[Controlling Factors of Groundwater Salinization and Pollution in the Oasis Zone of the Cherchen River Basin of Xinjiang]

Groundwater is a vital resource for local human life and production in the oasis zone of the Cherchen River Basin of Xinjiang. Understanding the controlling factors of groundwater salinization and pollution is of great significance for the sustainable utilization of groundwater resources and protection of the ecological environment in desert oasis areas. In light of this, a total of 36 single structure unconfined groundwater samples and 54 multi-layered structure unconfined and confined groundwater samples were collected from the oasis zone of the Cherchen River Basin and evaluated for the distribution characteristics and pollution status of major ions. Hydrogeochemical methods (e.g., Piper diagram, multivariate statistics, Gibbs model, and relationships among ions) were used to determine the main controlling factors of groundwater salinization and pollution. Differences in hydrogeochemical zonation were found from the single structure unconfined aquifers in sloping plains of piedmont areas to the multi-layered structure unconfined and confined aquifers in alluvial-proluvial plain areas, and Cl-Na (87.8%) was the main hydrochemical type in the groundwater of the study area. The quality of single structure unconfined groundwater was starkly better than that of the multi-layered unconfined and confined groundwater, which was mainly caused by Na+ (mean value of 9 969 mg·L-1), Cl- (13 687 mg·L-1), and SO42- (5 840 mg·L-1). Moreover, the natural hydrogeochemical process was the main reason for the deterioration of groundwater quality. The hydrochemistry was mainly controlled by the water-rock interaction and evaporation processes. The mineral dissolution of silicates and evaporites was an important source of chemical ions in the groundwater. Furthermore, the chemical weathering of evaporites combined with the processes of evaporation and cation exchange had a significant influence on the salinization of multi-layered unconfined and confined groundwater in alluvial-proluvial plain areas. In addition, synthetic fertilizers were the main pollution sources of NO3- in groundwater in the intensive agricultural zones.

[Hydrochemical Characteristics and Control Factors of Surface Water and Groundwater in Huainan Coal Mine Area]

To clarify the hydrochemical characteristics and control factors of surface and underground water in Huainan mining area, 115 groups of groundwater and 30 groups of surface water samples were collected, and the hydrogeochemical characteristics of surface water and groundwater in Huainan mining area were analyzed. Additionally, the hydrochemistry evolution law was discussed by comprehensively using mathematical statistics, the Piper triangular diagram, Gibbs diagram, mineral stability field diagram, and ion ratio relationship, etc. The results showed that the groundwater and surface water in the study area were weakly alkaline, the dominant anion was HCO3-, and the dominant cations were Ca+ and Na+. The hydrochemical types of groundwater and surface water were dominated by HCO3-Ca type and HCO3-Ca·Na·Mg type, respectively. The hydrochemical composition of groundwater and surface water was mainly controlled by rock weathering, as well as by alternating adsorption of cations and evaporation concentration. Silicate and carbonate minerals were mainly dissolved in the water-rock interaction. The main ions such as Ca2+, Mg2+, and HCO3- came from the dissolution of carbonate rocks. The Cl-, SO42-, NO3-, and Ca2+ were affected by exogenous inputs caused by human activities. The chemical components of groundwater and surface water in Huainan coal mining area were affected by water-rock interactions and human activities, and groundwater was greatly affected by human activities.

Identification of Gas Channeling and Construction of a Gel-Enhanced Foam Plugging System for Oxygen-Reduced Air Flooding in the Changqing Oilfield

