD投点位于标准海水稀释线附近,且随着深度的增加,δ18O、δD有减小趋势,说明海水混合作用随着深度的增加而减小。Qp1弱透水层多见钙质结核,说明了Qp1地层成土后受到了强烈的蒸发作用。HYRD1 Qp1上段及上覆地层盐分主要来源于5期海侵、蒸发盐岩与硅酸盐风化溶解,Qp1下段地层盐分主要来源为地壳源。地下水化学成分受到了水岩作用、蒸发浓缩作用与人类活动等的影响。Abstract: The coastal plain of Jiangsu Province is a fragile zone of water resources in Jiangsu Province, and groundwater salinization has become a serious ecological problem. In order to analyze the groundwater recharge and its salinity sources in the north flank of the Changjiang River Delta since Pleistocene, a 275 m deep well HYRD1 was deployed and the whole hole was continuously collected with easily soluble salt samples, geotechnical samples and water samples. Surface water, shallow and deep groundwater, and seawater samples were collected in the area. The hydrochemical characteristics of Well HYRD1 high-precision porewater were obtained by using soluble salt index combined with geotechnical index (water content, wet density, specific gravity). In order to analyze the groundwater recharge and its salt source since Pleistocene, Piper trilinear diagram, Gibbs diagram and ion ratio method were used in combination with δD and δ18O data and 14C data. The results show that the salinity of Well HYRD1 soil is mainly NaCl, and the percentage of saline soil is 25%. The saline soils are mainly distributed in the Qp3 aquitard, Qp2 stratum and the upper part of Qp1 stratum. The water chemistry type of porewater is Cl-Na type (only the lower section of Qp1 is HCO$_3^- $ -Ca·Na at individual points), 7% of brackish water, 49% of saline water and 44% of haline water. The brackish water is mainly distributed in the sand layer of the lower section of Qp1. The δ18O and δD of diving indicate that the source of diving is atmospheric precipitation and is subject to a relatively strong evaporation effect. The δ18O and δD of the aquitard pore water and pressurized water are located near the standard seawater dilution line, and the trend of δ18O and δD decreases with the increase of depth, which indicates that the porewater is subjected to the mixing effect of seawater decreases with the increase of depth. Calcareous nodules are mostly seen in the Qp1 aquitard, indicating that the Qp1 aquitard was subjected to strong evaporation after soil formation. The salinity of the upper part of Well HYRD1 Qp1 and the overlying strata is mainly from the 5th stage sea erosion, evaporite and silicate weathering dissolution. The salinity of the lower part of Qp1 is mainly from the crustal source. The groundwater chemistry is influenced by water-rock action, evaporation concentration and human activities.-
Key words:
- sedimentary environment /
- saline characteristics /
- soluble salts /
- porewater /
- aquitard /
- coastal aquifers
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图 2 HYRD1岩心照片
a、b、c为Qh地层;d、c、f、g为Qp3地层;h、i、j、k、l为Qp2地层;m、n、o、p、q、r、s、t为Qp1上段地层;u、v、w、x为Qp1下段地层
Fig. 2 Core photos of Well HYRD1
a, b, and c refer to the Qh stratum; d, c, f, and g represent the Qp3 stratum; h, i, j, k, and l represent the Qp2 stratum; m, n, o, p, q, r, s, and t are the upper stratum of Qp1; u, v, w, and x represent the lower stratum of Qp1
表 1 土层按含盐量统计与分类
Tab. 1 Statistics and classification of soil layers according to salt content
