## 2021 Vol.4(3)

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2021, 4(3): 0-0.
[Abstract](61) [FullText HTML] (54) [PDF 409KB](25)
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2021, 4(3): 1-2.
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2021, 4(3): 377-388. doi: 10.31035/cg2021053
[Abstract](278) [FullText HTML] (211) [PDF 5040KB](59)
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Delingha is located in the northeast margin of Qaidam Basin. Bayin River alluvial proluvial fan is the main aquifer of Delingha, in which groundwater generally flows from north to south. The hydrochemistry results showed that two different hydrochemical evolution paths formed along southeast and southwest directions, respectively. Cl-Na type groundwater was formed in front of Gahai Lake, and SO4·HCO3-Na·Ca type groundwater was formed in front of Keluke Lake. The results of deuterium (D) and 18O revealed that the groundwater mainly originated from the continuous accumulation of precipitation during geological history under cold and humid climate conditions. In addition, results of 14C indicated that the groundwater age was more than 1140 years, implying relatively poor renewal capability of regional groundwater. Moreover, our numerical modeling results showed that the regional groundwater level will continue to rise under the warm and humid climate conditions.
2021, 4(3): 389-401. doi: 10.31035/cg2021055
[Abstract](229) [FullText HTML] (177) [PDF 3738KB](53)
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Glaciers are crucial water resources for arid inland rivers in Northwest China. In recent decades, glaciers are largely experiencing shrinkage under the climate-warming scenario, thereby exerting tremendous influences on regional water resources. The primary role of understudying watershed scale glacier changes under changing climatic conditions is to ensure sustainable utilization of regional water resources, to prevent and mitigate glacier-related disasters. This study maps the current (2020) distribution of glacier boundaries across the Kaidu-Kongque river basin, south slope of Tianshan Mountains, and monitors the spatial evolution of glaciers over five time periods from 2000–2020 through thresholded band ratios approach, using 25 Landsat images at 30 m resolution. In addition, this study attempts to understand the role of climate characteristics for variable response of glacier area. The results show that the total area of glaciers was 398.21 km2 in 2020. The glaciers retreated by about 1.17 km2/a (0.26%/a) from 2000 to 2020.The glaciers were reducing at a significantly rapid rate between 2000 and 2005, a slow rate from 2005 to 2015, and an accelerated rate during 2015–2020. The meteorological data shows slight increasing trends of mean annual temperature (0.02°C/a) and annual precipitation (2.07 mm/a). The correlation analysis demonstrates that the role of temperature presents more significant correlation with glacier recession than precipitation. There is a temporal hysteresis in the response of glacier change to climate change. Increasing trend of temperature in summer proves to be the driving force behind the Kaidu-Kongque basin glacier recession during the recent 20 years.
2021, 4(3): 402-409. doi: 10.31035/cg2021064
[Abstract](209) [FullText HTML] (151) [PDF 5778KB](31)
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To identify the response of groundwater level variation to global climate change in Northwest China’s inland basins, the Golmud River Catchment was chosen as a case in this paper. Approaches of time series analysis and correlation analysis were adopted to investigate the variation of groundwater level influenced by global climate change from 1977 to 2017. Results show that the temperature in the Golmud River Catchment rose 0.57°C every 10 years. It is highly positive correlated with global climate temperature, with a correlation coefficient, 0.87. The frequency and intensity of extreme precipitation were both increased. Generally, groundwater levels increased from 1977 to 2017 in all phreatic and confined aquifers and the fluctuation became more violent. Most importantly, extreme precipitation led to the fact that groundwater level rises sharply, which induced city waterlogging. However, no direct evidence shows that normal precipitation triggered groundwater level rise, and the correlation coefficients between precipitation data from Golmud meteorological station located in the Gobi Desert and groundwater level data of five observation wells are 0.13, 0.02, −0.11, 0.04, and −0.03, respectively. This phenomenon could be explained as that the main recharge source of groundwater is river leakage in the alluvial-pluvial Gobi plain because of the high total head of river water and goodness hydraulic conductivity of the vadose zone. Data analysis shows that glacier melting aggravated because of local temperature increased. As a result, runoff caused groundwater levels to ascend from 1977 to 2017. Correlation coefficients of two groundwater wells observation data and runoff of Golmud River are 0.80 and 0.68. The research results will contribute to handling the negative effects of climate change on groundwater for Northwestern China.
