Environmental Isotopes Study on Geothermal Water in Guanzhong Basin,Shaanxi Province

There exists abundant thermal water recourses in Guanzhong basin, Shaanxi province (northwestern China). With the deepening of exploitation for thermal aquifer nowadays, the information about the origin and movement of thermal water is limited by using traditional methods. This paper applies environmental isotope techniques to offer direct constraints on the recharge and movement of thermal water and improve the geological and hydrogeological data- base in Guanzhong Basin. The research on the environmental isotopes shows that the geothermal water of the area is mainly recharged by meteoric water. The temperature of meteoric water which replenishes geothermal water in the study area is -16 ℃. The estimated age of recharging the geothermal water is 13.3-28.2 ka based on the isotope analysis, belonging to the last glacial period in Late Quaternary. The source of replenishment of the geothermal water is thought to have been derived from glacial snow-melt water with an elevation higher than 1 500 m (ASL) in the north side of Qinling Mountain. The isotopic analysis denotes that the geothermal water in the southern Guanzhong basin is the mixture of net thermal water and normal temperature groundwater. Based on calculating the percentage of the mixture, nearly half of cold groundwater had participated the circulating of the geothermal water. However, in the center part of the basin, some artificial factors such as mismanage of pumping are probably the reason for the mixturing. The temperature range of the geothermal reservoirs in the basin is estimated at about 80-121 ℃ based on calculation of both SiO2 geothermometer and thermal water saturation index, which are basically in accordance with the measured temperature of thermal water. Based on the replenishment time and mixture extent with cold water, the thermal water in the studied area can be classified into three parts: mixed thermal water replenished by modern meteoric water; mixed thermal water replenished by both modern and ancient meteoric water, and deep circulating thermal water replenished by ancient meteoric water without mixture.

Characterization of groundwater in the Ejina Basin,northwest China:hydrochemical and environmental isotopes approaches

To characterize the groundwater in the Ejina Basin,surface and groundwater samples were collected in May and October of 2002.On-site analyses included temperature,electrical conductance(EC),total alkalinity(as HCO 3) by titration,and pH.Chemical analyses were undertaken at the Geochemistry Laboratory of the Cold and Arid Region Environmental and Engineering Institute,Chinese Academy of Sciences,Lanzhou,China.The pH of the groundwater ranged from 7.18 to 8.90 with an average value of 7.72,indicating an alkaline nature.The total dissolved solids(TDS) of the groundwater ranged from 567.5 to 5,954.4 mg/L with an average of 1,543.1 mg/L and a standard deviation of 1,471.8 mg/L.According to the groundwater salinity classification of Robinove et al.(1958),47.4 percent of the samples were brackish and the remainder were fresh water.The ion concentration of the groundwater along the riverbed and near the southern margin of the basin were lower than those farther away from the riverbed.The groundwater in the study area was of Na +-HCO 3 type near the bank of the Heihe River and in the southern margin of the basin,while Na +-SO 4 2-Cl type samples were observed in the terminal lake region.In the desert area the groundwater reached a TDS of 3,000-6,000 mg/L and was predominantly by a Na +-Cl chemistry.Br/Cl for the water of Ejina Basin indicates an evaporite origin for the groundwater with a strongly depleted Br/Cl ratio(average 0.000484).The surface water was slightly enriched in Br/Cl(average 0.000711) compared with groundwater.The calculated saturation index(SI) for calcite and dolomite of the groundwater samples range from 0.89 to 1.31 and 1.67 to 2.67 with averaged 0.24 and 0.61,respectively.About 97 percent of the groundwater samples were kinetically oversaturated with respect to calcite and dolomite,and all the samples were below the equilibrium state with gypsum.Using isotope and hydrochemical analyses,this study investigated the groundwater evolution and its residence time.The groundwater content was mainly determined by the dissolutions of halite,gypsum,and Glauber’s salt(Na 2 SO 4),as well as Na + exchange for Ca 2+,and calcite and dolomite precipitation.With the exception of a few locations,most of the groundwater samples were suitable for irrigation uses.Most of the stable isotope compositions in the groundwater sampled plotted close to the Global Meteoric Water Line(GMWL),indicating that the groundwater was mainly sourced from meteoric water.There was evidence of enrichment of heavy isotopes in the groundwater due to evaporation.Based on the tritium content in atmospheric precipitation and by adopting the exponential-piston model(EPM),the mean residence time of the unconfined aquifer groundwater was evaluated.The results show that these groundwaters have low residence time(12 to 48 years) and are renewable.In contrast,the confined groundwater had 14 C ages estimated by the Pearson model between 4,087 to 9,364 years BP.Isotopic signatures indicated formation of deep confined groundwaters in a colder and wetter climate during the late Pleistocene and Holocene.

