Groundwater Recharge History and Its Responses to Climatic Change
|Keywords||Groundwater recharge Chloride ion Climate Change Desert - loess transition zone|
Earth system atmosphere - hydrosphere - lithosphere - Biosphere interaction, which is the most critical, the most active, the most important link between terrestrial water system, the water cycle. The water circle by climate and environmental change as well as the impact of human activities, and determine the formation of water resources and soil and water environment evolution. Precipitation in China uneven distribution of water shortages, floods and soil erosion and water-related ecological - environmental issues are very prominent. Context of global change, the characteristics of the terrestrial water cycle changes, trends, and soil and water resources security is a major demand of the National Water Research in the Earth system water frontier disciplines and applied basic. Vadose zone in the atmosphere, lithosphere, hydrosphere, biosphere interface is an important part of the precipitation into groundwater and understand the circle between matter and energy into key parts of the law. Global climate change is not only caused changes in groundwater levels and excretion, and caused a redistribution of space on the groundwater resources. These changes not only involved in the exchange of water with the aquifer, and the most rapidly, most strongly affect the vadose zone water. Thus vadose zone is the entry point for the history and characteristics of the study area, groundwater recharge, and study the the groundwater evolution of the global changes in the relationship between the important ties. Desert in northern Shaanxi - loess transition zone is located in the Tail region of the East Asian summer monsoon front, is typical of the arid and semi-arid environment. Rainfall in the region between 200-400 mm, evaporation is 2000mm above the water shortage, the ecological environment is fragile, sensitive response to climate change. The area is rich in oil, natural gas and mineral resources, it has become China's new energy and chemical industry base. However, due to the severe shortage of surface water in the region, the potential for groundwater development, energy development and water use will largely depend on the limited groundwater resources, sustainable development and utilization of groundwater resources is related to the protection of the ecological environment, local economic construction The major problems. Storage and its dynamics Therefore, the study of the history of regional groundwater recharge for understanding the background of the historical evolution of regional groundwater resources and utilize the potential of the master of groundwater resources in the region, and the region is rational development, utilization and management of groundwater resources has important theoretical and practical significance. On the other hand, the district is located in the desert - loess boundary belt, the thickness of the vadose zone quite different, thick shallow 1 m to over 20 m, relatively thick vadose zone records longer time scale precipitation recharge groundwater historical. Therefore, the region is also home to study one of the best area of ??climate change and groundwater recharge in the history of their relationship in this article through the desert in northern Shaanxi - loess transition zone four locations to carry out the drilling and sampling, testing different samples of the depth of chloride ion concentration, moisture content other indicators, the extraction of groundwater in the vadose zone hydrology - Climate saved information to restore the historical process of groundwater recharge, and analyze the possible mechanism to identify the impact of climate change on groundwater recharge. Chemical elements and water to the vadose zone proxies reconstruction of the history of the regional environmental change, and discussed with the regional and global changes. This article focuses mainly on four aspects: (1) through the transition zone of northern Shaanxi desert - loess four groundwater vadose zone water chemistry profile analysis using traditional, and generalized chlorine mass balance approach to extract the vadose zone chlorine profile The groundwater recharge records reflect the information; (2) combined with the change in characteristics of the study area is measured climatic elements of groundwater recharge response to climate change; (3) the use of the vadose zone chlorine profile rebuilt over the past century in the study area climate change history; (4) to discuss the direction and focus of regional development and utilization of water resources in the context of climate change. Through research, to obtain the understanding of the following aspects: First, to confirm the reliability of the chloride ion tracer groundwater recharge, groundwater recharge historical reconstruction of the study area the vadose with chlorine profile record. The test results showed that the four vadose zone profiles derived from atmospheric deposition average Cl-concentration is very close to a large difference in the concentration of SO42-, illustrate the impact of atmospheric deposition Cl-concentration is mainly affected by the distance of space for large-scale land and sea, and SO42- human activities affect the concentration is limited by the small scale of the space, there is a lot of space variability, proved the