Compilation of Groundwater Quality Map and study of hydrogeochemical characteristics of groundwater in Asia

YI Qing, GE Li-qiang, CHENG Yan-pei, DONG Hua, LIU Kun, ZHANG Jian-kang, YUE Chen

Institute of Hydrogeology and Environmental Geology, Shijiazhuang 050061, China

Abstract: The groundwater quality map is among a series of Asian groundwater environment maps, which has been compiled and is about to be published. The article introduces the central theme and main content of the map, evaluates the method applied for groundwater quality gradation, and discusses hydrogeochemical characteristics of Asian groundwater. The distribution of water quality is investigated through the data collection of selected elements;hydrogeochemical characteristics are demonstrated via the analysis of elements’ allocation in horizontal and vertical zones; whilst the groundwater quality is evaluated by the Analytic Hierarchy Process (AHP).

Keywords: Groundwater quality; Asia; AHP; Hydrogeochemistry

Introduction

In general, maps of groundwater quality compiled outside of China, mainly focus on the application of total dissolved solids as the index for evaluation. As an illustration, within over fifty hydrogeological maps, compiled by the Federal Institute for Geosciences and Natural Research in 2013, the map of environmental geochemical groundwater quality (BGR, 2013) especially has adapted such perspective: the same as the maps of groundwater salinity distribution, focused on countries, such as: USSR, Mongolia, India, Iran,Thailand and so forth (The Soviet Union Geology Ministry, 1982a, b, c; Mongolia Institute of Geology and Mineral Resources, 2003; Geological Survey of India, 2002; Iran Bureau of Mineral Resources and Water Resources Survey, 1989; The Ministry of Industry of Thailand Mineral Resources Bureau, 1983). What is more, the Genesis Map of Saline Groundwater of the World(UNESCO, 2006; IGRAC, 2009), compiled by UNESCO in 2006, which outlines the worldwide distribution of groundwater salt in different grade,receives criticisms on its validity and further scrutiny is required.

As the pioneer of evaluating groundwater quality in China on a large scale, The Map of Underground Water Quality Evaluation and Pollution Protection Grading of China (FENG Xiao-ming et al. 1999), which is based on 90’s chemical analysis data of groundwater, presents central features and basic situation of its quality,and discusses the dual influences of possible natural and artificial factors. Moreover, The Map of Groundwater Environment in China (ZHANG Zong-hu and SUN Ji-chao, 2006), drawn by the team led by SUN Ji-chao in 2006, who took account of a fresh group of data of groundwater resources, presents the spatial distribution of the groundwater quality in China in a systematical fashion, and shows the condition and the development of groundwater environment. Even though the research carries on a regional scale,similar investigations covering different continents are limited (LIAO Zi-sheng et al. 2003; WANG Shan et al. 2004; WEN Dong-guang et al. 2012).

All in all, the investigation of groundwater quality on continental scale is still at its initial stage. Nevertheless, researches on groundwater and hydrogeochemistry of Asian regions are able to advance the development and utilization of natural resources, with not only a detailed practicable plan for Asian environmental protection, but also a refined data base for future hydrological geology researches on an international level.

1 Idea, content and method of the map

1.1 Mapping idea

The data base of Asian groundwater salinity and distribution of selected elements has been contributed and refined by the cooperation between major Asian research institutions and well-known international organizations, such as United Nations Educational, Scientific, and Cultural Organization (UNESCO), Commission for the Geological Map of the World (CGMW),and International Association of Hydrogeologists(IAH). Furthermore, several maps of single element have been published to cover the groundwater salt content, with the condition of its superficial zone, and the distribution of fluorine(F), arsenic (As), iron (Fe), manganese (Mn), and radon (Rn). Moreover, The Ground Quality Map of Asia is compiled through the method of AHP, and Fig. 1 shows the legend of this map.

1.2 Content and expression form

The Ground Quality Map of Asia is made up with two components:

A master map, which indicates the distribution of groundwater quality and selected elements (F,As, Fe, Mn and Rn);

Two embed maps, which include a hydrogeological map, introducing different groundwater types and their storage capacity, and a groundwater environment background map, presenting the zonages of environmental background of groundwater, and of hydrologic geochemistry.

