Hydrogeological Functioning of a Karst Underground River Basin in Southwest China.

The Maocun underground karst river system in the peak cluster depression is an important source of groundwater in southwest China. Multitracers and high resolution water-level-monitoring technology were used to assess and evaluate the hydrogeological structure and flow dynamics. The results showed that the spatial geological structures of the sites had high heterogeneity. Scatter plots of environmental tracers divided the sampling points into groups under different water flow patterns. The karstification was found to increase from sites XLB and LLS to sites BY, SGY and BDP to sites CY and DYQ, where the main water flow patterns at these site groups were diffuse water, both diffuse water and conduit water, and conduit water, respectively. The response times of the subsystems were found to be influenced by the spatial structure, the degree of karstification, and the volume of precipitation and frequency. The average response times of SGY, BDP, ZK, and Outlet in the selected precipitation scenarios were 5.17, 4.08, 16.42, and 5.83 h, respectively. In addition, the EC, δ13 CDIC , 222 Rn, and δ18 O exhibited both linear or exponential relationships. Overall, three hydrogeological conceptual models were constructed showing: (1) high precipitation driving the deep water, resulting in a concentrated flow regime and regional groundwater flow field; (2) both concentrated and diffuse water flows existing under moderate precipitation, resulting in mixed water flow field; (3) the water cycle in the shallow karst aquifer system under low precipitation causing the local groundwater flow field to be dominated by diffuse water flow.

[Evaluation of Heavy Metal Content, Sources, and Potential Ecological Risks in Soils of Southern Hilly Areas].

In order to explore the characteristics of soil heavy metal pollution and ecological risk status in southern hilly areas, a hilly area of a southern province was selected as the research area, using soil samples collected at 60 points in 2017. The single factor pollution index (Pi), Nemero comprehensive pollution index, and potential ecological risk index (RI) were used to evaluate the content characteristics and potential ecological risks of eight heavy metal elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn), and positive definite matrix factor analysis models (PMF) were used to analyze their sources of pollution. The results were as follows:① the content of eight heavy metal elements in the study area exceeded the standard, and the Nemeiro comprehensive pollution index showed that the proportions of light, moderate, and heavy pollution in the study area were 63%, 8%, and 2%, respectively. Unpolluted and lightly polluted samples accounted for 27% and were thus basically lightly polluted. ②The comprehensive potential ecological risk index showed that the RI of soil heavy metals was 39.58-224.15, the proportions of samples with low and medium ecological risks were 73.33% and 25%, respectively, and the proportion of sites with severe ecological risks was 1.67%. Although this site had the highest ecological risk, the content of heavy metals was lower than the background value of soil elements in the province. ③Six pollution sources were obtained through the PMF model:natural sources, agricultural activity sources, mixed sources composed of copper mining and transportation, industrial activity sources, transportation sources, and domestic waste emission sources. The contribution rates of each source were 24.8%, 17.7%, 17.7%, 17.6%, 12.0%, and 10.2%, respectively.

[Water Chemical Characteristics and Influence of Exogenous Acids in the Yangtze River Basin].

To explore the influence of human activities on the Yangtze River water chemistry, water samples were obtained from a representative section the main river stem/branch in wet and normal seasons in 2016. Ion ratio analysis, principal component analysis(PCA), and chemical ion balance calculations were performed, and carbonate rock dissolution rates were determined based on carbonate and exogenous acids. The result show that HCO3-Ca is the dominant hydrochemistry type, indicating that the dissolution of carbonate rocks in the basin is the main process affecting hydrochemistry, and carbonate acid is significant in the weathering of carbonate rocks. In addition, the proportion of carbonate acid dissolution in the wet and normal seasons accounted for 60.33% and 59.14% of the total dissolution, respectively. The dissolution ratio among the different sampling points was notable, which indicates that the carbon sink effect of exogenous acid cannot be ignored. In addition, cation exchange some influence on hydrochemistry but was not the main reaction process. Compared with hydrological monitoring data for the last few years, the weathering of rocks by sulfuric and nitrate acids has strengthened, and the negative effects of anthropogenic pollution in the Yangtze River have increased.

