Search

To study the recharge source, hydrochemical characteristics, and evolution process of karst underground water and surface water in the Xianghualing Mining area, we collected 32 groups of samples from karst underground water and surface water sources in and around the mining area. Based on multivariate statistical analysis, the Piper three-line diagram, Gibbs diagram, and ion ratio coefficient, this study analyzed the hydrogeochemical characteristics of karst underground water and surface water in the Xianghualing Mining area. The study systematically revealed the recharge source, recharge age, and hydrochemical evolution law of both water sources. The results showed that the karst underground water and surface water in the Xianghualing Mining area were weakly alkaline, with the main anions being HCO 3 - and the main cations being Ca 2+ . The hydrochemical types mainly included HCO 3 -Ca, HCO 3 -Ca·Mg, and HCO 3 ·SO 4 -Ca·Mg types. Atmospheric precipitation was the primary source of recharge for karst underground water and surface water, and it was also influenced by evaporation during the runoff process. However, the evaporation effect of karst groundwater was relatively small, which was closely related to modern hydrology, and the cycle replacement process was more rapid. The hydrochemical evolution characteristics of karst underground water and surface water were mainly affected by rock weathering, cation exchange adsorption, mineral dissolution, and human activities （such as agricultural and mining activities）. Ca 2+ , Mg 2+ , and HCO 3 - were primarily derived from the dissolution of carbonate minerals, with a small portion also originating from the weathering and dissolution of silicate minerals. Na + and Cl - were primarily derived from the dissolution of rock salts. Among them, Cl - , NO 3 - , and SO 4 2- were greatly affected by external inputs from agricultural activities, domestic sewage discharge, and mining activities. The research results are of great significance to the cyclical evolution process of karst underground water and surface water, as well as the protection and utilization of water resources in the Xianghualing Mining area.

Water quality is one of the most important environmental issues in the sustainable development of karst areas. To investigate heavy metal pollution and assess health risk in karst water basins around mines, 18 groups of water samples were collected from the river and groundwater in the Sidi River karst basin, and the concentrations of nine types of heavy metals(Cu, Pb, Zn, Cd, Mn, Fe, As, Cr, and Sr) were determined. Sample data were analyzed using principal component analysis, correlation analysis, water quality index, the Nemerow comprehensive pollution index, hazard quotient, and hazard index. The results showed that the Sidi River was slightly alkaline. The farther the river water samples were from the tailings reservoir, the lower were the concentrations of Cu, Pb, Zn, Cd, Mn, Fe, As, and Sr in the river water. Principal component and correlation analyses showed that heavy metals in the Sidi River karst basin mainly came from mine discharge(55.42%), carbonate weathering dissolution(21.41%), and human activities(14.72%). Eighty-two percent of the samples in the river and all the samples in the groundwater were excellent water. The Nemerow comprehensive pollution index in the river was 4.12 with strong pollution. All the hazard indices were below 1, and Pb, Zn, As, Cd, and Cr were potentially threatening metals in the Sidi River karst basin. The concentration of heavy metals changed significantly after entering the karst conduit, indicating that the unique properties of the karst aquifer affected the spatial variation of the heavy metal concentration. The results of this study can provide data reference for water resource prevention and human health protection in the Sidi River karst basin and similar karst basins.