In the form of content, it opens with an assessment on the quality and security of groundwater in a synthetical perspective, then moves to the division of zonage based on hydrochemical types and regional hydrogeochemical effects, and finally concludes with a discussion of the possible influences and treatments towards original chemical compositions,threats towards environment and living organisms.

Fig. 1 Legend of groundwater quality map of Asia

In the form of presentation, the application of solid colors, planar symbols and dot notation keeps a consistent relationship between visual senses and graphic expression. The illustration of groundwater quality grades includes three parts, where the first one separates different levels of groundwater quality in the form of solid colors; the second one indicates the distribution and geochemical characteristics of certain chemical elements, as well as causes of various levels of groundwater quality, in the form of planar symbols in different colors and shapes; and the third one differentiates water quality in different hydrogeochemical zonages and types, and discusses causes and circumstances of the presence of certain chemical elements, in the form of colorful linear symbols. In addition, two extra embed maps are able to clarify any ambiguity raised by the master map, indicate the interactional water-rocky zonages, and analyze the distribution of groundwater in spatial and temporal dimensions.

1.3 Method to grade groundwater qualities

Grade estimation:

To use Total Dissolved Solids (TDS) as the basis for classification;

To downgrade TDS in reference to the distribution of certain chemical elements;

To classify the quality according to the method of AHP and overlay analysis;

The Assigned weight value of certain chemical elements: To assign the weight value in relation to the effects of damage on mortal conditions;

Total value of certain chemical elements: To sum up all the elements’ values.

Assignment of weight value: Arsenic: 5;Fluoride: 3; Iron, Manganese: 1.

Grades of groundwater quality: Good;relatively good; average; below average; poor.Table 1 shows grades of groundwater quality.

Table 1 Grades of groundwater quality

1.4 Standards of groundwater chemical elements

Standards of groundwater chemical elements are referred to WTO’s Drinking Water Quality Standards (WHO, 2005), and the hygiene standards of drinking water in the People’s Republic of China (China State Bureau of Quality and Technical Supervision, 1994, 2006).

(1) TDS

WTO’s standard concentration of TDS is 1 g/L,while Chinese standard is 2 g/L. The taste of water becomes certainly unpleasant with TDS greater than 1 g/L, and the situation would be worse as the TDS gets higher. The Groundwater saltiness is divided into four levels based on TDS’ standard(Table 2): Fresh water, ≤1 g/L; slight brackish water, 1-3 g/L; brackish water, 3-5 g/L; and salt water, >5 g/L (Table 2).

Table 2 Salinity classified standards

(2) Fluoride

WTO’s standard concentration of fluoride is 1.5 mg/L, while China’s standard is 1 mg/L.Fluoride which can be detected easily in the natural water, is one of necessary microelements for human beings. The threshold of fluoride in drinking water is 0.5-1.0 mg/L (Table 3).Groundwater with the concentration of fluoride greater than 1 mg/L is called high-fluoride groundwater. Long-term consumption of highfluoride groundwater will cause endemic fluorosis,nevertheless, the consumption of drinking water with the concentration of fluoride less than 0.5 mg/L for a long term can also lead to disease.

Table 3 Classified standard for concentration of Fluoride

(3) Arsenic

WTO’s standard concentration of arsenic is 0.01 mg/L, while China’s standard is also 0.01 mg/L (Table 4). When the concentration of arsenic in drinking water is greater than 50 μg/L, the water is classified as in a high Arsenic hydrogeochemical environment. The maximum concentration of arsenic in drinking water is 400 μg/L. Considering the limit of monitors, and the assessment for human risk, WTO has reduced the standard of allowable concentration of arsenic in drinking water from 50 μg/L to 10 μg/L. And IARC has assessed the arsenic as one of carcinogens.

Table 4 Classified standard for concentration of Arsenic

(4) Iron &Manganese

WTO’s standard concentrations of iron and manganese are 0.3 mg/L and 0.1 mg/L respectively,while China’s standards are 0.1 mg/L and 0.05 mg/L (Table 5).