The accurate identification of gas channeling channels during foam-assisted oxygen-reduced air flooding (FAORAF) and the analysis of the main controlling factors are essential to propose reasonable and effective countermeasures to enhance oil recovery (EOR). However, there are few comprehensive studies on identifying gas channeling channels, the influencing factors, and the corresponding plugging EOR systems in FAORAF. The channeling channels of the injection and production wells of the Changqing Oilfield, China, under varying development schemes are identified utilizing fuzzy membership function theory in this work to obtain their primary distribution. The characteristics and influence factors of gas channeling channels are analyzed by numerical simulation using CMG. The recovery performance of each foam blocking system is evaluated by twin-tube sand pack models. As well, based on the features of reservoir fractures, a new gel-enhanced foam plugging system is developed. The results show that channeling channels chiefly develop along NE 60–70° and that foam could reduce gas channeling. Natural and artificial fractures are the principal factors causing gas channeling, followed by the injection method and gas injection rate. Under the premise of the injection and migration efficiency, the optimal gel system is a 0.1% HPAM + 0.1% organic chromium crosslinking agent. The addition of gel increases the viscosity of the liquid phase and strengthens the mechanical strength of the foam liquid film. At a permeability ratio of 12, the recovery factors of the binary plugging systems composed of microspheres, PEG, and gel combined with foam are 40.89%, 45.85%, and 53.33%, respectively. The movable gel foam system has a short breaking time (only 18 days) and a recovery factor of about 40% at a permeability ratio of 20. To be suitable for oil reservoirs with microfractures, an improved ternary gel foam system—0.1% HPAM + 0.1% chromium crosslinking agent + 0.05–0.1% nano-SiO₂—is developed. Compared with the binary gel foam system, the recovery rate of the new nano-SiO₂ gel foam system after 15 days of ageing using the core splitting test is 25.24% during the FAORAF process, increasing by 12.38%.

[Spatial Characterization of Stable Isotope Composition of Organic Carbon from Farmland Soils in Chongqing]

Soil was sampled from 182 profiles in typical farmlands of Chongqing and analyzed for the stable carbon isotope composition of organic matter (δ¹³C_SOC). The results showed that the values of δ¹³C_SOC for each soil profile were gradually increasing with increasing soil depth, and the mean values were (-23.63±1.53)‰, (-22.43±1.59)‰, and (-21.42±1.90)‰ for surface, middle, and bottom layers, respectively. The δ¹³C_SOC values in the northeastern region of Chongqing tended to be more negative, whereas those in central Chongqing were less negative. Paddy fields showed the most negative values of δ¹³C_SOC, followed by rice-upland rotating fields and upland fields, with the average being (-25.32±0.93)‰, (-23.17±1.37)‰, and (-24.75±1.28)‰ for the surface layers, respectively. For different soil types, the δ¹³C values in the surface layers were in the order of paddy soil<alluvial soil<purplish soil<calcareous soil<yellow soil. According to the regression-tree analysis, the crop types predominantly influenced the variation in δ¹³C_SOC in surface soils, and soil types mainly affected that in the middle- and bottom-layer soils. Other factors, such as soil properties (TN, SOC, and pH) and meteorological conditions (precipitation and air temperature) played only minor roles in the variation of δ¹³C_SOC. In short, the stable isotope composition of organic carbon in the surface soils was primarily controlled by the input carbon source, whereas that in the deeper layers was closely linked with carbon cycling processes within the soils.

Distribution Characteristics and Controlling Factors of Soil Total Nitrogen: Phosphorus Ratio Across the Northeast Tibetan Plateau Shrublands

Nitrogen (N) and phosphorus (P) stoichiometry have significant effects on nutrient cycles in terrestrial ecosystems. However, our understanding of the patterns and the driving factors of soil N:P ratios in the Tibetan Plateau shrublands remains limited. Our study aimed to quantify the distribution of soil N:P ratio and its controlling factors based on soil, plant, and climate factors from 59 sites in shrublands across the northeast Tibetan Plateau. The kriging interpolation method was used to quantify the soil N:P distribution. Spatially, the soil N:P ratio was higher in the south than in the north and lower in the west than in the east. The soil N:P ratio in the northeast Tibetan Plateau shrublands was mainly explained by edaphic factors, which also played an important role in regulating the effects of plant and climate factors on soil N:P ratios. Mean annual precipitation, instead of mean annual temperature, significantly controlled the soil N:P ratios, and its effect on the pattern of soil N:P ratios differed between alpine shrublands and desert shrublands. The N:P ratios of different organs in shrublands also played different roles in shaping the soil N:P ratios in alpine and desert shrublands. These results provide support for the hypothesis that edaphic factors were the dominant drivers of spatial variation in soil N:P ratios across the northeast Tibetan Plateau shrublands, and our study contributes to a deeper understanding of biogeochemical cycling at high altitudes.