To investigate the environmental quality and human health risks of different types of groundwater at Xiangshui, Chongzuo, several regular water quality indexes and concentrations of metals in 60 groundwater samples were measured and analyzed. The environmental quality of groundwater was analyzed by means of the Nemerow index. The health risks were assessed by using a human health risk assessment model. The regular water quality indexes and concentrations of metals of the well water, spring water, and underground river water exceeded the standards to different degrees. The environmental quality of groundwater was at a poor grade. The comprehensive evaluation score of underground river water ( F =4.26) was the lowest. The well water had the same score as spring water ( F =7.10). The high hardness and salinity were conducive to enrichment of Cr, and the reducing environment was of great advantage for the enrichment of As. The environmental geochemistry of Zn, Pb, Cd, and Cu was similar. The sources of Fe, Al, and Mn were similar. The results of the health risk assessment indicated that the health risks of well water, spring water, and underground river water were relatively high. The health risks decreased in the order of well water > underground river water > spring water. The health risks mainly came from the carcinogenic metallic element Cr. Carcinogenic risks were 4-6 orders of magnitude higher than non-carcinogenic risks. Carcinogenic risks were higher than the maximum allowance levels (5.0×10 -5 a -1 ). Non-carcinogenic risks were lower than the allowance levels (10 -6 a -1 ). Children had greater health risks than adults. The health risks of metals through the drinking pathway were 2-3 orders of magnitude higher than the values caused by the dermal contact pathway. For the sake of drinking water safety, the well water, underground river water, and spring water should be properly treated and the concentration of Cr in groundwater should be controlled before drinking.

To investigate the major ionic characteristics, seasonal variation, and controlling factors of karst groundwater at Xiangshui, Chongzuo, 210 groundwater samples were collected and measured in wet season, dry season, and flat season in 2016. The controlling factors of karst groundwater were analyzed by using multivariate statistical analysis method. The results showed that the groundwater samples were weakly alkaline fresh water and rich in Ca 2+ and HCO 3 - , which accounted for more than 75% and 70% of total ion concentration. The average concentrations of K + , Na + , Cl - , and NO 3 - decreased in the order of wet season > flat season > dry season. None of the concentrations of Ca 2+ , Mg 2+ , HCO 3 - , SO 4 2- , pH, TDS, TZ + , and TZ - showed significant seasonal variation. The hydrochemical characteristics were found to be of HCO 3 -Ca type and mainly determined by carbonate rock dissolution. Only a small proportion of them were of HCO 3 ·Cl-Ca and HCO 3 ·SO 4 -Ca type in wet season and flat season, Cl·NO 3 -Ca type appeared in flat season, and HCO 3 -Ca·Mg type appeared in dry season, reflecting the influence of dolomite and ferric mudstone dissolution in the stratum, and of NO 3 - and Cl - input from anthropogenic activities. Groundwater Ca 2+ and HCO 3 - mainly came from limestone dissolution; Na + , Cl - , K + , and NO 3 - came from atmospheric precipitation and human activities; while Mg 2+ and SO 4 2- came from dolomite and ferric mudstone dissolution. The chemical composition of groundwater was controlled by water-rock interaction, the groundwater in the carbonate aquifer was controlled by carbonate rocks dissolution, and the groundwater in villages and densely populated areas was affected by atmospheric precipitation and human activity.

The Wujing River, the largest river in Guizhou Province, is one of the most important water resources for social and economical development. Recently, with the fast population proliferation and rapid economic growth, the drainage basin is intensively interfered by anthropogenic activities. The hydrochemistry of surface water was analyzed from the upper-middle reaches of Wujiang River for investigating the hydrochemical characteristics and their main influencing factors. The results showed that the major cations of the four rivers were Ca²⁺ and Mg²⁺, accounting for more than 70%, and the main anions were HCO₃⁻ and SO₄²⁻, occupying more than 85%. The hydrochemical characteristics in the four rivers were found to be of HCO₃-Ca type, and mainly determined by the carbonate rock dissolution, while only a small proportion of them were of HCO₃ · SO₄-Ca type, reflecting the influence of SO₄²⁻ from anthropogenic activities. Compared to hydrochemical data in 1999, there was an obvious increase in cations and anions concentrations, majorly in NO₃⁻, SO2- ion concentrations, which were significantly affected by human activities. The Na⁺, K⁺ , Cl⁻ in the river mainly came from atmospheric precipitation, and Ca²⁺, HCO₃⁻, Mg²⁺, mainly came from carbonate rocks dissolution, while NO₃⁻ and SO₄²⁻ mainly came from human activities. According to principal component analysis and correlation analysis, hydrochemical composition of Liuchong River was affected by human activity, and that in the upstream of Sancha River was controlled by atmospheric precipitation and the dissolution of carbonate rocks, that to the downstream was enhanced by human activities. The main ion of Maotiao River was controlled by atmospheric precipitation and carbonate rocks dissolution, and also affected by human activity. The Nanming River, the Qingshui river's tributary, was mainly affected by human activity, while the middle and lower reaches of Qingshui River were affected by both the atmospheric precipitation and human activity.