Dynamics in riverine inorganic and organic carbon based on carbonate weathering coupled with aquatic photosynthesis in a karst catchment, Southwest China.

Carbonate mineral weathering coupled with aquatic photosynthesis, herein termed 'coupled carbonate weathering' (CCW), represents a significant carbon sink which is determined by riverine hydrochemical variations. The magnitudes, variations and mechanisms responsible for the carbon sink produced by CCW are still unclear. In this study, major ions, TOC and discharge data at the Darongjiang, Lingqu, Guilin and Yangshuo hydrologic stations in Li River basin, a karst catchment typical of this geographic region, were analysed from January 2012 to December 2015 to elucidate the temporal variations in riverine inorganic and organic carbon and their controlling mechanisms. The results show that (1) HCO3- was sourced from carbonate weathering and silicate weathering, carbonate weathering by carbonic acid being predominant; (2) TOC was created chiefly by the transformation of bicarbonate to organic carbon by aquatic phototrophs during the non-flood period; (3) The carbon sink produced by coupled carbonate weathering in the Li River basin was calculated to be 14.41 tC·km-2·yr-1, comprised of the sink attributable to carbonate weathering (12.17 tC·km-2·yr-1) and sink due to the "biological carbon pump" (SBCP) (2.24 tC·km-2·yr-1). The SBCP thus accounted for approximately 15.54% of the total carbon sink, indicating that the proportion of riverine TOC sourced by the transformation from bicarbonate to organic carbon by aquatic phototrophs may be high and must be considered in the estimation of carbonate weathering-related carbon sinks elsewhere.

[Dynamic Changes in Hydrochemical Characteristics and Influencing Factors in the Karst Watershed Flood Process].

The hydrochemistry of river water in a karst basin has a rapid response to the rainstorm/flood process, which is an important process of the karst carbon cycle and should not be ignored. Based on the dynamic monitoring of the hydrochemical characteristics of the flood process in the Yangshuo section on November 8-12, 2015, the dynamic change in the main ions and the influencing factors were analyzed, and the concentration and flux of inorganic carbon from different sources were calculated. The results showed that the hydrochemistry types in different stages of the flood area belonged to the Ca-HCO3 type. The ions were mainly sourced from carbonate weathering, and affected by silicate weathering, rainfall, and human activities. Because of the hydrological process, the weathering strength of carbonate rocks sharply weakened at the beginning of the flood, and then gradually increased. The concentrations of HCO3-, Ca2+, and Mg2+ sharply decreased at the beginning of the flood, then gradually increased, and continued to increase in the second flood process because of the waterlogging in the karst system. Because of the waterlogging, the reaction time between water and rock become longer; thus, the concentrations are higher. The dynamic changes in SO42-, Cl-, Na+, and K+ were mainly affected by precipitation and human activities. At the beginning of the flood, the concentrations of SO42-, Cl-, Na+, and K+ increased because the runoff takes more ions sourced from activities. The concentrations of SO42-, Cl-, Na+, and K+ decreased with the decrease of easily transported substances. At the lowest point of concentration, SO42- and Cl- were mainly sourced from precipitation, and Na+ and K+ were mainly sourced from precipitation and silicate weathering. The weathering of carbonates by carbonic acid was the main source of inorganic carbon, accounting for 74.3% of total inorganic carbon on average. Because of the input of sulfuric/nitric acid, the contribution of the weathering of carbonates by sulfuric/nitric acid to the inorganic carbon cannot be ignored, and the contribution increased significantly in the flood, up to 31.7%. The geological carbon sinks before the flood, and during the first and second flood processes in the Yangshuo section were 1.28×108, 5.28×108, and 11.52×108 g·d-1, respectively. The geological carbon sink before the flood was equal to the annual average flux, whereas the geological carbon sink in the flood process was several times that of the annual average flux. Moreover, because of the significant difference in the weathering strength of carbonate rocks during the two floods, there was also a significant difference in the amount of geological carbon sink under the same discharge.

Effects of aquatic phototrophs on seasonal hydrochemical, inorganic, and organic carbon variations in a typical karst basin, Southwest China.