In General, elements iron and manganese appear as symbiotic divalent ions in the reductive groundwater environment. If the concentrations of iron and manganese exceed the standard limits,they would have detrimental effects on tastes,washes and the food production.

Table 5 Classified standard for concentrations of iron and manganese

(5) Radon

The upper limit of radioactive 222Rn in groundwater is restricted to 135 Bq/L, due to geological and medical factors. Beyond the limit,the local environment would produce high level of radioactive radon, and a warning sign is required as a high risk area for human health.

2 Groundwater quality distribution and hydrogeochemical characteristics in Asia

The chemical composition and distribution of groundwater is one of the main basis of development and utilization and planning of groundwater resources, and main content of groundwater quality.

Groundwater chemical composition and concentration distribution is in a long development process of geological history, and is the product in the long-term interactions of the environment,natural geography, geologic background and human activities. Therefore, it is performed as the space zonal differentiation (on vertical and horizontal direction) and the temporal fluctuation of succession (CHEN Meng-xiong and MA Feng-shan, 2002).

2.1 Groundwater environment background in Asia

Groundwater environment is influenced due to the significant differences in geographic latitudes and terrains. In the majority region of North Asia,strong continental climate appears between low and middle latitudes of mountains and plateaus(like Tibet Plateau). When combined with the cold current coming from Siberia, and the high pressure in Mongolia, it causes the ground temperature at zero or negative temperature permanently. As a result, the hydrogeochemical effect is not intense,the upside soil is seasonally frozen and thawed,which leads to the damage of rocks, deformation of tundra, and the formation of various landscapes,such as stone river, stone sea, ice mound, and molten subsidence. Nevertheless, in relation of physical changes for groundwater, the water of ice mound is able to make an excellent adjustment upon groundwater runoff, in the region of either low altitudes and high latitudes, or island-shaped frozen zonages, both for a consecutive time, whilst the melting water recharges the quantity of groundwater, especially in the area of island-shaped frozen zonages with high altitudes and low latitudes in Tibet Plateau, also for consecutive periods.

The alternate of water-rock interaction, has greatly influenced the chemical compositions in the groundwater, which is indicated by the change of groundwater quality.

Topographical precipitation has a profound impact upon the water cycle, and groundwater has a strong leaching and migrating effect, which all preserve the water quality at a good standard.Among regions, such as West-Siberian Plain,Huanghuaihai Plain, Song-liao Plain and intermountain basins of difference scales, those semi-humid and semi-arid zones at middle latitudes, the chemical property has a distinguishable distribution between the recharge area in the front and the low-lying region of downstream, whilst the water quality has gradually decreased, which is especially proven by the wide distribution of tertiary gypsum layers and groundwater solute gypsums, as well as the increase of, both in southern Siberia and Central Asia.

In the loess plateau of the Yellow Rivers’middle reaches, deep loess, various types of eroded gully and landscapes in-between gaps (such as tableland, beam, loess hill and pyeong) are formed under the interaction between running water and wind.

Groundwater in loess layers is able to act as recharge and discharge towards the local area, and when considering the short runoff pathways, the salinity of groundwater would depend on the amount of soluble salt in loess. For instance,Kushui River of south Ningxia is formed by the dissolution of sulfuric compounds in its groundwater.

Meanwhile, paleogeographic environment has a significant control towards groundwater vertical zonages. There is salty groundwater sealed up in a distribution area of shallow fresh water, while lens of fresh water, and of brackish water are buried in favorable positions of salty groundwater region,which is vital for local water supply. The Asian climate of vast lands and southwest region is quite arid, as the difference between day and night temperatures is great, physical weathering is frequent, the sand blown by the wind is the main force to shape the terrains in arid area, which forms various types of aeolian sand landform. And as a consequence of water-vapor flux controlled by topography, the water cycle of these regions is sluggish, and evaporation of groundwater is in high speed, leading the concentration of salt in groundwater to be of a high level. Groundwater is generally brackish water with the salt content between 1-3 g/L, and there is salt water whose salt content is greater than 5 g/L in the middle of basins.