[Sources Identification, Ecological Risk Assessment, and Controlling Factors of Potentially Toxic Elements in Typical Lead-Zinc Mine Area, Guizhou Province, Southwest China]

Carbonatite and basalt are widely distributed in southwest China, and potentially toxic elements (PTEs) are associated with the naturally high background properties. It is important to carry out ecological risk assessments and identify potential sources of PTEs. A total of 3180 soil samples (0-20 cm) were collected in Hezhang county, a typical high background area of PTEs with the parent lithology of carbonatite and basalt. Samples were obtained from 18 large lead-zinc mines, which belong to a multi-ecological risk superimposed area with high ecological risk. The concentration of PTEs (Cd, Cr, As, Hg, Pb, Cu, Zn, and Ni) in the topsoil were analyzed, and statistical analysis (SA), geographic information system (GIS), enrichment factor (EF), potential ecological risk index (RI), and positive matrix factorization (PMF) methods were used to assess the ecological risk and quantify sources of PTEs. The mean values of PTEs concentrations in topsoil were 24.55, 2.25, 176.40, 89.60, 0.19, 64.20, 102.00, and 257.00 mg·kg^-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than the average background value (ABV) of soils in Guizhou Province. The average concentrations of Cd, Cr, Cu, Ni, Pb, and Zn exceeded the screening values specified for the soil contamination risk in agricultural land (GB 15618-2018) by 7.50, 1.18, 1.79, 1.07, 1.40, and 1.29 times, respectively. The EF showed that Cd had a large area of moderate pollution; Pb, Zn, and Cu had a small area of slight pollution; the EFs values of Hg, Cr, Ni, and As were near the baseline value (EF≈1), and contaminations were slight or nonexistent. The PMF indicated that there were five sources, namely pyrite mines, lead-zinc mines, natural sources of basalt and carbonatite, and agricultural activities; the risk contribution ratios were 5.25%, 27.37%, 28.94%, 17.91%, and 20.53%, respectively. The most toxic coefficients of Hg and Cd were mainly natural sources, with contribution ratios of 86.3% and 72.7%, respectively. The soil samples in the mining areas expectedly contained high ratios of Zn/Cd and Pb/Cd, which confirmed that PTEs in the soil were mainly derived from the smelting wastes. The contents of metal oxides such as Fe, Mn, and Si were the influencing factors of PTEs enrichment. On the contrary, soil samples exhibited much lower Zn/Cd and Pb/Cd ratios in non-mining areas, indicating that the main origin of these metals in soil was the smelting flue gas dusts and geological background.

[Provenance of Groundwater Solute and Its Controlling Factors in Yancheng Area]

