| Henan possesses the largest provincial population in China, and the economy is strong, it is also one of the largest water usage provinces in north China. As part of the Huang– Huai - Hai plain, its plains have important strategic position for the development of the central and western economies. Groundwater is an important water source for industrial and agricultural production and domestic water in Henan plain and plays an important role in the economic and social development of Henan plain. However, due to the unreasonable exploitation of groundwater in Henan plain, a series of environmental geological problems such as the continuous decline of the groundwater level, groundwater pollution, land subsidence and ground fissure have emerged. Having realized the sustainable development of the economy and sociality of Henan plain even the whole province, the quaternary groundwater (the main sources of water extraction) system in Henan plain was studied for the rational exploitation and utilization of groundwater in this paper, with the groundwater system theory as a guide and combining with the actual situation of the study area. Based on the division of systems, the cycle pattern of the quaternary groundwater in Henan plain was revealed, on the basis of the water chemistry and isotope data, considering the hydrogeological conditions of the study area. Then the renewability of the quaternary groundwater in Henan plain was evaluated through establishing the renewability evaluation index system.The main achievements acquired in this study are as follows:1. The classification of groundwater systemAccording to the distribution characteristic of the groundwater flow and the surface watershed which it belongs to, and whether the groundwater having a unified flow field, the quaternary groundwater system of Henan plain is classified into three first-class systems, which are northern plain groundwater system (Yellow and Haihe River Basin groundwater system) (I), central plain groundwater system (Shahe and Ruhe River basin groundwater system) (II), and southern plain groundwater system (the main stream of Huaihe River groundwater system) (III).According to the difference of hydrodynamic characteristics and water cycle pattern in vertical direction of groundwater in the system, each first-class system is further divided into shallow and deep subsystems, which are shallow groundwater sub-system of northern plain (I1), deep groundwater sub-system of northern plain (I2), shallow groundwater sub-system of central plain (II1), deep groundwater sub-system of central plain (II2), shallow groundwater sub-system of southern plain (III1) and deep groundwater sub-system of southern plain (III2).2. Groundwater cycle pattern(1) The comprehensive utilization of multi-phase isotope data Because of the limitation of the project funds, the sampling of isotopes focused on Zhumadian– Runan– Pingyu area in the central south of Henan plain and two sides of the Huaihe River in the south of Henan plain, thus the isotope samples are less and centralized distribution. Therefore, for analyzing the groundwater cycle characteristics of the entire Henan plain, it is essential to collect and make full use of previous isotope data sampled in Henan plain. However, the time span of isotope data in this research is quite wide, which is 6 to 7 years, and the isotopic content in water may change with time and environment, therefore, how to use the existing isotope data has become the key problem that must be firstly solved in this research.The approaches in this study are as follows:①PrecipitationOn the basis of analyzing the test results of multi-phaseδ18O andδD isotope in precipitation, the annual average was chose as theδ18O andδD value in precipitation.Considering the latitude effect of 3H isotope of precipitation and the actual situation of Henan plain (the latitude across 4°12′in south-north direction), Zhengzhou station and Wuhan station which is nearest to the south of Henan plain were chosen as typical stations. The historic series (from 1956 to 2007) of 3H concentration in precipitation at typical stations have been recovered with many methods. Taking the 3H concentration in precipitation to represent the 3H concentration in precipitation on two sides of Yellow River, and taking the average value of the 3H concentration in precipitation at Zhengzhou station and Wuhan station to represent the 3H concentration in precipitation on two sides of Huaihe River, the research was carried out. And the results show that the 3H concentration in precipitation is 11.18TU in Yellow River and the area along it in 2007, and it is 10.16TU in Huaihe River and the area along it②Surface waterAfter analyzing the test results of multi-phaseδ18O andδD isotope in surface water, the original test data without any treatment were chose as theδ18O andδD value in surface water.The correlativity between 3H value in surface water and time was studied through correlation analysis according to the collected test results of multi-phase 3H isotope, and 3H concentrations in surface water in the research area in 2007 were estimated.③GroundwaterHaving analyzed the test results of multi-phaseδ18O andδD isotope in groundwater, the original test data without any treatment were chose as theδ18O andδD value in groundwater.Based on considering the moving situation of 3H in groundwater and the optimal model used in the groundwater age calculation, the 3H concentrations in groundwater in the research area were decayed to 2007 according to exponential law, and then used in the research of water cycle pattern.δ13C and 14C were used in calculating the age of groundwater, taking the original test results.