Karst processes play an important role in the global carbon cycle. Aquatic phototrophs can transform bicarbonate, which is mainly derived from the weathering of carbonates, into organic carbon. Carbonate mineral weathering coupled with aquatic photosynthesis can be considered a stable and durable carbon sink process. In this study, we addressed seasonal variations in water chemistry in the Lijiang River Basin, which is a typical karst basin, through a comprehensive geochemical study of the river water in four seasons. The parameters were measured in situ, including major ions and isotopes of inorganic and organic carbon. The results showed that (1) DIC was mainly derived from the weathering of carbonates; (2) the transformation from bicarbonate to organic carbon by aquatic phototrophs was evident, and the water chemistry changed, especially in spring and autumn and in the mainstream from Guilin to Yangshuo, which benefited the growth of aquatic phototrophs; and (3) the organic carbon derived from bicarbonates by aquatic phototrophs was nearly half the total organic carbon and 8% of the dissolved inorganic carbon. These results imply that aquatic phototrophs in karst basins can significantly stabilize carbon originating from carbonate rock weathering processes in karst areas.

[Fate and Origin of Major Ions in River Water in the Lhasa River Basin, Tibet].

In order to understand the temporal and spatial variations of major ions in water and their sources in the Lhasa River Basin, water samples were collected monthly at the hydrological station in the Lhasa River from August 2014 to July. The results show that HCO3- is the dominant anion in the water of the Lhasa River, which accounts for 68.73% of the anions, followed by SO42-. Ca2+ is the dominant cation, which accounts for 67.75% of the cations, followed by Mg2+. The pH values of the river water range between 8.31 and 8.90, with a mean of 8.59 throughout the year, generally showing alkaline water. The highest pH values occur in summer, which is probably due to the photosynthesis of aquatic plants and the growth of phytoplankton. Electrical conductivity (EC) varies between 155.0 and 257.0 µS·cm-1, with a mean of 210.5 µS·cm-1. Because of the frequent uplift of the Tibetan Plateau that enhanced the mechanical weathering of rocks and mineral dissolution, the total dissolved solid (TDS) concentration, at an average of 181.35 mg·L-1, is significantly higher than the average value of rivers around the world. The Lhasa River is recharged by surface runoff, so the concentrations of major ions in water are higher during winter, but lower in summer. An ion source analysis indicates that Ca2+, Mg2+, and HCO3- are mainly derived from chemical weathering of carbonate minerals, Cl-, SO42-, and NO3- are mainly affected by precipitation and rock weathering. Furthermore, the concentrations of major ions in the water have a negative correlation with the river discharge rate, which suggests there might be a dilution effect occurring during the rainy season.

[Spatial Variation and Environmental Significance of δ18O and δD Isotope Composition in Xijiang River].

The H and O isotope composition of the Xijiang water was investigated on 54 samples collected from the mainstreams and main tributaries in June 2014 and January 2015.It was found that in the Xijiang river, there was a remarkable linear relationship between δ18 O and δD. This relationship was more significant in the dry season. In both seasons, the 18 O and D values distributed along the meteoric water line, which indicated that precipitation was the source of the Xijiang River. Due to the direct water recharge through karst forms (i.e. sinkholes, vertical shaft and funnel) to the underground river, the d-excess value was higher in the rainy season. While during the dry season, water recharge came from the storage in fissures and pores. Affected by altitude and evaporation effect, along the mainstream Hongshui River-Xunjiang and tributary Youjiang-Yujiang reach, the δ18 O and δD values were gradually approaching positive value in general. However, along the short tributary Guijiang reach, the altitude difference was not dramatic, and the discharge was less, the same phenomenon was not observed. By establishing a linear regression model between δ18 O and altitude, it revealed that the change rate of Xijiang water with altitude was -0.44‰·(100 m)-1 in the rainy season, and -0.45‰·(100 m)-1 in the dry season. The result reflected the height effect of the precipitation, which has a considerable meaning for the study of hydrological cycle in a river basin.

[Endovascular treatment of ruptured aneurysms located at anterior communicating artery complex: a sixty-six cases report].