2021, 4(3): 410-420. doi: 10.31035/cg2021052
[Abstract](202) [FullText HTML] (139) [PDF 3490KB](32)
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Quantitative assessment of the impact of groundwater depletion on phreatophytes in (hyper-) arid regions is key to sustainable groundwater management. However, a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking. A variable saturated flow model, HYDRUS-1D, was used to numerically assess the influences of depth to the water table (DWT) and mean annual precipitation (MAP) on transpiration of groundwater-dependent vegetation in (hyper-) arid regions of northwest China. An exponential relationship is found for the normalized transpiration (a ratio of transpiration at a certain DWT to transpiration at 1 m depth, Ta*) with increasing DWT, while a positive linear relationship is identified between Ta* and annual precipitation. Sensitivity analysis shows that the model is insensitive to parameters, such as saturated soil hydraulic conductivity and water stress parameters, indicated by an insignificant variation (less than 20% in most cases) under ± 50% changes of these parameters. Based on these two relationships, a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for (hyper-) arid regions using MAP only. The estimated Ta* from the model is reasonable by comparing with published measured values.
2021, 4(3): 421-432. doi: 10.31035/cg2021056
[Abstract](178) [FullText HTML] (123) [PDF 3813KB](38)
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The Badain Jaran Desert is the third largest desert in China, covering an area of 50000 km2. It lies in Northwest China, where the arid and rainless natural environment has a great impact on the climate, environment, and human living conditions. Based on the results of 1∶250000 regional hydrogeological surveys and previous researches, this study systematically investigates the circulation characteristics and resource properties of the groundwater as well as the evolution of the climate and ecological environment since the Quaternary in the Badain Jaran Desert by means of geophysical exploration, hydrogeological drilling, hydrogeochemistry, and isotopic tracing. The results are as follows. (1) The groundwater in the Badain Jaran Desert is mainly recharged through the infiltration of local precipitation and has poor renewability. The groundwater recharge in the desert was calculated to be 1.8684×108 m3/a using the water balance method. (2) The Badain Jaran Desert has experienced four humid stages since the Quaternary, namely MIS 13-15, MIS 5, MIS 3, and the Early‒Middle Holocene, but the climate in the desert has shown a trend towards aridity overall. The average annual temperature in the Badain Jaran Desert has significantly increased in the past 50 years. In detail, it has increased by about 2.5°C, with a higher rate in the south than in the north. Meanwhile, the precipitation amount has shown high spatial variability and the climate has shown a warming-drying trend in the past 50 years. (3) The lakes in the hinterland of the Badain Jaran Desert continuously shrank during 1973‒2015. However, the vegetation communities maintained a highly natural distribution during 2000‒2016, with the vegetation cover has increased overall. Accordingly, the Badain Jaran Desert did not show any notable expansion in that period. This study deepens the understanding of groundwater circulation and the climate and ecological evolution in the Badain Jaran Desert. It will provide a scientific basis for the rational exploitation of the groundwater resources and the ecological protection and restoration in the Badain Jaran Desert.
2021, 4(3): 433-445. doi: 10.31035/cg2021049
[Abstract](195) [FullText HTML] (119) [PDF 3943KB](19)
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In order to study the hydrodynamic characteristics of the karst aquifers in northern China, time series analyses (correlation and spectral analysis in addition with hydrograph recession analysis) are applied on Baotu Spring and Heihu Spring in Jinan karst spring system, a typical karst spring system in northern China. Results show that the auto-correlation coefficient of spring water level reaches the value of 0.2 after 123 days and 117 days for Baotu Spring and Heihu Spring, respectively. The regulation time obtained from the simple spectral density function in the same period is 187 days and 175 days for Baotu Spring and Heihu Spring. The auto-correlation coefficient of spring water level reaches the value of 0.2 in 34–82 days, and regulation time ranges among 40–59 days for every single hydrological year. The delay time between precipitation and spring water level obtained from cross correlation function is around 56 days for the period of 2012–2019, and varies among 30–79 days for every single hydrological year. In addition, the spectral bands in cross amplitude functions and gain functions are small with 0.02, and the values in the coherence functions are small. All these behaviors illustrate that Jinan karst spring system has a strong memory effect, large storage capacity, noticeable regulation effect, and time series analysis is a useful tool for studying the hydrodynamic characteristics of karst spring system in northern China.
