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河流生态系统,作为生物圈物质循环和能量流动的主要通道之一,在区域气候调节、水质净化以及维持物种生物多样性等方面起到了重要的作用[1-2]。气候变化和人类活动被认为是影响河流水文循环的两个主要因素[3-6]。在气候变化和人类活动的影响下[7],水文循环速率和路径的改变[8]导致大气和地表之间的水量和能量通量发生变化[9-10],从而影响了整个流域的水文循环[11]。因此,深入了解现代河流流域水文循环过程对恢复河流径流以及保护流域的生态环境具有重要意义。
液态水稳定同位素方法被广泛地应用于流域水循环。根据不同水体中氘(D)与氧(18O)同位素组成差异[12],被广泛的用于揭示水体的形成、运移和补给关系等过程。如郭亚文等[13]分析了黄土高原沟壑区南小河沟流域地表水和地下水的氢氧稳定同位素和水化学特征,揭示了地表水与地下水之间的相互关系;梅亮等[14]对黑河上游葫芦沟流域的各水体稳定同位素特征及各水体的水力联系进行分析探讨,运用端元混合分析模型将冻土活动层的水分来源定量化;车存伟等[15]测定了兰州市南北两山的降水、河水及土壤样品中的氢氧稳定同位素,阐明了南北两山土壤蒸发的时空变化;刘鑫等[16]分析了整个汾河流域浅层地下水的水化学和氢氧稳定同位素分布特征及其影响因素,揭示了汾河流域水循环和水质演化过程。
汾河作为黄河的第二大支流,是山西省最大的河流。近些年来,受降水减少、蒸发增大以及人类活动加剧等因素的影响,汾河流域的水资源和水环境状况已经受到严重破坏,出现了河道断流、地下水水位下降、泉水干涸、水质污染等现象[4,17-18],流域经济社会的可持续发展和生态环境建设已受到严重制约。汾河上游流域作为汾河流域重要的生态屏障,同时是山西省会太原的水源涵养地和供水区,其水资源质量对汾河上游甚至整个流域的人民生产和生活有着重要影响。为了让这条山西的母亲河“水量丰起来”,开展汾河上游的水源解析是十分必要的。因此,本研究以汾河上游为研究对象,利用稳定同位素方法,阐明不同水源的同位素特征和补给关系,为汾河上游的河流生态保护提供科学依据。
汾河源头水源稳定同位素特征及水源解析
Stable isotope characteristics of the headstream region of Fenhe River and water resource analysis
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摘要: 针对汾河源头水的来源不清楚的问题,以宁武地区汾河源头流域为研究区,通过系统采集区域内河水、湖水以及浅层地下水样品,运用水体化学离子分析和氢氧同位素技术,确定区内各水体的水化学特征、氢氧同位素特征及其水力联系,运用端元混合模型(EMMA)量化河水的水分来源。研究表明,河水与浅层地下水的电导率沿程变化从上游至下游呈上升趋势,且两者对比变化不明显。汾河源头区域浅层地下水、河水的优势阴阳离子为
${{\rm{HCO}}_3^{-} }$ 和Ca2+,湖水的优势阴阳离子为Na+和${{\rm{HCO}}_3^{-} }$ ,浅层地下水、河水的水化学类型以Ca·Mg-HCO3为主,湖水的水化学类型主要为Na- HCO3,河水与浅层地下水的离子来源主要是岩石风化作用。以太原地区大气降水氢氧同位素值建立汾河源头区域大气降水(LMWL)方程,当地河水、湖水、地下水蒸发线方程为δD=4.9δ18O−21.4,蒸发线方程的斜率与截距均比全球大气降水和当地大气降水方程小,表明河水在运移路径中经历了一定的蒸发作用。河水的δ18O、δD值从下游至上游区域呈现下降趋势,并有一定的海拔效应。河水、湖水、地下水的同位素值基本落在当地大气降水线两侧,证明大气降水为汾河源头区域各类水体的主要来源,并且河水、地下水离子含量变化相似,稳定同位素值相近,结合电导率沿程变化,证明地下水和河水存在紧密的水力联系。以d excess作为示踪剂对河水进行二元端元混合模型计算,大气降水占比为70.6%,为河水的主要水分来源。Abstract: In this paper, in response to the problem that the source of the water of the headstream region in Fenhe River is unclear, the headstream region of Fenhe River which is represented by Ningwu county, Shanxi Province was used as the study area. Through field investigation, the water samples including rivers, lake water and shallow groundwater were detected for water chemical ion analysis and environmental isotopes to reveal the water chemistry characteristics and stable isotopes characteristics of different water bodies and analysis the hydraulic connection between water bodies. Besides, the quantitative analysis of the water source in rivers was carried out by End-Member Mixing Analysis (EMMA) model. The study results show that electrical connectivity values of rivers and shallow groundwater increased from the upstream source region to the downstream region. Meanwhile, electrical connectivity between rivers and groundwater is in little differences. The dominant anions and cations of shallow groundwater and river water in the source area of Fenhe River are${\rm{HCO}}_3^{-} $ and Ca2+, nevertheless, for the lake water, the dominant anions and cations are Na+ and${\rm{HCO}}_3^{-} $ . The hydrochemical types of shallow groundwater and river water are mainly Ca·Mg-HCO3, the main water chemical type of lake water is Na- HCO3. The ion source of river water and shallow groundwater is mainly rock weathering. Based on the stable isotope values of precipitation in Taiyuan City, the equation of Local Meteoric Water Line (LMWL) in Fenhe River’s headstream region is built, the river, groundwater, lake water Local Evaporation Line Equation (LEL) is δD=4.9δ18O-21.4, the slope and intercept are smaller than those of the Global Meteoric Line(GMWL) and LMWL, which demonstrates that the river has experienced strong evaporation within flow path and the δ18O, δD values of rivers