[Comparison on the Hydrogeochemical Characteristics of Typical Karst Groundwater System in Southwest China, a Case of Qingmuguan and Laolongdong in Chongqing].

To study the hydrogeochemical characteristics of southwestern typical karst underground river influenced by different land-use types and human activities, underground rivers of Qingmuguan and Laolongdong, which have similar geological background in Chongqing, were contrastively analyzed from the scale of monthly and rainfall event variation. By the means of independent t-test and principal component analysis(PCA), the results showed that ions of Ca2+, HCO3-, Mg2+, K+, NO3-, Na+, SO42-, Cl- and conductivity were distinctly different at the outlet of the two observed underground rivers, Jiangjia spring and Laolongdong. Compared with Laolongdong, Jiangjia spring showed larger monthly variation range and mean concentrations of K+, NO3-, but ions of Na+, SO42-, Cl- showed an opposite trend. Water-rock interaction played an important role in the hydrogeochemical characteristics and variations of two observed karst underground rivers. Qingmuguan underground river was mainly affected by agricultural activities, while Laolongdong underground river was dominantly influenced by urban and industrial activities. Owing to the difference in manner and intensity of human activities, the two observed karst underground river systems responded differently during a single rainfall event. The variation of water chemical indicators that highly corresponded to discharge at Jiangjia spring were relatively disordered at Laolongdong. It was shown that the hydrogeochemical characteristic of Qingmuguan was primarily influenced by soil erosion and agricultural activities, followed by water-rock interaction, while the hydrochemical characteristic of Laolongdong was dominantly influenced by water-rock interaction, followed by urban activities, industrial activities and soil erosion.

[Hydrochemistry and Dissolved Inorganic Carbon Stable Isotope of Shibing Dolomite Karst Area in Guizhou Province].

Totally 49 water samples were collected in Shibing Dolomite Karst World Natural Heritage Site in Guizhou Province to analyze the characteristics and controlling factors of both the surface and underground waters, as well as the features and their origins of the dissolved inorganic carbon isotope. It was found that the pH of the study area was neutral to alkaline with low concentrations of total dissolved solids. The cations were dominated by Ca2+, Mg2 and anions by HCO3-, featured by HCO3-Ca x Mg type water. The ratios of Cl-, NO3- and SO4(2-) in the allogenic water from the shale area in the northern catchment were higher than those in autogenic water from the dolomite karst area, so did the concentration of Si. The SIc and SId of the allogenic waters in the shale area were negative. After the waters entered into and flew by the dolomite karst area, both the SIc and SId increased to over 0. It could be told by the water chemistry that the hydrochemistry was little impacted by the rainfall and human activities. The Gibbs plot revealed that the chemical composition of the waters was mainly controlled by rock weathering. The δ(13)C(DIC) of the surface waters ranged from -8.27% to -11.55% per hundred, averaging -9.45% per hundredo, while that of the underground waters ranged from -10.57% per hundred to -15.59% per hundred, averaging -12.04% per hundred, which was lighter than that of surface water. For the distribution features, it was found the δ(13)C(DIC), of the upper reaches of branches of Shangmuhe River was lighter than that of the lower reach, while that of the main river Shangmuhe River was relatively complex. Based on the mass balance of stable isotopes and the δ(13)C(DIC), the ratio of the origin of DIC of the ground water was calculated. It was found that 51.2% was from soil CO2, and 48.8% was from the rock itself.

[Impact of Rocky Desertification Treatment on Underground Water Chemistry and Dissolved Inorganic Carbon Isotope in Karst Areas].