Environmental Isotopes and Cl/Br Ratios Evidences for Delineating Arsenic Mobilization in Aquifer System of the Jianghan Plain,Central China

Environment isotopes(δ18O andδ2H)and Cl/Br ratios in surface water and groundwater are combined to investigate arsenic mobilization in aquifer system of the Jianghan Plain.The groundwater has relatively high arsenic concentrations,ranging from 3.6 to 1055.3μg/L with an average of 102.2μg/L,which exceeds China’s drinking water standard(10μg/L).The arsenic content of surface water samples is quite low with the range of 6.0–14.3μg/L,averaging 9.5μg/L.δ18O andδ2H values for surface water and groundwater samples plot close to the local meteoric water line(LMWL),reflecting their meteoric origin;a subset of the samples(shallow wells,10 m)shows a shift to LMWL,commensurate with mixing with surface water and evaporation.The correlations betweenδ18O values and Cl concentration and Cl/Br ratios as well as arsenic concentration demonstrated that surface water and groundwater interactions,including active exchange between river/pond water and groundwater and vertical infiltration from agricultural and aquacultural soils,were dominated processes affecting arsenic mobilization in shallow groundwater system and lateral recharge was the main process controlling arsenic behavior in deep groundwater system.The results of this study will be beneficial to understanding the causes of arsenic mobilization in Jianghan groundwaters at different depths.

Environmental Isotopic Characterization of Groundwater and Surface Water in Northeast Missan Province,South Iraq

The present work studies the environmental isotopes assess groundwater characteristics of the different parts of the main aquifer in the northeast Missan Province in south of Iraq. Water samples of groundwater and surface water were collected for two dry and wet seasons during the water year of 2011-2012. The study shows that most of the groundwater in the aquifer falls above the global meteoric water line, and all the samples fall below the Mediterranean meteoric water line, indicating that these samples are a mixture of two water types. The tritium content of these samples supports this conclusion. The overall conclusion of this study indicates that there are two sources of groundwater recharge in the studied area： the ephemeral streams （Teeb and Dewerge） and major precipitation sources. According to the tritium levels at or below one tritium unit （TU） obtained from the water, supply wells are highly confined or ＂not vulnerable＂. Overall, the 3^H results imply that recent recharge has taken place during the last four to five decades. In the recharge area, the high tritium content in the southern part of the Teeb area suggests that the recharge originates from rapid infiltration of surface runoff. Therefore, the groundwater resources in the study area should be protected from contamination, because it will influence the aquifer in a relatively short period of time if any contamination enters the recharge areas of the aquifer.

Groundwater hydrochemistry and isotope geochemistry in the Turpan Basin, northwestern China

The Turpan Basin is located in the arid zone of northwestern China and is a typical closed inland basin surrounded by high mountains. It is one of the most arid regions in the world and, as a result, the groundwater in this area is very important for both domestic and agricultural uses. In the present study, the relationships of major elements（K＋, Na＋, Ca2＋, Mg2＋, HCO3-, SO42- and Cl-） and environmental isotopes（δ18O, δ2H and T） in groundwater were analyzed to investigate the evolution of the regional hydrochemistry within the Turpan Basin. The hydrochemistry results demonstrate that groundwater with high total dissolved solids（TDS） concentration is dominated by sodium chloride（Na-Cl） and sodium sulfate（Na-SO4） type water, whereas that with low TDS concentration（typically from near mountain areas） is dominated by calcium bicarbonate（Ca-HCO3） type water. The evolution of groundwater hydrochemistry within the Turpan Basin is a result of calcium carbonate precipitation, evaporation concentration, cation exchange and dissolution of evaporites（i.e. halite, mirabilite and gypsum）. Furthermore, evaporite dissolution associated with irrigation practice plays a key role in the groundwater salinization, especially in the central part of the basin. Environmental isotopes reveal that the groundwater is recharged by precipitation in the mountain areas and fast vertical infiltration of irrigation return flow. In the southern sub-basin the shallow groundwater and the deep groundwater is separated at a depth of about 40 m, with substantial differences in terms of hydrochemical and isotopic characteristics. The results are useful for decision making related to sustainable water resource utilization in the Turpan Basin and other regions in northwestern China.