show a downward trend from downstream to upstream with an altitude effect to some extent. The stable isotope values of river, lake water and groundwater are distributed in both sides of LMWL, which indicates that precipitation is the main source of different water bodies in Fenhe River’s headstream region. Meanwhile, river water and groundwater ion content changes similarly, stable isotope values between both water bodies are similar, combined with changes in electrical conductivity along the way, these phenomenon indicate that close hydraulic connection between river water and groundwater. In order to analysis the contribution of precipitation and groundwater to Fenhe River, Binary EMMA was applied to calculate by the values of d excess as the tracers, respectively. The model results show that the river water mainly comes from precipitation, with a contribution rate of 70.6% . -
表 1 汾河源头区样品稳定同位素值和电导率值
Table 1. Stable isotope values and electrical conductivity values of samples from the source area of Fenhe River
样品类型
Sample types样品编号
Sample IDδ18O/‰ δD/‰ d excess/‰ 海拔高/m
AltitudeEC/(μS·cm−1) 地下水 J1 −9.7 −71 7.1 1526.04 72.2 J2 −10.0 −73 7.1 1603.54 476 J3 −9.9 −72 7.2 — 910 J4 −10.2 −73 8.6 1765.57 515 JC −10.6 −73 11.5 1484.62 205 BD1 −11.1 −76 13.6 1693.14 278 BD2 −11.2 −75 14.2 1869.77 399 F1 −11.1 −76 13.1 1574.42 284 河水 LY1 −9.8 −71 7.8 823.29 458 LY2 −9.8 −70 8.0 923.33 255 LY3 −10.2 −73 9.2 1264.15 207 LY4 −10.4 −73 10.3 1264.98 377 LY5 −10.3 −73 9.6 1525.96 207 H6 −9.9 −71 7.7 1516.13 1140 H7 −10.0 −70 9.3 1515.83 714 H9 −10.7 −77 8.8 1714.11 1600 H10 −11.0 −79 9.1 1770.19 1426 NQG1 −8.4 −64 3.2 1751.14 406 河水 NQG2 −10.0 −71 9.2 1757.41 235 LPG −10.7 −73 12.1 1751.18 179.5 MDG −10.3 −71 10.9 1629.26 346 DM −11.0 −75 13.6 1628.27 242 ML1 −10.7 −73 12.7 1963.70 229 ML2 −10.9 −74 13.5 1677.00 180.2 LV1 −9.6 −71 6.3 — — LV2 −10.2 −71 10.7 — — LV3 −9.2 −66 7.9 — — 湖水 TC −0.7 −25 −20.1 1753.51 352 PPH 0.1 −21 −22.1 1760.31 445 GH1 −0.1 −21 −20.5 1833.95 849 GH2 −0.2 −21 −19.3 1834.60 690 注:—代表数据未获取.
Note: —represents data not obtained表 2 汾河源头区不同水体主要离子浓度分析(mg·L−1)
Table 2. Statistics of major components of water samples in the source area of Fenhe River(mg·L−1)
水体类型Water types 项目Items Ca2+ Mg2+ Na+ K+ ${\rm{HCO}}_3^{-} $ ${\rm{CO}}_3^{2-} $ ${\rm{SO}}_4^{2-} $ C1− TDS 地下水 (n=6) 最大值 236.10 40.27 24.59 5.74 700.28 68.44 99.40 11.99 551 最小值 10.53 16.00 5.40 2.38 16.96 3.84 0.00 1.56 36 平均值 91.58 25.44 15.15 3.25 303.70 26.72 23.40 4.91 211 标准差 69.19 7.26 7.05 1.07 228.37 22.46 36.33 3.61 201 河 水(n=17) 最大值 384.52 46.54 77.39 10.84 1065.06 215.31 200.23 37.81 792 最小值 13.24 10.06 4.99 1.86 1.04 0.48 0.00 0.00 90 平均值 76.48 23.12 21.06 5.00 253.43 47.56 33.54 6.96 244 标准差 109.41 10.09 19.28 2.88 331.74 60.74 54.07 8.44 212 湖 水(n=4) 最大值 23.18 19.34 201.16 36.09 740.54 248.30 56.07 33.37 424 最小值 7.97 6.93 29.57 6.60 85.83 14.79 0.00 8.21 176 平均值 13.33 12.33 110.65 20.04 376.19 97.99 19.51 21.40 292 标准差 5.88 5.27 77.17 13.51 282.61 92.32 22.93 11.38 98 表 3 汾河源头区不同水体的参数值
Table 3. Parameter values of different water bodies in the source area of Fenhe River
水体类型
Water type样品个数
Nunber of samplesδ18O d excess 平均值Mean 标准差Standard deviation 平均值Mean 标准差Standard deviation 浅层地下水 7 −10.5 0.59 10.3 2.98 降水 8 −10.0 2.50 10.2 4.42 河水 26 −10.2 0.75 10.2 2.99 表 4 太原地区大气降水同位素数据统计
Table 4. Statistics of isotope data of atmospheric precipitation in Taiyuan
日期Date δ18O δD d excess 3-15 −13.8 −94 16.4 6-15 −7.1 −44 13.1 7-15 −7.1 −52 4.4 10-15 −13.2 −89 16.2 6-15 −11.3 −86 5.1 7-15 −11.1 −81 7.2 8-15 −8.4 −56 10.9 9-15 −8.3 −59 8.0 平均值 −10.0 −70 10.2 -
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