In tropical and subtropical regions of Southeast Asian, the climate is hot, rainy and damp, thus, the leaching action and chemical weathering are strong,and thick layer of red weathering crust distributes in a wide range. Rivers are intensive, surface runoff is strong and surface erosion is at a high rate annually (it can reach 3 mm in Java). Rivers are the main contributor to shape drainage basins and topography, forming all kinds of fluvial landform.There is deep limestone layer of Permian and Triassic in Indo-China Peninsula, Yunnan-Guizhou Plateau and Guangxi. Chemical corrosion takes place under the warm and rainy condition, which destroys soluble rocks, and alters them to various types of karst landform. Groundwater cycles are positive, and the leach and the migration of chemical compositions in groundwater are strong.It’s commonly fresh groundwater with the salinity less than 1 g/L. The sea water mixing effect of sea-land alternation within the coastal zone and islands has affected groundwater salinization in coastal region.

2.2 Groundwater hydrogeochemical characteristics in Asia

Groundwater chemical components are in relation to chemical components of crustal rocks and particular characteristics of water.Groundwater participates in the chemical reaction on crustal surface. In this process, different hydrodynamic forces have influenced significantly the formation of chemical components, especially the chemical characteristics of shallow groundwater, which are controlled basically by climate, precipitation, geological and topographical conditions, and have the feature of differentiation between vertical and horizontal zonages (Institute of Hydrogeology and Environmental Geology, 1979; LI Jia-xi and WU Gong-jian, 1999).

In terms of climate and atmospheric precipitation, the climate and landform of Asia control water-vapor flux in mainland, while the complexity of climate types is intensified by the terrain structure of high middle and low around,and vertical and horizontal distributions of large belts, promoting the formation of the typical continental climate and monsoon climate, causing the uneven distribution of spatio-temporal precipitation, forming the decrease trend from southeast of wet to northwest of drought, and Central Asia and West Asia tend to be the most arid desert regions. Special climate and complex vertical climatic zones are formed by plateaus which lead to different relative renewing speed of groundwater in different regions. Groundwater chemical components distribute in zones all around Tibetan-Pamirs, Turan Plain, with southwest of Arabian Peninsula as the center. The distribution is mainly from bicarbonate low mineralized water transitioning to slightly brackish water of heavy carbonate sulfate, then to brackish-salt water of bicarbonate chloride until sulfate-chloride salt water.

Under the control of geological landform,regional horizontal zonage of groundwater’s chemical components is a regular zonal differentiation of groundwater chemical components from mountains to plains and from piedmont to basin center or from mountain front to coast.

There are seven irons widespread and of high content in groundwater, which are Cl-,, Na+, K+, Ca2+and Mg2+. Normally, the TDS changes the main ions in groundwater accordingly., Ca2+and Mg2+are main components in water of low salinity, and Cl-and Na+are main components in groundwater of high salinity, andNa+and Ca2+are main components in groundwater of medium salinity.

The basic characteristic of the groundwater chemical composition in the above five regions is complicated in Asia.

Mountainous areas with bedrock exposed in Asian, are groundwater recharge areas where leaching is the main hydrogeochemical process whist the main hydrochemical type is fresh water of HCO3-Ca (Ca·Mg) or HCO3-Ca·Na.

In regions of arid mountains in Central Asia,the hydrochemical type is complex in regions of desert mountains, the concentration of sulfate is very high in groundwater and groundwater belongs to HCO3·SO4-Na·Mg water.

In most plains or basins and inclined piedmonts,where groundwater runoff area is, water exchanges quite frequently, and leaching is the main hydrogeochemical process, water quality changes with the change of aqueous medium and micro topography, hydrochemical type of groundwater is leached runoff of HCO3-Ca·Mg, HCO3-Na·Mg and HCO3·SO4-Na·Mg.