OBJECTIVE: To investigate the endovascular treatments for the ruptured aneurysms located at anterior communicating artery complex (ACoAC). METHODS: The data of patients with ruptured ACoAC aneurysms treated in Department of Neurosurgery, First Affiliated Hospital to Fourth Military Medical University from May 2013 to December 2014 was retrospectively analyzed. Sixty-six cases were recruited including 50 male and 16 female patients. The patients aged from 31 to 69 years old, averaging (51±8) years. The Hunt-Hess grade at admission were 13 cases with grade Ⅰ, 36 cases with grade Ⅱ, 11 cases with grade Ⅲ, and 6 cases with grade Ⅳ. The most diameter of aneurysms sac: 14 cases less than or equal to 3 mm, 36 cases more than 3 mm but less than or equal to 7 mm, and 16 cases more than 7 mm. The height diameter/neck width ratio: 8 cases with absolute wide neck, 50 cases with relatively wide neck, and 8 cases with narrow neck. There were 28 cases underwent single micro-catheter embolization, 18 cases underwent double micro-catheters embolization, 14 cases underwent stent-assisted embolization and 6 cases underwent balloon-assisted embolization. The patients were followed up for 6 to 12 months and evaluated by modified Rankin score (mRS) and digital subtraction angiography (DSA). The ratio of total embolization, recurrence rate, and time from operation to reexamination of four groups managed by different endovascular treatment were compared by χ(2) test or F test. RESULTS: Sixty cases were totally embolized, 3 cases subtotally embolized, 3 cases incompletely embolized. Mild hemiparalysis and aphasia occurred in 2 cases, and 1 case died of infarction induced by subarachnoid haemorrhage. The mRS at six months after operation were 0 in 31 cases, 1 in 22 cases, 2 in 8 cases, 3 in 2 cases, 4 in 2 cases, 6 in 1 case. All the included cases reexamined the DSA at averaging (7.5±1.0) month post-operatively and 4 cases recurred. There were not significant differences of the ratio of total embolization, recurrence rate, time from operation to reexamination among four groups (all P>0.05). CONCLUSION: The endovascular treatment maybe an ideal management for ruptured ACoAC aneurysms.

[Hydrochemical Characteristics and Influencing Factors in Different Geological Background: A Case Study in Darongjiang and Lingqu Basin, Guangxi, China].

The observation and sampling were carried out in May 2013 to April 2014 in a hydrological year for two river basins with different geological background in upstream of Li river basin. The seasonal variations of river water chemistry and its main influencing factors were discussed in this paper. The results showed that the hydrochemistry types of both Darongjiang basin with 9% of carbonates and Lingqu basin with nearly 50% of carbonates in area belonged to Ca-HCO3 type. Ca2+ and HCO3- were the main cations and anions. The main ion concentrations were higher in winter and lower in summer, affected by the change of the flow. Ca2+, Mg2+, HCO3- were mainly sourced from the weathering of carbonates by carbonic acid. The weathering of carbonates by sulfuric acid and the weathering of silicate rocks also had contribution to the river water chemistry. In addition, comparing to the Lingqu basin, the contribution of the weathering of carbonates was much more than the percent of carbonates area, because the carbonate rocks were eroded by the allogenic water. On the other hand, K+, Na+, Cl-, NO3-, SO4(2-) were mainly affected by the atmospheric precipitation and human activities. Comparing to the Darongjiang Basin, the effects of human activities on the changes of K+, Na+, Cl-, NO3-, SO4(2-) were more significant in Lingqu Basin.

[Chemical Characteristics and Source of Acid Precipitation in Guilin].