(2) The relationship between precipitation, surface water and groundwaterBased on analyzing the distribution of water chemistry and isotope of precipitation, surface water and groundwater in Henan plain, the relationship between precipitation, surface water and groundwater in the research area has been found out.The Yellow River in northern plain is mainly recharged by the secondary water from the middle and upper reaches of Yellow River and the precipitation (the Weihe River is mainly recharged by precipitation and groundwater), both the main and the branch of Huaihe River in central south of Henan plain is recharge by groundwater besides precipitation, so theδ18O andδD values in Huaihe River have little difference in wet and dry seasons, and their distribution characteristics are consistent with groundwater,The shallow groundwater in Henan plain is originated from precipitation, and has been influenced by evaporation. In northern plain, the lateral recharge of Yellow River is also the main recharge source of shallow groundwater along Yellow River. So in Yellow River and the area along, theδ18O value in groundwater concentrates on Yellow River and distributes as"∨"shape, and the 3H value concentrates on Yellow River and distributes as"∧"shape. The range of lateral infiltration zone in different place along Yellow River is determined primarily according to the distribution characteristics ofδ18O value in shallow groundwater at sections. The lateral infiltration zone in the north and south bank of Yellow River at the section of Yuanyang - Zhengzhou is 6 km and 10 14 km separately, at the section of Xinxiang– Zhongmou is 17 km and 25 km, at the section of Fengqiu– Kaifeng is 15 km and 26 km, and the lateral infiltration zone in the north bank of Yellow River at the section of Puyang section is 5km.The deep groundwater in Henan plain also originated from precipitation, and is less influenced by evaporation. In areas with large exploitation, the leakage of shallow groundwater has been its main recharge source.(3) The cycle pattern of the quaternary groundwater in Henan plainThe cycle characteristics of Quaternary groundwater in Henan plain were studied by isotope as the main analysis method, combined with hydrogeological conditions and the water chemistry distribution regularity. The results show that the groundwater cycle pattern in Henan plain can be concluded to three kinds.①The water cycle pattern that mainly recharged by precipitation and surface water, good runoff conditions, strong groundwater exploitationThis water cycle pattern exists in northern plain groundwater system (I). The groundwater is mainly recharged by precipitation and the infiltration of Yellow River, the condition of groundwater runoff is good, the average age of shallow groundwater is 35.29a, and the deep groundwater is 9726.52a. There is a regional concave valley at Mengzhou - Wenxian - Wuzhi - Xinxiang - Huaxian - Puyang - Qingfeng - Nanle area which has large groundwater exploitation, groundwater converges here and flows out of Henan province along northeast direction.②The water cycle pattern that recharged by precipitation, bad runoff conditions, strong groundwater exploitation, mainly vertical water cycleThe water cycle pattern exists in central plain groundwater system (II). The groundwater is mainly recharged by precipitation. The groundwater is closely related to precipitation, and the water cycle is mostly vertical alternation, the horizontal runoff condition is poor, the average age of shallow groundwater is 39.93a, and the deep groundwater is 8096.53a. A drainage area has formed at Wohe and Yinghe River. There is a regional concave valley at the northern boundary of Zhengzhou - Kaifeng - Shangqiu area due to excessive groundwater exploitation.③The water cycle pattern that recharged by precipitation, good runoff conditions, mainly discharged to riverThe water cycle pattern exists in southern plain groundwater system (II). The groundwater is mainly recharged by precipitation. It flows to the plain areas from the front of Tongbai Mountain and Dabie Mountain, and Queshan - Zhengyang -Xincai area (watershed). The hydraulic slope is large, and the runoff condition is good, the Huaihe River is the regional groundwater discharge channel. The average age of shallow groundwater is 37.71a, and the deep groundwater is 4362.37a.3. The renewability of groundwaterThe renewability of groundwater represents the ability of renewing and restoration of groundwater during water cycle. The renewability of the quaternary groundwater in Henan plain was evaluated using single index and the establishment of index system.The renewability of the quaternary groundwater in Henan plain was evaluated using the single-index method separately with three indexes such as groundwater recharge rate, groundwater age and exploitable groundwater resources module. The evaluation results are different from each other, based on which, the renewability evaluation index system is established according to the principle of"target– principle– index". The results show that the renewability of shallow groundwater in Henan plain is strong, and has the trend that gradually stronger from south to north, the renewability of deep groundwater in deep groundwater sub-system of southern plain is medium, in northern and central plain is weak.Compared to the single index, the index system is more comprehensive at considering the influencing factors, thus its evaluation results are more reliable.4. Some suggestions on exploitation scheme of Quaternary groundwater in Henan plainAccording to the results of the evaluation of the groundwater renewability, considering the water quality and the development & utilization of groundwater in the study area, several recommendations are presented to the exploitation of the quaternary groundwater in Henan plain as follows(1) Pay attention to the development and management of groundwater, enhance the dynamic monitoring on the groundwater level and groundwater quality as well.(2) Exploit the groundwater in a rational way,, in order to maintain the renewability of groundwater.(3) The exploitation of groundwater in the southern plain, especially along the Yellow River can be expanded properly, while in the central plain it should be controlled or reduced to protect the groundwater in deep subsystem. Besides, the groundwater in deep subsystems shouldn't be exploited further in the whole plain. Consequently, the exploitation distribution should be adjusted appropriately in order to improve the situation of excessive extraction.(4) Strengthen the control and treatment of the shallow groundwater pollution, to exploit further shallow groundwater with the protection of the deep groundwater quality.
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