From central plains to the central coastal low plain and inland basins, groundwater flow rate gradually has weakened to even be stranded.Evaporation and discharge effect are strong.Hydrochemical types are mainly retention of evaporation and concentration effects and sea water mixing effect. Salt concentration gradually raises, which is also reflected by the interbedding of salt water and fresh water. Horizontal variation of hydrogeochemical processes is HCO3·Cl-Na·Mg,SO4·HCO3-Na·Mg, SO4·Cl-Na or brackish-salt water of Cl·HCO3-Na (Na·Mg).

In the coastal region, groundwater is Cl-Na salt water formed by the sea water mixing effect.

2.3 Characteristics of zoning groundwater quality

Condition of groundwater cycles decides the process of leaching desalting and concentrating salinization of groundwater. Groundwater has characteristics of water quality zoning, and its spatial distribution is mainly the result of comprehensive effect of trapezium terrain, the trend of the coastal zone, and the climate from the north and the south to the middle.

Groundwater quality zoning in Asia is led and controlled by climates and topography. The Asian continent which has centered on Pamir-Qinghai-Tibet Plateau, with mountains extending to three sides, crossing cold, warm and hot climatic zones, has a complex climate, which is a typical monsoon climate with significant continental characteristics, and the water vapor sources are coming from the Pacific Ocean, Indian Ocean and Arctic Ocean.

The amount of precipitation has an intimate connection to groundwater recharge, and the abundance of the precipitation plays an important role in leaching-leached effect, meanwhile terrain precipitation also has an enormous impact on the regional water cycle.

Through comprehensive analysis of groundwater chemical types, salinity, precipitation recharge condition and geological environment,Asian groundwater quality zonage is:

Ⅰ- Freshwater zone of bicarbonate type:groundwater salinity is less than 1.0 g/L in most areas (it only can be 1.0-3.0 g/L or greater than 3.0 g/L in local coastal areas);

Ⅱ- Slightly fresh brackish water zone of bicarbonate and sulfate type: groundwater salinity is less than 1.0 g/L in most areas, and it is 1.0-3.0 g/L in some areas (it is greater than 3.0 g/L in local area);

Ⅲ- Brackish water zone of bicarbonate and chloride type: groundwater salinity is 1.0-3.0 g/L or greater than 3.0 g/L in most areas;

Ⅳ- Salt water of sulfate and chloride type:groundwater salinity is 3.0-5.0 g/L or greater than 5.0 g/L in most areas;

Freshwater zone of bicarbonate type: It is distributed in North Asia, northeast of Asia,southeast of Asia and South Asia. Annual precipitation is greater than 400 mm, and it will be 1 000 mm in South Asia. The plentiful precipitation is the sufficient source of groundwater, and groundwater cycles are strong, and leaching and leached are the main influences/effects of groundwater. Climate of South Asia region is between subtropical and tropical monsoon climate,with plentiful precipitation and widespread surface drainage. Physical and chemical weathering of rocks is quite strong, water exchanges frequently,groundwater salinity is nearly less than 1 g/L,which belongs to HCO3-Ca·Na type. Carbonate rocks are widely distributed in Asia, including tropic karst, subtropic karst, temperate karst, frigid karst and karst in drought area. Karst landform distributes unequally with sufficient water.Groundwater chemical composition is HCO3-Ca type in limestone region, and it is HCO3-Ca·Mg type in dolomite region, and groundwater salinity is all less than 1 g/L. The chemical composition concentration is in a relationship of inverse proportional growth/ (or just simply put, is in inverse proportion), with rainfall and spring flow rates. However, in late Paleozoic and Mesozoic salt formation in Sichuan and Yunnan of China,ravines cut by rivers are natural drainage channels of groundwater, where salty water springs with its concentration greater than 2 g/L and salt springs with its concentration greater than 10 g/L, have a significant effect on water chemical composition of local area.