Groundwater and surface water from the Upper and Middle Reaches of the Wujiang River were sampled and analyzed for the hydrochemistry and Carbon isotope in DIC. Then hydrochemical characteristics and the main influencing factors were investigated, and the contributions of carbonate dissolution by sulphuric acid to total(Ca2+ + Mg2+) and HCO3 were calculated using the stoichiometry method. The results showed that the advantage cations of groundwater and surface water is Ca2+, which accounted for more than 50% and the advantage anions is HCO3- and SO(4)2-, which accounted for more than 85%. The hydrochemical characteristics of most samples were of Ca-HCO3 type, and a small part of HCO3.SO4-Ca, reflecting a few samples affected by SO(4)2- from human source. The δ13CDIC of groundwater and surface water, varying from -12. 98%o to -6. 36%o with a changeable molar ratio between (Ca2+ + Mg2+) and HCO3- of 1. 11 to 1. 90, indicated that sulfuric acid has an important influence on hydrochemistry and δ3CDIC. The contributions of carbonate dissolution by sulphuric acid to total (Ca2+ + Mg2+) and HCO3 in groundwater ranged from 20. 59% to 92. 87% (average 51. 50%), and from 11. 47% to 86. 69% (average 36. 90%). While the contributions of carbonate dissolution by sulphuric acid to total (Ca2+ + Mg2+) and HCO3- in surface water ranged from 56. 14% to 94. 55% (with an average of 76. 89%), and 39. 02% to 89. 66% (with an average of 64.24%), respectively, demonstrated that sulphuric acid is an important agent of carbon rock weathering. The results of this study have a great significance for the protection and development and utilization of water resources in the Wujiang River basin and for karst carbon cycle research.

The riverine carbon flux is a critical component of global carbon cycle. Riverine water samples were collected from eleven hydrometric stations in the main stream of Pearl River and its tributaries during April and July, 2012. The samples were analyzed for the space and seasonal distribution characteristics of the riverine suspended substance and carbon compositions. Carbon fluxes and erosion modulus of Pearl River basin were also estimated in Boluo, Shijiao, Gaoyao, namely Dongjiang, Beijiang, Xijiang, in these two hydrological seasons. The results showed that the total suspended substance (TSS) and organic carbon, including total particulate organic carbon (POC) and dissolved organic carbon (DOC) have higher concentration in the high-water season than that in the normal-water season. Dissolved inorganic carbon (DIC) has an overwhelming concentration compared to other carbon compositions in Pearl River basin. The DIC concentration shows an order of Xijiang, Beijiang and Dongjiang from high to low. The percentage of allogenic POC in Xijiang, Beijiang and Dongjiang are 78%, 72%, 26%, respectively, and C3 plants are the main sources of allogenic POC in those three tributaries. The transported fluxes of TSS, total carbon (TC), POC, particulate inorganic carbon (PIC), DOC, DIC, total particulate carbon (TPC) and total organic carbon (TOC) are 134 x 10(12),12.69 x 10(12), 2.50 x 10(12), 1.01 x 10(12), 1.13 x 10(12), 8.05 x 10(12), 3.51 x 10(12) and 3.65 x 10(12) g x a(-1), respectively, and the erosion modulus of those compositions are 309 x 10(6), 28.98 x 10(6), 5.75 x 10(6), 2.27 x 10(6), 2.56 x 10(6), 18.4 x 10(6), 8.02 x 10(6) and 8.31 x 10(6) g x (km2 x a)(-1), respectively. Compared with average values of global large rivers, the erosion modulus of DOC, POC, and TOC in Pearl River basin are higher than the corresponding values.