Affected by human activities and climate change, the deterioration of groundwater quality could continue to intensify, and it is difficult to repair after being polluted. In order to reduce the vulnerability of groundwater safety, it is urgent to strengthen research on groundwater quality. To analyze the characteristics of hydrochemical composition and control factors and to explore the impact of human activities, groundwater sampling was conducted in the alluvial and marine plains of Yancheng area, where industrial and agricultural activities were intense. The results showed that:① the TDS value of shallow groundwater was between 211 and 3790 mg·L^-1, of which, brackish water samples accounted for 30.28% in Yancheng. The order of the concentration of anions and cations was:HCO₃^->Cl^->SO₄^2->NO₃^- and Na⁺>Ca²⁺>Mg²⁺>K⁺. However, from Type Ⅰ/Ⅱ water to Type Ⅴ water, with the increase in TDS value, the dominant anions and cations evolved from HCO₃ type to Cl/SO₄ type and from Ca type to Na type, respectively. ② In the initial Type Ⅰ/Ⅱ water bodies, Na⁺ should have mainly originated from the weathering erosion of albite, whereas Ca²⁺, Mg²⁺, and HCO₃^- should have had a common rock weathering source. In the subsequent water quality evolution process, the factors that led the TDS value to increase, or even to exceed the standard, were not limited to rock weathering, and the effects of evaporation-concentration and ion exchange were also very worthy of attention. ③ The enrichment factor analysis showed that the Cl^- and SO₄^2- were mainly from the input of sea salt sources, and their proportions were gradually increasing from the freshwater areas of Type Ⅰ/Ⅱ in the west to the brackish water areas in the east. However, Ca²⁺, K⁺, and HCO₃^- were mainly derived from crustal sources, and Ca²⁺ was precipitated due to saturation. ④ The NO₃^- derived from agricultural fertilizers was limited to water of category Ⅰ/Ⅱ and Ⅲ-1 (500 mg·L^-1 < TDS ≤ 750 mg·L^-1). Discharge of urban sewage mainly affected Type Ⅲ water bodies. The nitrates formed by agricultural organic fertilizers were mainly distributed in the water of Type Ⅳ and Ⅴ, which was the main rice-producing area of Sheyang, Jiangsu, and the SO₄^2- formed by human activities in this area could be ignored. These should be one of the achievements in the development of regional ecological agriculture.

[Hydrochemical Characteristics and Controlling Factors of Groundwater in the Leizhou Peninsula]

Groundwater resources in the Leizhou Peninsula provide a strong support for the economic and social development. Therefore, understanding the chemical characteristics and formation mechanism of groundwater in this area is necessary for the rational exploitation and sustainable utilization of water resources. In this study, 43 groundwater samples were collected, and the hydrochemical characteristics and controlling factors were analyzed by descriptive statistical analysis, Piper triangular diagrams, ArcGIS spatial interpolation, Gibbs diagram, and ion ratios. The results showed that:① The anions and cations of the groundwater in the study area were mainly HCO₃^-, Ca²⁺, and Na⁺, and the hydrochemical types were mainly HCO₃-Cl-Na-Ca, HCO₃-Cl-Na-Ca-Mg, HCO₃-Cl-Na-Mg, and HCO₃-Na. The contents of Cl^-, SO₄^2-, and Na⁺were higher in the west of Leizhou City compared to other areas. The sites with higher contents of HCO₃^-, NO₃^-, Ca²⁺, Mg²⁺, and K⁺ were mainly concentrated in the southwest and eastern coastal areas. ② The chemical evolution of groundwater was mainly affected by water-rock interaction, cation alternating adsorption, and anthropogenic activities. The sources of Na⁺ and K⁺ were mainly from evaporative and silicate rocks, Ca²⁺ and Mg²⁺ were mainly from carbonate karstification, while NO₃^- originated from anthropogenic activities.

[Spatial Hydrochemical Characteristics and Controlling Factors of Surface Water in the Yancheng Area]

Surface water resources are crucial to economic development in China's eastern coastal areas. Under the influence of intense human activities, problems such as abnormal water quality and pollution are very prominent. Here, the chemical composition of surface waters and their controlling factors were analyzed in the Yancheng area. The results showed that:① The surface water pH is low and the concentrations of total dissolved solids(TDS) are high in the study area. pH is likely controlled by the acidic organic pollutants discharged by human activities as well as acidic substances formed by anaerobic decomposition in soils. TDS data showed low values in the west and high values in the east, and low values in north and high south of the study region. ② Cation content was dominated by Na⁺, anions were dominated by HCO₃^- and Cl^-, and, overall, hydrochemical composition was controlled by HCO₃-(Ca+Na), although there was significant variability between the different regions. ③ Because the silt layer in the region is mainly composed of clay, subclay, and sandstone, the soluble matter in surface water is mainly derived from the decomposition of Na-feldspar in silicate debris via carbonation, supplemented by carbonation. Due to the low-lying terrain and high groundwater level in the tidal flat area, solutes are significantly affected by evaporation-driven concentration alongside evaporite weathering replenishment. ④ Although the surface waters in different regions were found to be affected by human activities to varying degrees, the impact was always strong. In particular, in areas of tidal wetland expansion, water quality is not only affected by urban sewage and agricultural irrigation but also industrial wastewater discharge.