Five springs representing different land-use types and different karst rocky desertification treatment models were chosen at the Huajiang Karst Rocky Desertification Treatment Demonstration Site in Guanling-Zhenfeng Counties in Guizhou, to analyze the features of underground water chemistry and dissolved inorganic carbon isotopes (δ13C(DIC)) and reveal the effect of rocky desertification treatment on karstification and water quality. It was found that, the underground water type of the research area was HCO3-Ca; the water quality of the springs which were relatively less affected by human activities including Shuijingwan Spring (SJW) , Gebei Spring (GB), and Maojiawan Spring (MJW) was better than those relatively more affected by human activities including Diaojing Spring (DJ) and Tanjiazhai Spring (TJZ) , the main ion concentrations and electrical conductivity of which were higher; pH, SIc and pCO2 were sensitive to land-use types and rocky desertification treatment, which could be shown by the higher pH and SIc and lower pCO2 in MJW than those in the other four springs; (Ca(2+) + Mg2+)/HCO(3-) of SJW, MJW and GB were nearly 1:1, dominated by carbonate rock weathering by carbon acid, while the (Ca(2+) + Mg2+) of DJ and TJZ was much higher than HCO3-, suggesting that sulfate and nitrate might also dissolve carbonate rock because of the agricultural activities; δ13C(DIC) was lighter in wet season because of the higher biological activities; the average δ13C(DIC) was in the order of DJ (-12.79 per thousand) < SJW (-12.48 per thousand) < GB (-10.76 per thousand)) < MJW (-10.30 per thousand) < TJZ (-6.70 per thousand), which demonstrated that δ13C(DIC) would be heavier after rocky desertification and lighter after the rocky desertification are treated and controlled.

[Contamination and ecological risk assessment of polycyclic aromatic hydrocarbons in surface sediment in karst underground river].

In order to understand pollution characteristics and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in surface sediment from Laolongdong underground river, the concentration and composition of 16 priority PAHs were analyzed. The results showed that the total concentrations of PAHs ranged from 58.2 to 3 598 ng x g(-1), and most of the values were between 100 and 5 000 ng x g(-1). It means that sediments in the river were moderately and heavily polluted by PAHs. The PAH composition were dominated by 2-4 rings (accounted for 75.1%) compounds in Laolongdong, while 4-6 rings PAHs accounted for 56.6% in Xiannvdong. Sediments in Laolongdong mainly came from the transportation of the upstream water and surface soil. 2 - 3 rings PAHs had higher transport capability with farther migration distance, while 4-6 rings PAHs had lower transport capability and shorter migration distance in the conduit, because 4-6 rings PAHs could be easily absorbed by sediments. The result of ecological assessment of PAHs showed that the ecological risk level in Laolongdong was low, leading to little negative ecological impact. However, the level in Xiannvdong was high. Once PAHs migrated from upstream to downstream, it would result in ecological threat for the downstream area.

[Nitrogen Fraction Distributions and Impacts on Soil Nitrogen Mineralization in Different Vegetation Restorations of Karst Rocky Desertification].

In order to illuminate the impact on soil nitrogen accumulation and supply in karst rocky desertification area, the distribution characteristics of soil nitrogen pool for each class of soil aggregates and the relationship between aggregates nitrogen pool and soil nitrogen mineralization were analyzed in this study. The results showed that the content of total nitrogen, light fraction nitrogen, available nitrogen and mineral nitrogen in soil aggregates had an increasing tendency along with the descending of aggregate-size, and the highest content was occurred in < 0. 25 mm. The content of nitrogen fractions for all aggregate-classes followed in the order of abandoned land < grass land < brush land < brush-arbor land < arbor land in different sample plots. Artificial forest lands had more effects on the improvement of the soil nitrogen than honeysuckle land. In this study it also showed the nitrogen stockpiling quantity of each aggregate-size class was differed in all aggregate-size classes, in which the content of nitrogen fraction in 5-10 mm and 2-5 mm classes of soil aggregate-size were the highest. And it meant that soil nutrient mainly was stored in large size aggregates. Large size aggregates were significant to the storage of soil nutrient. For each class of soil aggregate-size, the contribution of the nitrogen stockpiling quantity of 0. 25-1 mm class to soil net nitrogen mineralization quantity was the biggest, and following >5mm and 2-5 mm classes, and the others were the smallest. With the positive vegetation succession, the weight percentage of > 5 mm aggregate-size classes was improved and the nitrogen storage of macro-aggregates also was increased. Accordingly, the capacity of soil supply mineral nitrogen and storage organic nitrogen were intensified.