A total of 396 rainwater samples of Guilin from 2008 to 2011 were collected and analyzed for pH, 44 of which were analyzed for major ions. The analysis of pH values showed the obvious seasonal variation of acid rain in Guilin. The pollution level of summer was lower than those in other seasons, while the pollution levels in winter and spring were the highest. The investigation of fractional acidity(AF) and neutralization factors(NF) indicated that low acid rain pollution level in 2008 was caused by alkali neutralization, especially NH4+ and Ca2+. Studies of the origins of major ions showed that CI- and Na+ were mainly from sea, Ca2+ was mainly from the crustal dust while K+, SO42- and NO3- were mainly originated from anthropogenic source. Finally, the effect of regional transportation on acid rain of Guilin was analyzed and 3 originatons of acid-causing substance were oriented by an air trajectory clustering methodology based on hysplit-4 and a clustering algorithm including 1Jiangxi, Anhui, Hunan and Hubei, with high population densities, these regions contributed 19% air mass in spring, 26% in summer, 19% in autumn and 36% in winter due to the northeast wind; 2Pearl River Delta, with airflow from west Pacific passing before arriving Guilin, contributing 19% in spring, 33% in autumn and 36% in winter; 3Nanning, Liuzhou. All strong acid rain vapor air mass converged in southwest Guilin in spring, and arrived in Guilin passing Naning and Liuzhou. In summer, under the direct control of southwest monsoon, the vapor from Indian Ocean directly arrived in Guilin, accounting for 75%. The southwest airflow passing these cities accounted for 14% in autumn and 63% in winter.

[Variations of Inorganic Carbon and its Impact Factors in Surface-Layer Waters in a Groundwater-Fed Reservoir in Karst Area, SW China].

In order to understand the inorganic carbon cycle of the groundwater-fed reservoir in karst area, Dalongdong Reservoir, which is located at Shanglin County, Guangxi Zhuang Autonomous Region, China, was investigated from 12th to 20th July, 2014. Concentration of dissolved inorganic carbon (DIC), delta13C of DIC (delta13C(DIC)), partial CO2 pressure (pCO2) and CO2 flux across water-air interface were studied by observation in situ and high-resolution diel monitoring. Results show that: (1) DIC concentration and water pCO2 increased from upstream area to downstream area [DIC(average)): from 122.88 to 172.02 mg x L(-1), pCO2(average) : from 637.91 x 10(-6) to 1399.97 x 10(-6)], while delta13C(DIC) decreased from upstream area to downstream area [delta13C(DIC(average): from -4.34% per hundred to -6.97% per hundred] in the reservoir. (2) CO2 efflux across water-air interface varied from 7.11 to 335.54 mg x (m2 x h)(-1) with mean of 125.03 mg x (m2 x h)(-1) in Dalongdong reservoir surface-layer waters, which was the source of atmospheric CO2. CO2 effluxes across water-air interface in upstream area [mean 131.73 mg x (m2 x h)(-1)] and downstream area [mean 170.25 mg x (m2 x h)(-1)] were higher than that in middle area [mean 116.05 mg x (m2 x h))(-1)] in the reservoir. (3) Water pCO2 and CO2 efflux across water-air interface showed similar characteristics of diel variations, which decreased in daylight and increased in night and showed a negative correlation with chlorophyll a (Chla). Possible reasons of research results are found as follows: (1) DIC concentration, water pCO2 and delta13C(DIC) are influenced by biomass of phytoplankton, turbidity, conductivity, the depth of water and transparency, while CO2 efflux across water-air interface is controlled by both of biomass of phytoplankton and wind speed. (2) Photosynthesis, respiration and vertical motion of phytoplankton possibly affect diel variations of DIC cycle in the groundwater-fed reservoir in karst area.

[Hydrochemical Characteristics and the Dissolved Inorganic Carbon Flux in Liuzhou Section of Liujiang Basin].