2021, 4(3): 446-454. doi: 10.31035/cg2021059
[Abstract](157) [FullText HTML] (119) [PDF 3360KB](6)
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Seasonal frozen soil accounts for about 53.50% of the land area in China. Frozen soil is a complex multiphase system where ice, water, soil, and air coexist. The distribution and migration of salts in frozen soil during soil freezing are notably different from those in unfrozen soil areas. However, little knowledge is available about the process and mechanisms of salt migration in frozen soil. This study explores the mechanisms of salt migration at the ice-liquid interface during the freezing of pore fluids through batch experiments. The results are as follows. The solute concentrations of liquid and solid phases at the ice-liquid interface (\begin{document}${C}_{L}^{*}$\end{document}, \begin{document}${C}_{S}^{*}$\end{document}) gradually increased at the initial stage of freezing and remained approximately constant at the middle stage. As the ice-liquid interface advanced toward the system boundary, the diffusion of the liquid phase was blocked but the ice phase continued rejecting salts. As a result, \begin{document}${C}_{L}^{*}$\end{document} and \begin{document}${C}_{S}^{*}$\end{document} rapidly increased at the final stage of freezing. The distribution characteristics of solutes in ice and the liquid phases before \begin{document}${C}_{L}^{*}$\end{document} and \begin{document}${C}_{S}^{*}$\end{document} became steady were mainly affected by the freezing temperature, initial concentrations, and particle-size distribution of media (quartz sand and kaolin). In detail, the lower the freezing temperature and the better the particle-size distribution of media, the higher the solute proportion in the ice phase at the initial stage of freezing. Meanwhile, the increase in concentration first promoted but then inhibited the increase of solutes in the ice phase. These results have insights and scientific significance for the tackling of climate change, the environmental protection of groundwater and soil, and infrastructure protection such as roads, among other things.
2021, 4(3): 455-462. doi: 10.31035/cg2021060
[Abstract](218) [FullText HTML] (121) [PDF 5124KB](13)
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The Luanhe River Delta is located in the center of the Circum-Bohai Sea Economic Zone. It enjoys rapid economic and social development while suffering relatively water scarcity. The overexploitation of groundwater in the Luanhe River Delta in recent years has caused the continuous drop of groundwater level and serious environmental and geological problems. This study systematically analyzes the evolution characteristics of the population, economy, and groundwater exploitation in the Luanhe River Delta and summarizes the change patterns of the groundwater flow regime in different aquifers in the Luanhe River Delta according to previous water resource assessment data as well as the latest groundwater survey results. Through comparison of major source/sink terms and groundwater resources, the study reveals the impacts of human activities on the groundwater resources and ecological environment in the study area over the past 30 years from 1990 to 2020. The results are as follows. The average annual drop rate of shallow groundwater and the deep groundwater in the centers of depression cones is 0.4 m and 1.64 m, respectively in the Luanhe River Delta in the past 30 years. The depression cones of shallow and deep groundwater in the study area cover an area of 545.32 km² and 548.79 km², respectively, accounting for more than 10% of the total area of the Luanhe River Delta. Overexploitation of groundwater has further aggravated land subsidence. As a result, two large-scale subsidence centers have formed, with a maximum subsidence rate of up to 120 mm/a. The drop of groundwater level has induced some ecological problems in the Luanhe River Delta area, such as the zero flow and water quality deterioration of rivers and continuous shrinkage of natural wetlands and water. Meanwhile, the proportion of natural wetland area to the total wetland area has been decreased from 99% to 8% and the water area from 1776 km² to 263 km². These results will provide data for groundwater overexploitation control, land subsidence prevention, and ecological restoration in plains and provide services for water resources management and national land space planning.