[Water-Sediment Partition of Polycyclic Aromatic Hydrocarbons in Karst Underground River].

Based on polycyclic aromatic hydrocarbons (PAHs) field data of dissolved phase and sediment phase, partition coefficient K(p) in sediment-water interface from Laolongdong underground river was obtained. The concentration of PAHs in water and sediment and partition coefficient K(p) in sediment-water interface were studied. The results showed PAHs concentrations were 81.5-8 089 ng x L(-1) with a mean value (1 439 ± 2 248) ng x L(-1) in water and 58.2-1 051 ng x g(-1) with an average (367.9 ± 342.6) ng x g(-1) in sediment. The dominant PAHs were 2-3 rings PAHs in water and sediment. However, high rings PAHs obviously enriched in the sediment. Partition coefficients varied from 55.74 to 46 067 L x kg(-1) in sediment-water interface, increasing with the rise of PAH compounds. All the organic carbon partition in sediment-water interface were higher than predicate values based on typical model of equilibrium distribution indicated that PAHs were strongly adsorbed in sediment. The linear free-energy relationship coefficient between K(oc) value and octanol-water partition coefficient K(ow) was 0.75, but the slope was lower than 1, indicating that sediment in Laolongdong underground river had weakly lipophilic characteristics and adsorption ability for PAHs.

[Source and contamination of polycyclic aromatic hydrocarbons in surface soil in karst underground river basin].

Surface soil (0-20 cm) from various agricultural sites in Laolongdong underground river basin was collected to determine the concentrations, compositional profiles, and sources of 16 priority polycyclic aromatic hydrocarbons (PAHs). PAHs were measured by GC/MC. The total concentrations of PAH16 ranged from 277-3 301 ng x g(-1), with a mean of 752.6 ng x g(-1) +/- 635.5 ng x g(-1), and 57%, 29% and 14% of soil samples were slightly, moderately and heavily polluted by PAHs, respectively. The PAH compositional profiles were dominated by 2,3 ring compounds, which accounted for 28.72% -72.68% (a mean of 48.20%) of the total PAHs, while 4 ring and 5,6 ring PAHs accounted for an average of 7.77% and 34.03%, respectively. Soil organic matter (SOM) was found to be significantly correlated with the 16 PAHs and total PAHs. However, pH value was slightly correlated with the 16 PAHs and total PAHs. Isomer pair ratios and Principal component analysis (PCA) suggested vehicles, coal, petroleum and biomass combustion as the main sources of PAHs, and another major source was petroleum.

[Investigation of nitrogen, phosphorus and microbial contamination in Laolongdong underground river system of Chongqing].

With urbanization, groundwater in China has been widely polluted. Karst groundwater is important in southwest China, and would be difficult to recover once contaminated. NO3(-), PO4(3), NH4(+), total coliform, total E. coli and fecal coliform were chosen as indexes in the study of groundwater of Laolongdong Underground River System in Nanshan Mountain, Chongqing. After a few years of survey, the results showed that NO3(-), NH4(+) and PO4(3-) concentrations in the water were all above the nature value, especially NH4(+) and PO4(3-). The NO3(-) concentration of Guihuawan spring ranged from 19.78-68.55 mg x L(-1), in some months, above the recommended water quality guideline (50 mg x L(-1)) according to Standards for Drinking Water Quality set by World Health Organization. NH4(+) and PO4(3-) concentrations in Laolongdong underground river varied from 2.71-12.92 mg x L(-1) and 0.16-11.22 mg x L(-1). The NO3(-) concentration in Laolongdong underground river was lower than in karst spring; however, the concentrations of NH4(+) and PO4(3-) were higher than in the spring. It seemed that the NO3(-) concentration tended to decrease from 2008 to 2013 in the underground river caused by urbanization, reduction of farmland and reducing environment. However, waste water with a high PO4(3-) concentration led to an increasing trend in the PO4(3-) concentration in underground river. Microbial contamination was extremely serious, and even far exceeded class V of water quality standards of China. For example, the concentration of fecal coliform in the groundwater ranged from 3.4 x 10(4)-3.68 x 10(4) CFU x mL(-1). Because of the special hydrogeological structure, karst depressions, skylights and sinkholes can lead pollutants easily to the underground water. Agriculture activity, sewage from towns, enterprises and residential areas were the major sources of nitrogen, phosphorus and microbial contamination.