An important aspect of the current global change research is using river chemical composition to reveal the chemical weathering process and its effect of carbon sink. In this study, water samples were collected and analyzed 2 ~3 times per month from January to December in 2013. The hydrochemistry belonged to HCO3-Ca type. Ca+ and HCO3- were the main cation and anion, which reflected that the hydrochemical characteristics of river were mainly affected by the dissolution of carbonate rock. The concentration of main ions varied with the seasons, which reflected that the crest value occurred in winter, followed by those in autumn and spring, and the lowest value was observed in summer. Due to the interaction of effect of dilution and effect of C2, the seasonal variation of Ca2+ and HCO3- showed that the highest value was in autumn and the lowest value was in summer. The seasonal variation law of other ions should be attributed to the effect of dilution or agricultural activities or combined action of them. Both carbonic acid and sulfuric acid took part in the chemical weathering of carbonate rocks as evidenced by stoichiometric analysis. Besides, the δ34S of sulfate ion of the river waters (δ34S: from 7. 65 per thousand to 8. 55 per thousand) showed that SO2- was originated mainly from oxidation of sulfide minerals in ore deposits and acid rain. Chemical mass balance method was applied to estimate the proportion of HCO- coming from carbonate weathering by sulfuric acid. The result was 28. 26% . On this basis, the total carbon flux of carbon ( by CO2 calculation) in Liuzhou section calculated month by month was about 8. 95 x 10(5) t . a-1. What's more, the carbon flux showed a positive correlation with flow, which implied that the discharge of catchment was the main influencing factor of carbon flux rather than the HCO3- concentration.

[Effect of hydrochemistry characteristics under impact of human activity: a case study in the upper reaches of the Xijiang River basin].

In this paper, observation and sampling were taken three times a month in a hydrological year for three typical sections of the middle and upper reaches of the Xijiang River basin, based on the data of hydrochemistry and flow, the article mainly discusses the evolution process of hydrochemistry in river under natural process and impact of human activity. Hydrochemical characteristics of 116. samples were analyzed in the study area. The hydrochemistry type in the middle and upper reaches of the Xijiang River basin belonged to HCO3- -Ca2+ type, and the chemical weathering type mainly came from carbonate rock weathering. Ca2+ and HCO3- were the main cations and anions, which reflected that hydrochemical characteristics of river in karst area mainly affected by the dissolution of carbonate rock. Na, Mg2, Ca2+ and Cl- mainly affected by natural conditions, the impact of human activity was little. K+, NO3-, SO4(2-) and HCO3- were affected by human activity in different degrees, and it showed different influence ways. This study had an important significance for the change of river hydrochemistry, water quality characteristics, and the effect on substance transported fluxes in the downstream of Pearl River and water quality protection in South China Monsoon Area.

[Summer Greenhouse Gases Exchange Flux Across Water-air Interface in Three Water Reservoirs Located in Different Geologic Setting in Guangxi, China].

Due to special hydrogeochemical characteristics of calcium-rich, alkaline and DIC-rich ( dissolved inorganic carbon) environment controlled by the weathering products from carbonate rock, the exchange characteristics, processes and controlling factors of greenhouse gas (CO2 and CH4) across water-air interface in karst water reservoir show obvious differences from those of non-karst water reservoir. Three water reservoirs (Dalongdong reservoir-karst reservoir, Wulixia reservoir--semi karst reservoir, Si'anjiang reservoir-non-karst reservoir) located in different geologic setting in Guangxi Zhuang Autonomous Region, China were chosen to reveal characteristics and controlling factors of greenhouse gas exchange flux across water-air interface. Two common approaches, floating chamber (FC) and thin boundary layer models (TBL), were employed to research and contrast greenhouse gas exchange flux across water-air interface from three reservoirs. The results showed that: (1) surface-layer water in reservoir area and discharging water under dam in Dalongdong water reservoir were the source of atmospheric CO2 and CH4. Surface-layer water in reservoir area in Wulixia water reservoir was the sink of atmospheric CO2 and the source of atmospheric CH4, while discharging water under dam was the source of atmospheric CO2 and CH4. Surface-layer water in Si'anjiang water reservoir was the sink of atmospheric CO2 and source of atmospheric CH4. (2) CO2 and CH4 effluxes in discharging water under dam were much more than those in surface-layer water in reservoir area regardless of karst reservoir or non karst reservoir. Accordingly, more attention should be paid to the CO2 and CH4 emission from discharging water under dam. (3) In the absence of submerged soil organic matters and plants, the difference of CH4 effluxes between karst groundwater-fed reservoir ( Dalongdong water reservoir) and non-karst area ( Wulixia water reservoir and Si'anjiang water reservoir) was less. However, CO2 efflux in karst groundwater-fed reservoir was much higher than that of reservoir in non-karst area due to groundwater of DIC-rich input from karst aquifer and thermal stratification.