2021, 4(3): 463-475. doi: 10.31035/cg2021054
[Abstract](202) [FullText HTML] (132) [PDF 3016KB](20)
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Ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and anaerobic ammonia-oxidation (anammox) bacteria are very important contributors to nitrogen cycling in natural environments. Functional gene abundances of these microbes were believed to be well relevant to N-cycling in groundwater systems, especially in the Pearl River Delta (PRD) groundwater with unique high intrinsic ammonia concentrations. In this research, 20 sediment samples from two in the PRD were collected for porewater chemistry analysis and quantification of N-cycling related genes, including archaeal and bacterial amoA gene and anammox 16S ribosomal Ribonucleic Acid (rRNA) gene. Quantitative Polymerase Chain Reaction (qPCR) results showed that gene abundances of AOA, AOB, and anammox bacteria ranged from 3.13×105 to 3.21×107, 1.83×104 to 2.74×106, and 9.27×104 to 8.96×106 copies/g in the sediment of the groundwater system, respectively. Anammox bacteria and AOA dominated in aquitards and aquifers, respectively, meanwhile, the aquitard-aquifer interfaces were demonstrated as ammonium-oxidizing hotspots in the aspect of gene numbers. Gene abundances of nitrifiers were analyzed with geochemistry profiles. Correlations between gene numbers and environmental variables indicated that the gene abundances were impacted by hydrogeological conditions, and microbial-derived ammonium loss was dominated by AOA in the northwest PRD and by anammox bacteria in the southeast PRD.
2021, 4(3): 476-486. doi: 10.31035/cg2021058
[Abstract](185) [FullText HTML] (116) [PDF 4153KB](17)
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The groundwater level has been continuously decreasing due to climate change and long-time overexploitation in the Xiong ’an New Area, North China, which caused the enhanced mixing of groundwater in different aquifers and significant changes in regional groundwater chemistry characteristics. In this study, groundwater and sediment pore-water in drilling cores obtained from a 600 m borehole were investigated to evaluate hydrogeochemical processes in shallow and deep aquifers and paleo-environmental evolution in the past ca. 3.10 Ma. Results showed that there was no obvious change overall in chemical composition along the direction of groundwater runoff, but different hydrochemical processes occurred in shallow and deep groundwater in the vertical direction. Shallow groundwater (< 150 m) in the Xiong ’an New Area was characterized by high salinity (TDS > 1000 mg/L) and high concentrations of Mn and Fe, while deep groundwater had better water quality with lower salinity. The high TDS values mostly occurred in aquifers with depth < 70 m and >500 m below land surface. Water isotopes showed that aquifer pore-water mostly originated from meteoric water under the influence of evaporation, and aquitard pore-water belonged to Paleo meteoric water. In addition, the evolution of the paleoclimate since 3.10 Ma BP was reconstructed, and four climate periods were determined by the δ18O profiles of pore-water and sporopollen records from sediments at different depths. It can be inferred that the Quaternary Pleistocene (0.78‒2.58 Ma BP) was dominated by the cold and dry climate of the glacial period, with three interglacial intervals of warm and humid climate. What’s more, this study demonstrates the possibilities of the applications of pore-water on the hydrogeochemical study and further supports the finding that pore-water could retain the feature of paleo-sedimentary water.
2021, 4(3): 487-497. doi: 10.31035/cg2021051
[Abstract](194) [FullText HTML] (124) [PDF 3378KB](10)
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This study aims to investigate the mechanisms and health risks of fluoride enrichment in groundwater in the Loess Plateau, China. By taking Dali County, Shaanxi Province, China as an example, this study obtains the following results through field investigation and the analyses of water, soil, and crop samples. (1) The groundwater can be divided into two major types, namely the Quaternary pore-fissure water and Karst water. The Karst area and sandy area have high-quality groundwater and serve as the target areas for optional water supply. The groundwater in the study area is slightly alkaline and highly saline. Meanwhile, high-fluoride groundwater is mainly distributed in the loess and river alluvial plains in the depression area of the Guanzhong Basin and the discharge areas of the groundwater, with the highest fluoride concentration exceeding seven times the national standard. (2) Fluoride in groundwater mainly originates from a natural source and human activities. The natural source refers to the fluoride-bearing minerals in rocks and soil, and the fluoride from this source is mainly controlled by natural factors such as climate, geologic setting, pH, specific hydrochemical environment, ion exchange, and mineral saturation. Human activities in modern life can be further divided into industrial and agricultural sources primarily. (3) The health risks of fluoride contamination are very high in the Loess Plateau, especially for children compared to adults. Meanwhile, the risks of fluoride exposure through food intake are higher than those through drinking water intake. The authors suggest selecting target areas to improve water supply and ensure the safety of drinking water in the study area. Besides, it is necessary to plant crops with low fluoride content or cash crops and to conduct groundwater treatment to reduce the fluoride concentration in drinking water. These results will provide a theoretical basis for safe water supply in the faulted basin areas in the Loess Plateau.