[Variation characteristics and environmental significant of trace elements under rainfall condition in karst groundwater].

Chemical dynamics of Qingmuguan karst groundwater system were continuously monitored during the rainfall events. A series of high-resolution concentrations data on trace elements, such as barium, strontium, iron, manganese, aluminum, and other major elements were acquired. Correlation analysis and analysis of concentration curve were employed to identify the sources and migration path of the trace elements. And the formation process of trace elements in groundwater was discussed with the geological background of underground river basin. Research shows that barium and strontium derived from carbonate dissolution appeared to be stored in features such as fissures and pores. These two ions were recharged into the underground river by diffusion during precipitation, which resulted in small changes in the their concentration. However total iron, total manganese and aluminum derived from soil erosion varied relatively widely with strong response to rainfall, attributing to the migration of total iron and aluminum with overland flow to recharge the subterranean river directly via sinkholes while total manganese via soil-rock porous media. The results showed that concentrations of all the five trace elements were below 1 mg x L(-1), and the highest concentrations of total iron, total manganese and aluminum exceeded the limit of drinking water. To some extent, the concentrations of total iron and aluminum may be an indicator for soil erosion and water quality.

[Contamination and ecological risk assessment of polycyclic aromatic hydrocarbons in water and in Karst underground river catchment].

Water samples in Laolongdong underground river catchment were collected to determine the concentration, compositional profiles, and evaluate ecological risk of 16 priority polycyclic aromatic hydrocarbons (PAHs). PAHs were measured by GC/MS. The total concentrations of 16 PAH ranged from 81.5-8019 ng · L(-1) in underground river, 288.7-15,200 ng · L(-1) in karst springs, and 128.4-2,442 ng · L(-1) in surface water. Affected by waste water from Huangjueya town, concentrations of PAHs in underground river were higher than those in surface water and waste water from sinkhole. The PAHs profiles were dominated by 3 ring PAHs. There were differences of monthly variations of PAHs contents in the water, due to waste water, season and different characteristics of PAH. Surface water and waste water from sinkhole played an important role on contamination in the river. The levels of ecological risk were generally moderately polluted and heavily polluted according to all detected PAH compounds in the water.

[Temporal-spatial variations of total nitrogen in the degraded grassland of Three-River Headwaters region in Qinghai Province].

Based on the data of the second soil survey and field sampling in 2009 and 2010, temporal-spatial variations of total nitrogen (TN) in the degraded grassland 0-10 cm, 10-20 cm and 30-50 cm beneath the surface soil at the Three-River Headwaters region in Qinghai Province for a 30-year period (1980-2010) were evaluated using geostatistics and geographic information system (GIS). After exclusion of the outliers, the results showed a downward trend from the surface to the bottom in the mean TN values measured in the samples collected during the two periods. For the same soil layers, the average TN contents and the coefficient of variation in 1980 were higher than those in 2010. The TN contents of the two periods showed a log-normal distribution. Semivariograms analysis of the experiments indicated that the nugget effect in the same soil layer was lower in 2010 than in 1980; suggesting that the spatial distribution autocorrelation of TN in the Three-River Headwaters region in Qinghai Province was strengthened and structural factors played a more and more important role on the spatial distribution of TN. The results of ordinary kriging showed that there were regional differences in variations of the total nitrogen content. There were significant decreases in the southern, central and eastern regions, while the increase mainly occurred in the western areas.