Assessment of the Evolution of Groundwater Chemistry and Its Controlling Factors in the Huangshui River Basin of Northwestern China, Using Hydrochemistry and Multivariate Statistical Techniques

Groundwater is an eco-environmental factor and critical resource required for human life and socioeconomic development. Understanding the evolution of groundwater chemistry and its controlling factors are imperative for preventing its deterioration and ensuring its sustainable use. We studied the characteristics of groundwater chemistry in the Huangshui River Basin in Qinghai Province, China using hydrochemical techniques. Additionally, we identified the controlling factors of groundwater chemistry in this region using multivariate statistical techniques. Seventeen hydrochemical parameters of groundwater were investigated at 156 sites in June 2019. The results showed that total hardness, Fe, NO₃⁻, SO₄²⁻, and Cl⁻ were primary pollution factors of groundwater in this region, and that 33.3%, 35.3%, 8.97%, 23.1%, and 7.69% of the samples exceeded Grade III standards for groundwater quality in China, respectively. Land use types also significantly affected groundwater hydrochemistry. The hydrochemical composition of groundwater in industrial areas is more strongly influenced by human activities. The major hydrochemical types identified in the region were HCO₃-Ca·Mg and HCO₃·SO₄-Ca·Mg. Additionally, high proportions of SO₄ (50.6%), Na (32.1%), and Cl (13.5%) groundwater types revealed the influence of anthropogenic activities on the groundwater hydrochemistry. Rock weathering was the major factor influencing the groundwater hydrochemistry, while evaporation–condensation and anthropogenic activities also influenced the hydrochemical characteristics of groundwater. The hydrochemical composition of groundwater was mainly controlled by silicate rock weathering. The main controlling factors of groundwater hydrochemistry were water–rock interactions, “physicochemical” factors (nature processes), domestic sewage, chemical fertilizer, and industrial sewage (human activities).

[Hydrochemical Characteristics and Analysis of the Qilihai Wetland, Tianjin]

Hydrochemistry is an important parameter for wetland water environmental assessment. To study the hydrochemistry and main ion sources in the Qilihai wetland in Tianjin, river water, groundwater, and water in the marsh were collected and analyzed. The results show that:① The river and marsh waters are SO₄·Cl-Na in type and groundwater water is HCO₃-Na and HCO₃-Na·Ca in type. The water in the marshes is mainly recharged by river water and the exchange of shallow groundwater with river water is notable; ② Precipitation has little effect on the chemical composition of the water. Na⁺ and K⁺ were derived from the dissolution of salt rock and evaporative concentration. Ca²⁺, Mg²⁺, and HCO₃^- in the river and marsh water are mainly derived from the dissolution of evaporite salt rock. Ca²⁺, Mg²⁺, and HCO₃^- in the groundwater are mainly derived from carbonate mineral dissolution; ③ The hydrochemical composition of the river water and groundwater is notably affected by ion exchange, but this was not observed in the marsh water. Furthermore, SO₄^2- and NO₃^- are affected by human activity. During the dry season, the river and marsh water are affected by evaporite salt rock dissolution, evaporation, and human effects, while in wet season, river water is mainly affected by carbonate dissolution and human activities. These observations demonstrate how that hydrochemical composition of this wetland is controlled by a combination of natural factors and human activities.

[Water Sources and Factors Controlling Hydro-chemical Compositions in the Yiluo River Basin]