Slightly fresh brackish water zone of bicarbonate and sulfate type: It is mainly distributed in central Arabian Peninsula, central Iran Plateau, north Turan Plain of West Asia,Kazakhstan hilly region, surrounding area of Mongolia Plateau and Qiangtang lakes in Qinghai-Tibet Plateau of Central Asia. The climate of these regions is sub-humid and semi-arid climate, the precipitation normally is 200-400 mm and it decreases to less than 200 mm in Arabian Peninsula and west of Qiangtang region.Precipitation is seasonal uneven, and western area of these regions is partly affected by tropical marine climate while the east part is affected slightly by monsoon climate. Groundwater controlled by semi-arid climate has a gradual transition characteristic, with the groundwater quality turning from fresh water to slightly brackish water. Groundwater chemical types are complex and have obvious regional differences because of the landform and aquifer lithology.Groundwater storage condition is ordinary in middle and lower mountains, hills and plains.Groundwater salinity is mostly 1-3 g/L, and groundwater quality is normal, and the groundwater chemical types are mainly HCO3-Ca·Na type and secondarily HCO3·SO4-Ca(Ca·Mg, Ca·Na) type.

Brackish water zone of bicarbonate and chloride type: it is mainly distributed in Arabian Peninsula desert area, Tigris and Euphrates basins,Iranian Plateau coastal area, central Turan Plain of West Asia, Kazakhstan hilly region, Mongolia Plateau and alluvial fan plain of river estuary in Central Asia. Groundwater of plain areas is affected by micro-relief and aquifer lithology, in low-lying areas or alluvial fan front and paleocurrent interchannel zone. The groundwater runoff is stagnant and groundwater salinity is about 3 g/L under the influence of evaporation concentration. There is a sizable amount of salty water in the late Pleistocene series aquifer of coastal area,and with its thickness and salinity increasing to the coastal areas, there are even greater than 10 g/L type Cl-and Na salt water.

Different geomorphic units are different in their water quality as well. Groundwater quality is better in higher grounds and the edge of river valley or the basin, while groundwater quality gets worse in low-lying or downstream of river valley and central basin area.

Salt water of sulfate and chloride type: It is mainly distributed in Arabian Peninsula desert area,Tigris, Euphrates, Iranian Plateau coastal area,central Turan Plain of West Asia, Kazakhstan hilly region, Mongolia Plateau and alluvial fan plain of river estuary in Central Asia. The precipitation of these regions is normally less than 200 mm, and the climate is typical continental climate, which means that there will be drought, windy and dusty,and extremely hot in summer in desert plains.Reciprocal Transformation between river and groundwater happens under different geological and geomorphic conditions, as groundwater in plains depends mainly on the replenishment of surface water infiltration. Excepting high mountains and piedmont pluvial fan plains, salt groundwater is distributed in most regions. The hydrochemical type is complex, and salinization is strong.

Horizontal chemical zoning presents in inland basins and alternates from the edge of inland basin to the middle. The salification of completely closed basin is stronger, and central basin often has a distribution of mineralized water. Groundwater salinity is much greater than 10 g/L, with the largest up to 200-300 g/L. Salt accumulation in semi-closed basin is relatively low, only local area has a higher salinity of groundwater distributed.

Groundwater in front diluvial fan of piedmont on the inclined plain, gets into the predominantly chloride salt water distribution area through the narrow water transition zone, and groundwater with high salt content is mainly found in Turan Plains, Qaidam, Tarim and Zhungeer inland basins.

2.4 Groundwater quality distribution in Asia

The formation and spatial and temporal distribution of groundwater quality are controlled and affected by climates, geological structures,stratum lithology, topography, hydrological processes and human activities. The groundwater quality has evolved as time goes by. Natural geographical and geological history and human activities affect the chemical feature of groundwater, therefore the inherent basis and pattern of groundwater quality’s evolution must be revealed from the perspective of a long-term interaction between groundwater and environment.Groundwater quality distributes in a larger spatial difference, the trend moves from a high and low latitude to mid-latitude and gradually becomes worse on the whole, and groundwater quality gradually becomes poorer from foothills to the center of basin or from piedmont to coast, and groundwater quality is poor and has complex chemical compositions in delta coastal areas and inland arid zone.

