| Water resource is valuable for living and development of humans, however, due to the development of society economy especially the acceleration of industrialization and urbanization, water shortage has been a worldly crisis. Hebei plain, north of China, is one of representative water-deficient areas and also one of adequate utilization and development of groundwater in our country. A series of geo-environment problems including drop of groundwater lever, quantity shrinkage of groundwater, worsening of water quality, land subsidence and so on happen with long term exploitation of groundwater. Hence, recognizing the dynamic change of groundwater under human activities and discipline of solute transport in groundwater plays a significant role in scientific management groundwater resource.Chlorine isotope has been widely used in study of groundwater movement and solute transport. Chlorine as a main component in groundwater is hard to form soluble minerals which is also hardly adsorbed by the clay mineral and accumulated by creatures. Because of this features, chlorine can transport free in groundwater. Chlorine isotope has simple fractionation mechanism comparing with hydrogen and oxygen isotope. So it can be used better to research discipline of solute transport in groundwater which could indirectly reflect the movement and evolvement of groundwater.Based on the comprehensive analysis of hydrogeology condition of Hebei plain, representative profile (Baoding-Changzhou-Huanghua) is selected to study chlorine isotope in groundwater. Samples were taken in 2009.9 and 2009.10. Through the relationship analysis among chlorine isotope, hydrochemistry and hydrogen-oxygen isotope of samples, we the distribution characteristics of chlorine isotope and source of chlorine in groundwater under human activities are known. Then indication value of chlorine isotope is discussed.Through the analysis of chlorine isotope from 36 groundwater samples in different aquifers, there is obvious fractionation ranging from 1.42‰to 1.04‰. The chlorine isotope value in four aquifers is different individually. There are only five samples in superficial aquifer (Q4), but the chlorine isotope value(CIV) is not only positive but also negative. The interval is 0.41‰-0.19‰. The CIV of the three confined water(Q2) range from-0.88‰to+1.04‰. The CIV is all positive in the eastern part and is the same as seawater (about 0.00‰) in the middle part around Ziya River and is negative in the middle of Cangzhou city. This show that the CIV become to be negative gradually following the direction of groundwater flow. In the four confined aquifer (Q1), the CIV range from -1.42‰to 0.00‰. In mountain front and central plain, the CIV is under measuring accuracy and it shows little chlorine isotope fractionation. However, the CIV is all negative in coastal plain which is lower than -0.20‰with the lowest value -1.42‰. Be worth mentioning, the CIV has positive correlation with chlorine concentration. The correlation coefficient is more than 0.99. There are only three samples in the five confined aquifer. The CIV is all negative ranging from -0.35‰to 0.21‰.Combining with geological condition, hydrochemistry and hydrogen-oxygen isotope information, the indication value of chlorine isotope in groundwater is discussed in this area:①indicating the recharge source of groundwater. Three possible recharge source of the groundwater is proposed:rainfall,leakage recharge and clay draining. The hydrogen-oxygen isotope value reveals the superficial groundwater originates from rainfall. According to the CIV of rainfall measured before, the CIV of rainfall should be positive in this place. When groundwater is recharged only by rainfall, the CIV should be the same (positive or negative). That is to say, the CIV of the passing water is more positive than before. We can use the clay draining to explain the CIV of Q2 in the middle of Cangzhou ranging from -0.2‰to-0.88‰. The chlorine iron will also enter into the aquifer when the clay aquitard drains. Because 35Cl is more active than 37Cl,35Cl will enter into the aquifer preferentially which could lead the CIV to become smaller.②indicating the source of chlorine. The TDS increases with the direction of groundwater flow in the first phreatic aquifer (Q4) besides Huanghua region with exceptional higher TDS where chlorine content increases from 129mg/L to 300mg/L abruptly. Through the analysis of chlorine isotope and hydrochemistry, there are two possible sources of chlorine in this region: one is adjoining rock leaching, the other is deep groundwater (deep groundwater flows upward through the fault distributing two sides of Huanghua depression to bring chlorine).GasBenchⅡ-IRMS online measurement for inorganic chlorine isotope in groundwater is established. Based on this measurement, we systematically research the composition and distribution discipline of chlorine isotope of groundwater in Hebei plain and discuss the formation mechanism and indirection value of chlorine isotope in this thesis. |
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