An important tributary in the middle stream of the Yellow River, the Yiluo River consists of the Luohe River and Yihe River, which converge at Yanshi City. Mining activities were widely distributed in the upstream of the Yiluo River Basin (YRB), while residential areas concentrated in the downstream were coupled with extensively industrial and agricultural activities. To illustrate the influences of variable anthropogenic activities on the hydro-chemical composition of river water of the YRB, water samples from the main stream and tributaries were collected in the flood season (August) and normal season (December), respectively. The hydrogen and oxygen isotope values coupled with cation and anion content were analyzed. Temporal and spatial variations of hydrogen and oxygen isotopes and ion content were utilized to elucidate the sources and factors controlling the hydro-chemical composition of the river water, and to illustrate the pathways of human effects. The results demonstrated that:① Average hydrogen and oxygen isotope values (δD and δ¹⁸O) of Luo River water were -56‰ and -7.9‰, and -55‰ and -8.1‰ in the flood season and normal season, respectively. Mean δD and δ¹⁸O values of Yi River water were -49‰ and -6.9‰, and -53‰ and -7.8‰ in the flood season and normal season, respectively. These temporal variations indicated that river water was mainly recharged by local atmospheric precipitation. ② The dominant water hydro-chemical type was HCO₃-SO₄-Ca-Mg in the main stream of the YRB, and the ratios of Ca²⁺ and HCO₃^- molar equivalent concentrations in the flood season were lower than those in the normal season, while the ratios of SO₄^2- molar equivalent concentrations were higher than those in the normal season, indicating more sulfate dissolved in the river water in the flood season. ③ Carbonic acid and sulfuric acid simultaneously reacted with carbonate and silicate rocks, and in the Luo River more carbonate rocks were weathered, while in the Yi River more silicate rocks were weathered. ④ Human effects on river water were mainly concentrated in the upstream where wastewater input was derived from mining activities, while in the downstream pollution of the river was due to industrial wastewater and sewage input. ⑤ Spatial variations of sulfate sulfur isotope values were mostly due to differences between anthropogenic activities in the upstream and downstream of the Yiluo River. Negative sulfur isotope values in the upstream river water confirmed dissolved sulfate from sulfide mineral oxidation, which also indirectly verified the rock chemical weathering by sulfuric acid in this area. Positive sulfur isotope values in downstream river water were connected with industrial wastewater and sewage.

[Chemical Evolution of Groundwater in the Tacheng Basin of Xinjiang in the Process of Urbanization]

With the development of the local economy, the volume of groundwater production has increased continuously in the past decades in the Tacheng Basin of the Xinjiang Uygur Automous Region. Previous studies have not provided a clear pattern of the chemical composition evolution of groundwater and its driving force in this basin, which makes the future development and utilization of groundwater riskier. This study carried out systematic sampling and analysis of groundwater chemistry in this basin, and the chemical evolution of groundwater in the basin was analyzed by comparison with historical hydrochemical data. The results show that Ca²⁺ and Na⁺ are the main cations in the groundwater, HCO₃^-, SO₄^2- are the main anions in the groundwater, and freshwater is widely distributed. The chemical types of groundwater changed from HCO₃-Ca and HCO₃·SO₄-Ca·Mg in the source zone in front of the mountains to SO₄·HCO₃-Na·Ca type in the plain area. In comparison with the hydrochemical data of 1979, HCO₃ and SO₄·HCO₃ type groundwater increased significantly. SO₄ and Cl type groundwater with high total dissolved solids decreased significantly. However, the Cl^- and SO₄^2- concentration and total hardness in the groundwater around the cities and towns increased. Aquifer material and the change of flowing field are the two controlling factors of groundwater chemical change, but the leakage of waste water from city drainage channels also affects the groundwater chemistry drastically.

[Groundwater Chemistry Characteristics and the Analysis of Influence Factors in the Luochuan Loess Tablelands]

Groundwater is of great importance to the loess area, and its hydrochemical characteristics and control factors are of great significance for the utilization and management of groundwater resources. In this study, groundwater hydrochemical characteristics and their controlling factors were analyzed using descriptive statistical analysis, Piper diagrams, Gibbs diagrams, forward derivation modeling, and correlation analysis. The results show that:① Groundwater is weakly alkaline, has low salinity, and has the water chemical type Ca-Mg-HCO₃; the dominant anions and cations were HCO₃^- and Ca²⁺, which accounted for 58% to 59% of the anions and 40% to 80% of the cations, respectively; ② The ion content of the groundwater, particularly the dominant anions and cations, varied, which may have been affected by factors such as precipitation leaching of soil, cation exchange, and the horizontal flow of groundwater; ③ The main factors affecting the ion content of the groundwater are the weathering of carbonate and silicate rock, while the contribution of evaporite dissolution, human activity, and atmospheric input is very small. Carbonate weathering is a dominant source of ions in the groundwater, having an average contribution of 47%-85%, while the contribution of silicate rock weathering is between 6% and 38%. The dissolution of evaporite as a solute source was not important, contributing an average of 3%. Based on these results, it appears that the deep loess provides favorable conditions for the storage of high-quality groundwater, and the existing water quality is dominated by natural factors.