Most areas of North Asia belong to the temperate zone, and north coast and islands in Arctic belong to polar climate. The climate of most regions of North Asia, mountains and plateaus in low and middle latitudes is strong continental climate. Controlled by the Siberian cold current and Mongolia high pressure, it is cold and has weak evaporation there; permanent and seasonal frozen soil is able to be found widely; it is still in a cold and wet environment although the precipitation is low. Precipitation distribution is diminishing from west to east along with the distances towards Atlantic; the west region/area is at about 500 mm rainfall, most of other region is less than 350 mm, whereas as for other region in the northeast, it decreases to 200 mm.Unconsolidated sediments in basin is constructed into blocks by rivers through many river networks,especially in the developing area of a long-term frozen layer. Suprapermafrost water discharges through river valleys and permeable zones, and freezing and thawing alternate actively/positively.In the long-term frozen layer area, groundwater recharges through the adjustment of ice mounds.Infrapermafrost water has the condition to runoff.While in a seasonal frozen layer area, groundwater recharge is influenced significantly by seasonal freezing and thawing, and freezing and thawing alternative area constitutes a good groundwater recharging region. The hydrogeochemical action is not strong in this region, hydrochemical composition is simple, in parts of this region Radon is detected, salinity is basically less than 1 g/L, groundwater geochemical zoning is mainly of bicarbonate type, and groundwater quality is quite good.

East Asia and South Asia belong to tropical and subtropical humid monsoon climate and continental monsoon climate and atmospheric precipitation is mainly affected by warm moist air flows in the Pacific and Indian oceans. The uplift landform of the Qinghai-Tibet Plateau in central Asia controls water vapor flux, and atmospheric precipitation is sufficient for groundwater recharge.Groundwater cycles and alternate effect are strong,and the dissolve and migration effect of hydrochemical composition is at its full action in full motion; the groundwater salinity is low,generally less than 1 g/L, and groundwater quality is good. In coastal zone and the islands of sea-land,the alternation of water mixing effect has a corresponding effect on groundwater salinization of coastal areas, with groundwater salinity generally greater than 3 g/L. Groundwater geochemical zoning is of mainly bicarbonate type and sulfate and chloride type of brackish salt water is in coast and river deltas. Groundwater chemical composition is relatively complex, as radon,fluorine, iron and manganese are widely presented,whilst arsenic distributes widely in the river delta.Most of the groundwater is in a good condition in East Asia and South Asia, but it becomes poor in coastal region, river delta and the island.

Central Asia and West Asia belong to arid and semi-arid climate, and the vast desert basin is surrounded by plateau mountains, whilst the ocean water vapor channels are cut off by tall mountains.Precipitation is mostly less than 200 mm per year,but the amount of evaporation is several times larger than that of rainfall. Precipitation recharge in the desert basin is very scarce, and groundwater is generally supplied by terrain rainfall, which forms a surface runoff and recharges the groundwater. Groundwater cycle and alternative action are sluggish, whilst leaching and migration effect of hydrochemical composition is normal;evaporation and concentration effects are both strong, and groundwater salinity is higher, which is usually 1-3 g/L brackish water and is mostly greater than 5 g/L in the central basin.Groundwater geochemical zoning is mainly of bicarbonate, sulfate and chloride type of slightly brackish-brackish-salt water; groundwater geochemical composition is complicated; there is arsenic distributing in the central basin and river delta, and parts of the region can detect fluorine,radon, manganese and iron. Groundwater quality is generally poor in Central Asia and West Asia, and that of central part of the basin and river delta region is even worse.

3 Conclusions

This map is based on the work of “Mapping of Groundwater Resources and Environmental Geology in China and Surrounding Regions”, and is finished by Institute of Hydrogeology and Environmental Geology of Chinese Academy of Geological Sciences (ZHANG Fa-wang et al.2012). This map has applied the latest research achievements of world and Asian countries, which is the research quintessence of hydrogeological and geological environmental circles. Groundwater and its environment are closely related to the survival and development of mankind. Along with the deepening of the research and the raising the level of understanding, intercontinental series of geological environment compile research remains to be a positive exploration.