层位 含盐量/% 按含盐量分类统计/% 最小值 最大值 平均值 非盐渍土 弱盐渍土 潜水(Qh,粉土、粉质黏土) 0.14 0.17 0.15 100 0 弱透水层(Qh) 0.45 0.45 0.45 0 100 微承压水(Qh) 0.16 0.25 0.21 100 0 弱透水层(Qp3) 0.20 0.59 0.38 33 67 砂层(Qp3) 0.08 0.24 0.15 100 0 弱透水层(Qp2) 0.49 0.58 0.53 0 100 砂层(Qp2) 0.09 0.46 0.26 72 28 弱透水层(Qp1上段) 0.20 0.49 0.35 10 90 砂层(Qp1上段) 0.09 0.46 0.26 8 92 弱透水层(Qp1下段) 0.06 0.15 0.11 100 0 砂层(Qp1下段) 0.04 0.07 0.05 100 0 表 2 孔隙水按照矿化度统计与分类
Tab. 2 Statistics and classification of pore water according to mineralization degree
层位 矿化度/(g·L−1) 各类型占比/% 最小值 最大值 平均值 微咸水 咸水 盐水 潜水(Qh,粉土、粉质黏土) 4.67 6.6 5.71 − 100 − 弱透水层(Qh) 19.27 19.27 19.27 − 0 100 微承压水(Qh) 7.36 11.31 8.88 − 86 14 弱透水层(Qp3) 5.91 17.46 12.2 − 50 50 I承压水(Qp3) 3.08 8.53 6.07 − 100 − 弱透水层(Qp2) 21.28 27.63 23.9 − 0 100 II承压水(Qp2) 4.91 21.27 11.37 − 45 55 弱透水层(Qp1上段) 8.16 18.14 13.23 − 15 85 III承压水(Qp1上段) 4.33 32.41 11.44 − 50 50 弱透水层(Qp1下段) 2.77 6.06 4.36 22 78 − III承压水(Qp1下段) 1.78 3.01 2.14 80 20 − 表 3 水化学类型划分统计(%)
Tab. 3 Statistical of water chemistry type classification (%)
层位 Cl−Na−B Cl−Na−C Cl·HCO3−Na−B Cl·SO4−Na−B Cl·SO4−Na−C Cl·SO4−Na·Ca−B 潜水(Qh,弱透水层) 75 − 25 − − − 弱透水层(Qh) − 100 − − − − 微承压水(Qh) 72 14 − 14 − − 弱透水层(Qp3) 50 50 − − − − I承压水(Qp3) 100 − − − − 弱透水层(Qp2) − 100 − − − − II承压水(Qp2) 41 55 4 − − − 弱透水层(Qp1上段) 21 79 − − − − III承压水(Qp1上段) 50 46 − − 4 − 弱透水层(Qp1下段) 56 − 33 − − 11 III承压水(Qp1下段) 20 − 80 − − − 表 4 孔隙水中的溶解性总固体(TDS)、Cl−、Na+含量与易溶盐指标中的含盐量、Na+、Cl−含量的相关性分析
Tab. 4 Correlation analysis of contents of total dissolved solids (TDS), Cl−, Na+ in porewater with the contents of salt, Cl−, Na+ in the soluble salt index
指标 土体 孔隙水 含盐量 Na+ Cl− TDS Na+ K+ Ca2+ Mg2+ $ {{\rm {HCO}_3^-}}$ Cl− $ {{\rm {SO}}_4^{2-}} $ 土体 含盐量 1.000 Na+ 0.988** 1.000 Cl− 0.992** 0.975** 1.000 孔隙水 TDS 0.798** 0.810** 0.773** 1.000 Na+ 0.776** 0.808** 0.747** 0.990** 1.000 K+ 0.380** 0.369** 0.357** 0.662** 0.621** 1.000 Ca2+ 0.572** 0.467** 0.615** 0.483** 0.381** 0.214* 1.000 Mg2+ 0.663** 0.574** 0.674** 0.648** 0.549** 0.570** 0.762** 1.000 $ {{\rm {HCO}_3^-}}$ −0.207* −0.174 −0.267** 0.085 0.109 0.044 −0.212* −0.299** 1.000 Cl− 0.843** 0.850** 0.833** 0.989** 0.976** 0.631** 0.542** 0.684** −0.018 1.000 $ {{\rm {SO}}_4^{2-}}$ 0.567** 0.579** 0.498** 0.853** 0.842** 0.674** 0.258** 0.558** 0.103867 0.789** 1.000 注: **表示在0.01水平(双侧)上显著相关,发生概率为99%;*表示在0.05水平(双侧)上显著相关,发生概率为95%。 表 5 孔隙水溶解性总固体(TDS)含量与土体中含盐量、Na+、Cl−含量关系拟合式
Tab. 5 Fitting equation for the relationship between porewater total dissolved solids (TDS) content and the contents of salt, Na+ and Cl− in the soil
层位 拟合关系式 x 相关系数 编号 全孔 y = 0.011 1x + 2.103 6 Na+ 0.810 (4) 全孔 y = 0.006 4x + 3.277 4 Cl− 0.773 (5) 全孔 y = 36.282x + 1.887 1 含盐量 0.796 (6) Qh y = 0.007x + 2.136 5 Cl− 0.883 (7) Qp1 y = 0.005 7x + 3.776 4 Cl− 0.778 (8) Qp1上段 y = 0.006 5x + 4.706 Cl− 0.660 (9) Qp1下段 y = 0.006 7x + 1.365 Cl− 0.937 (10) Qh y = 0.013 5x − 0.333 8 Na+ 0.858 (11) Qp1 y = 0.009 9x + 2.465 7 Na+ 0.827 (12) Qp1上段 y = 0.011 8x + 3.129 3 Na+ 0.726 (13) Qp1下段 y = 0.010 9x + 0.874 Na+ 0.930 (14) Qh y = 39.926x − 0.006 9 含盐量 0.917 (15) Qp1 y = 32.154x + 2.502 3 含盐量 0.810 (16) Qp1上段 y = 37.664x + 3.118 9 含盐量 0.693 (17) Qp1下段 y = 37.693x + 0.209 8 含盐量 0.998 (18) -
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