[Major Ionic Characteristics and Controlling Factors of Karst Groundwater at Xiangshui, Chongzuo]

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 Ca²⁺ and HCO₃^-, which accounted for more than 75% and 70% of total ion concentration. The average concentrations of K⁺, Na⁺, Cl^-, and NO₃^- decreased in the order of wet season > flat season > dry season. None of the concentrations of Ca²⁺, Mg²⁺, HCO₃^-, SO₄^2-, pH, TDS, TZ⁺, and TZ^- showed significant seasonal variation. The hydrochemical characteristics were found to be of HCO₃-Ca type and mainly determined by carbonate rock dissolution. Only a small proportion of them were of HCO₃·Cl-Ca and HCO₃·SO₄-Ca type in wet season and flat season, Cl·NO₃-Ca type appeared in flat season, and HCO₃-Ca·Mg type appeared in dry season, reflecting the influence of dolomite and ferric mudstone dissolution in the stratum, and of NO₃^- and Cl^- input from anthropogenic activities. Groundwater Ca²⁺ and HCO₃^- mainly came from limestone dissolution; Na⁺, Cl^-, K⁺, and NO₃^- came from atmospheric precipitation and human activities; while Mg²⁺ and SO₄^2- 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.

[Sources, Distribution of Main Controlling Factors, and Potential Ecological Risk Assessment for Heavy Metals in the Surface Sediment of Hainan Island North Bay, South China]

The distribution characteristics of the content of As, Cr, Cu, Hg, Pb, Zn, and Cd were researched based on the geochemical analysis of 159 surface sediment samples in Haikou Bay, Puqian Bay, Dongzhai Harbor, and Mulan Bay Mathematical statistics methods were used to interpret the sources of heavy metals, and the main controlling factors for heavy metal distribution were confirmed, having been analyzed qualitatively and semi-quantitatively. The results showed that the average contents of As, Cd, Cr, Cu, Hg, Pb, and Zn were 8.40, 0.06, 32.50, 8.32, 0.02, 18.77, and 35.87 μg·g^-1, respectively. High contents of Cr, Cu, Hg, Pb, and Zn are mainly distributed in estuaries and harbors. The content of As increased gradually from south to north in the research area, while Cd gathered mainly in Haikou Bay. The source of Cu, Zn, Hg, Pb, Cr, and Cd in sediment was terrestrial input, which was controlled by anthropogenic pollution and migration of weathered products from mother rock. The source of As could be overseas material input. The grain size of sediment was the main factor controlling the contents of Cu, Zn, Hg, Pb, and Cr, and it was found that sediments with a finer grain size have more heavy metals adsorbed. The high As content was controlled mainly by the natural geological background factor, while the content of Cd reflected the difference in regional pollution caused by differing development in cities. Three surface sediment samples were evaluated as class Ⅱ of the National Marine Sediment Standard due to the content of As, while six surface sediment samples were evaluated as class Ⅱ due to the content of Cr, of which the pollution degree was moderate. The concentrations of Cd, Cu, Hg, Pb, and Zn in all of the 159 sediment samples fall in the Ⅰ class, of which the pollution degree is low. The degree of pollution for seven heavy metals were arranged in the following order:As > Cr > Pb > Zn > Cu > Cd > Hg. The potential ecological risk assessment results indicated that all heavy metals in surface sediment caused low levels of pollution generally, and that each heavy metal element was at a low ecological risk level. The order for the ecological risk of the seven heavy metals was:As > Hg > Cd > Pb > Cu > Cr > Zn; therefore, As was the main ecological risk factor. In general, the potential ecological risk for heavy metals was low, which illustrated that the marine environment in the study area was excellent.