2021, 4(3): 498-508. doi: 10.31035/cg2021066
[Abstract](188) [FullText HTML] (82) [PDF 14732KB](18)
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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 km2. The northern regional A is the Dalinuoer Lake groundwater system with an area of 4838 km2, and the southern regional B is the Xilamulun Riverhead groundwater system with an area of 1301 km2. (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.
2021, 4(3): 509-526. doi: 10.31035/cg2021057
[Abstract](158) [FullText HTML] (67) [PDF 5623KB](22)
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The fresh groundwater in the Loess Plateau serves as a major source of water required for the production and livelihood of local residents and is greatly significant for regional economic and social development and ecological protection. This paper analyzes the hydrogeological conditions and groundwater characteristics in the Loess Plateau, expatiates on the types and distribution characteristics of the fresh groundwater in the plateau, and analyzes the influencing factors and mechanisms in the formation of the fresh groundwater in the plateau as a priority. Based on this, it summarizes the impacts of human activities and climatic change on the regional fresh groundwater. The groundwater in Loess Plateau features uneven temporal-spatial distribution, with the distribution space of the fresh groundwater closely relating to precipitation. The groundwater shows a distinct zoning pattern of hydrochemical types. It is fresh water in shallow parts and is salt water in deep parts overall, while the fresh water of exploration value is distributed only in a small range. The storage space and migration pathways of fresh groundwater in the loess area feature dual voids, vertical multilayers, variable structure, poor renewability, complex recharge processes, and distinct spatial differences. In general, the total dissolved solids (TDS) of the same type of groundwater tends to gradually increase from recharge areas to discharge areas. Conditions favorable for the formation of fresh groundwater in loess tablelands include the low content of soluble salts in strata, weak evaporation, and special hydrodynamic conditions. Owing to climate change and human activities, the resource quantity of regional fresh water tends to decrease overall, and the groundwater dynamic field and the recharge-discharge relationships between groundwater and surface water have changed in local areas. Human activities have a small impact on the water quality but slightly affect the water quantity of the groundwater in loess.
2021, 4(3): 527-535. doi: 10.31035/cg2021062
[Abstract](156) [FullText HTML] (61) [PDF 3250KB](22)
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At present, investigation about the relationship between the change of groundwater level and vegetation mostly focuses on specific watersheds, i.e. limited in river catchment scale. Understanding the change of groundwater level on vegetation in the basin or large scale, be urgently needed. To fill this gap, two typical arid areas in the west of China (Tarim Basin and Qaidam Basin) were chosen the a typical research area. The vegetation status was evaluated via normalization difference vegetation index (NDVI) from 2000 to 2016, sourced from MODN1F dataset. The data used to reflect climate change were download from CMDSC (http://data.cma.cn). Groundwater level data was collected from monitor wells. Then, the relationship of vegetation and climate change was established with univariate linear regression and correlation analysis approach. Results show that: Generally, NDVI value in the study area decreased before 2004 then increased in the research period. Severe degradation was observed in the center of the basin. The area with an NDVI value > 0.5 decreased from 12% to 6% between 2000 and 2004. From 2004 to 2014, the vegetation in the study area was gradually restored. The whole coverage of Qaidam Basin was low. And the NDVI around East Taigener salt-lake degraded significantly, from 0.596 to 0.005, 2014 and 2016, respectively. The fluctuation of groundwater level is the main reason for the change of surface vegetation coverage during the vegetation degradation in the basin. However, the average annual precipitation in the study area is low, which is not enough to have a significant impact on vegetation growth. The annual average precipitation showed an increase trend during the vegetation restoration in the basin, which alleviates the water shortage of vegetation growth in the region. Meanwhile, the dependence of surface vegetation on groundwater is obviously weakened with the correlation index is −0.248. The research results are of some significance to eco-environment protection in the arid area of western China.
2021, 4(3): 536-538. doi: 10.31035/cg2021063
[Abstract](141) [FullText HTML] (65) [PDF 3053KB](7)
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