study area is not suitable for using Cl-SO42-extraction of groundwater recharge information. Based the generalized chlorine mass balance method (GCMB method) rebuilt the Shenmu ditch palm (GZ) Yokoyama under Shagou (XSG), Yulin Ge seeking river (GQH) three chlorine profile record 11 years, 21 years and 37 years of groundwater recharge process. GZ profile is relatively stable period of record 1990-1991 1992-1996 1997-2000 three groundwater recharge; the XSG profile records 1981-1991, 1992-2005 1995 1996-2002 2001 groundwater recharge is relatively stable The period; GQH profile recorded 1967-1970 ,1971-1975 1976 - 1995 1996-2003, a relatively stable period of four groundwater recharge. The longest stable period of the three sections GZ, XSG, GQH record average precipitation infiltration coefficient were 14.5%, 12.6% and 12.4%, average groundwater recharge intensity 53.4mm, 47.2mm and 47.1mm respectively. Second, confirm the role of the master of the annual precipitation of regional groundwater recharge, at the same time reveal other than annual precipitation, temperature and vegetation, and other factors that the chloride ion concentration changes effective record of regional climate and environmental impact on groundwater recharge, changes can be used as a reliable alternative indicators of climate and environmental change. The the GZ, XSG, GQH three sections chlorine ion concentration changes recorded groundwater recharge history and the region in the instrumental record of meteorological elements (temperature and precipitation) The comparison showed that the annual precipitation is dominant factors that control groundwater recharge intensity. The three sandy the chlorine profile changes very similar to which they consistently recorded by regional climate changes caused by the change of groundwater recharge. Especially the three chlorine profiles recorded decreased significantly since the late 1990s, a result of reduced precipitation and groundwater recharge. However, the change of the composition of precipitation, temperature, and climate change led to the vegetation, the response to annual precipitation is not strictly linear groundwater recharge. Precipitation composition, temperature and vegetation changes in groundwater recharge can enhance or weaken the response to precipitation, groundwater recharge and annual precipitation changes and even lead to an opposite trend during certain hours. Third, the reconstruction process of climate change for the past nearly a hundred years of the study area. CMB extraction of Yokoyama (HS) sandy loess vadose zone chloride profiles recorded over the past century the groundwater recharge process. Chlorine concentration as proxy indicators reflect changes in groundwater recharge compared with precipitation in the instrumental record show that groundwater recharge intensity changes on the trend with the average annual precipitation in a good corresponding relationship, further confirmation that the annual precipitation control of groundwater recharge The strength of the dominant factors. On this basis, according to the status of the annual precipitation of the period of instrumental records in the reconstruction of nearly a century of changes in HS chlorine profile. The results show that, the last century, in the absence of instrumental records from the late 1930s to the mid-1940s, as the rainfall in the dry period; the mid-1940s to the mid-1950s, this area of ??precipitation above normal, the climate for the past more than 70 years Best wet period. Moreover, of Yokoyama profile reconstruction of chloride ion precipitation records, and eastern China (100 ° east longitude east) in 1921-2002 precipitation anomalies change better comparison shows that the vadose zone chloride profile record of Groundwater Recharge regional climate change in the context of global change is indicative and may provide a new approach for this environmentally sensitive zone short scale paleoclimate research. To discuss the direction and focus of regional development and utilization of water resources in the context of climate change. Sensitive to climate change in northern Shaanxi desert - loess transition zone, the groundwater environment is affected not only by the control of the area of ??natural and man-made factors, also driven by global change background. Climate change impact on groundwater in the different time scales, from seasonal to year, decade, century to the thousand years scale. Shallow aquifer system on seasonal to decadal time scales are more sensitive to climate change. In order to safeguard the sustainable development and utilization of groundwater resources, the development and utilization of groundwater in the study area should be targeted mainly shallow groundwater. Therefore, the importance to carry out the impact of climate change in the context of global change on regional shallow groundwater and targeted to develop sustainable development strategies for the rational use and protection of shallow groundwater resources in the region, the water demand for local economic development to provide protection is important. The research carried out in this article, is a combination of typical arid and semiarid zones groundwater circulation and climate change research a try, is also a new field of scientific research of the global Earth system, as a new exploration needed from a different angle and direction to carry out more in-depth research.