[Temporal Dynamics of Stable Isotopic Composition in Lake Taihu and Controlling Factors]

The composition of hydrogen and oxygen stable isotopes in lake water is important to the researches in hydrology, meteorology and paleoclimatology. In this study, long-term and continuous measurement on the compositions of HDO and H₂¹⁸O in lake water (δD_L and δ¹⁸O_L) was conducted over Lake Taihu, the deuterium excess (d_L) was calculated, and the temporal variability and controlling factors were analyzed. The results indicated that ① the variation of isotopic enrichment in lake water was significant, ranging from -59.8‰ to -24.2‰ for δD_L, from -8.6‰ to -2.6‰ for δ¹⁸O_L, and from -7.9‰ to 12.9‰ for d_L, respectively. In comparison to cold season, δD_L and δ¹⁸O_L were higher and d_L was lower during warm season. ② On monthly time-scale, lake evaporation and the ratio of total water inputs lost by evaporation controlled the isotopic enrichment in lake water. When lake evaporation or the ratio increased, δD_L and δ¹⁸O_L increased, but d_L decreased. ③ Over Lake Taihu, the isotopic composition in precipitation and water temperature did not control the isotopic enrichment. The results provide scientific reference for isotope hydrology and the researches related to the isotopic enrichment in lake water in meteorology and paleoclimate.

Nitrate removal, communities of denitrifiers and adverse effects in different carbon substrates for use in denitrification beds

Denitrification beds are containers filled with wood by-products that serve as a carbon and energy source to denitrifiers, which reduce nitrate (NO(3)(-)) from point source discharges into non-reactive dinitrogen (N(2)) gas. This study investigates a range of alternative carbon sources and determines rates, mechanisms and factors controlling NO(3)(-) removal, denitrifying bacterial community, and the adverse effects of these substrates. Experimental barrels (0.2 m(3)) filled with either maize cobs, wheat straw, green waste, sawdust, pine woodchips or eucalyptus woodchips were incubated at 16.8 °C or 27.1 °C (outlet temperature), and received NO(3)(-) enriched water (14.38 mg N L(-1) and 17.15 mg N L(-1)). After 2.5 years of incubation measurements were made of NO(3)(-)-N removal rates, in vitro denitrification rates (DR), factors limiting denitrification (carbon and nitrate availability, dissolved oxygen, temperature, pH, and concentrations of NO(3)(-), nitrite and ammonia), copy number of nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ) genes, and greenhouse gas production (dissolved nitrous oxide (N(2)O) and methane), and carbon (TOC) loss. Microbial denitrification was the main mechanism for NO(3)(-)-N removal. Nitrate-N removal rates ranged from 1.3 (pine woodchips) to 6.2 g N m(-3) d(-1) (maize cobs), and were predominantly limited by C availability and temperature (Q(10) = 1.2) when NO(3)(-)-N outlet concentrations remained above 1 mg L(-1). The NO(3)(-)-N removal rate did not depend directly on substrate type, but on the quantity of microbially available carbon, which differed between carbon sources. The abundance of denitrifying genes (nirS, nirK and nosZ) was similar in replicate barrels under cold incubation, but varied substantially under warm incubation, and between substrates. Warm incubation enhanced growth of nirS containing bacteria and bacteria that lacked the nosZ gene, potentially explaining the greater N(2)O emission in warmer environments. Maize cob substrate had the highest NO(3)(-)-N removal rate, but adverse effects include TOC release, dissolved N(2)O release and substantial carbon consumption by non-denitrifiers. Woodchips removed less than half of NO(3)(-) removed by maize cobs, but provided ideal conditions for denitrifying bacteria, and adverse effects were not observed. Therefore we recommend the combination of maize cobs and woodchips to enhance NO(3)(-) removal while minimizing adverse effects in denitrification beds.