Determining the groundwater basin and surface watershed boundary of Dalinuoer Lake in the middle of Inner Mongolian Plateau,China and its impacts on the ecological environment

The surface watershed and groundwater basin have fixed recharge scale,which are not only the basic unit for hydrologic cycle research but also control the water resources formation and evolution and its corresponding eco-geological environment pattern.To accurately identify the boundary of the surface watershed and groundwater basin is the basis for properly understanding hydrologic cycle and conducting the water balance analysis at watershed scale in complicated geologic structure area,especially when the boundary are inconsistent.In this study,the Dalinuoer Lake located in the middle of the Inner Mongolian Plateau which has complicated geologic structure was selected as the representative case.Based on the multidisciplinary comprehensive analysis of topography,tectonics,hydrogeology,groundwater dynamics and stable isotopes,the results suggest the following:(1)The surface watershed ridge and groundwater basin divide of Dalinuoer Lake are inconsistent.The surface watershed was divided into two separate groundwater systems almost having no groundwater exchange by the SW-NE Haoluku Anticlinorium Fault which has obvious water-blocking effect.The surface drainage area of Dalinuoer Lake is 6139 km^(2).The northern regional A is the Dalinuoer Lake groundwater system with an area of 4838 km^(2),and the southern regional B is the Xilamulun Riverhead groundwater system with an area of 1301 km^(2).(2)The groundwater in the southern of regional A and the spring-feeding river are the important recharge sources for the Dalinuoer Lake,and it has greater recharge effects than the northern Gonggeer River system.(3)It is speculated that the trend of Haoluku Anticlinorium Fault is the boundary of the westerlies and the East Asian summer Monsoon(EASM)climate systems,which further pinpoints the predecessor’s understanding of this boundary line.At present,the Dalinuoer Lake watershed is proved to have gone through a prominent warming-drying trend periods,which leads to the precipitation reduction,temperature rise,human activities water usage increasement.So the hydrological cycle and lake eco-environment at watershed scale will still bound to be change,which may pose the potential deterioration risk on the suitability of fish habitat.The results can provide basic support for better understanding water balance evolution and lake area shrinkage cause as well as the ecological protection and restoration implementation of Dalinuoer Lake watershed.

Impacts of Human Activities on the Occurrence of Groundwater Nitrate in an Alluvial Plain: A Multiple Isotopic Tracers Approach

Nitrate pollution is a severe problem in areas with intensive agricultural activities. This study focuses on nitrate occurrence and its constraints in a selected alluvial fan using chemical data combined with environmental isotopic tracers （180, 3H, and lSN）. Results show that groundwater nitrate in the study area is as high as 258.0 mg/L （hereafter NO3） with an average of 86.8 mg/L against national drinking water limit of 45 mg/L and a regional baseline value of 14.4 mg/L. Outside of the riparian zone, nitrate occurrence is closely related to groundwater circulation and application of chemical fertilizer.High groundwater nitrate is found in the re- charge area, where nitrate enters into ground- water through vertical infiltration, correspond- ing to high 3H and enriched 1SO in the water. In the riparian zone, on the contrary, the fate of groundwater nitrate is strongly affected by groundwater level. Based on two sampling tran- sects perpendicular to the riverbank, we found that the high level of nitrate corresponds to the deeper water table （25 m） near the urban center, where groundwater is heavily extracted.Groundwater nitrate is much lower （〈12.4 mg/L） at localities with a shallow water table （5 m）, which is likely caused by denitrification in the aquifer.