[Sources and Variation Characteristics of Dissolved Lipid Biomarkers in a Typical Karst Underground River].

Water samples in Qingmuguan underground river were collected to determine the concentration of dissolved lipids, and their sources, composition and migration characteristics in underground river were studied. The results were obtained as follows. (1) The average content of various dissolved lipids decreased with increasing distance of migration in Qingmuguan underground river, and the most distinctive was dissolved saturated straight chain fatty acids with its content decreasing by about 81.71%, from the initial 5,704 ng · L⁻¹ to 1,043 ng · L⁻¹. (2) N-alkane could indicate the sources of dissolved organic matter in underground river, but saturated straight chain fatty acid and fatty alcohol had the advantage in indicating algae, bacteria and other microorganisms. (3) With the increasing migration distance of Qingmuguan underground river, the input type of dissolved organic matter in underground river was different, which might be resulted from the heterogeneity of karst surface. (4) In ternary plot of alkane sources, aquatic plants constituted the major contribution of dissolved organic matter in Qingmuguan underground river, followed by higher plant, algae/ bacteria. Unlike higher plants and algae/bacteria, the contribution from aquatic plants decreased with increasing migration distance of underground river. (5) To a certain extent, TAR (alkane) values could reflect the rainfall, and the values of CPI, L/H in saturated straight chain fatty acids might indicate the degradation activities of bacteria.

[Distribution Characteristics and Source Identification of Polycyclic Aromatic Hydrocarbons, Fatty Acids in Water of Karst Underground River].

In order to explore the contents, composition, distribution characteristics, sources and pollution level of polycyclic aromatic hydrocarbons(PAHs) and fatty acids in water of Qingmuguan karst underground river in Chongqing, water samples were respectively collected from underground river in rainy season and dry season, 2013 and polycyclic aromatic hydrocarbons, fatty acids of the water samples were quantitatively analyzed by Gas Chromatography-Mass Spectrometer(GC-MS). The results showed that the contents of PAHs and fatty acids in water of Qingmuguan karst underground river ranged from 77.3 to 702ng·L-1 and 3302 to 45254 ng·L-1, respectively. In terms of composition, the PAHs profiles were dominated by (2-3) rings PAHs in water samples, which accounted for more than 90% of the total PAHs contents, while the carbon numbers of fatty acids ranged from C10 to C28, and fatty acids profiles were dominated by saturated straight chain fatty acids, followed by mono-unsaturated fatty acids. In terms of the distribution characteristics, the contents of PAHs had minor difference at each sample point in water of underground river in rainy season. At the entrance, exposed and exits, the contents of fatty acids reduced in turn, moreover the contents of fatty acids were close at the exposed and exits. dry season:at the entrance, exposed and exits, the contents of PAHs in water of underground river decreased firstly and then increased. The contents of fatty acids were close at each sample point in water of underground river. As a whole, the contents of PAHs and fatty acids in water of underground river in rainy season were significantly higher than those in dry season. Source analysis indicated that the PAHs in water of Qingmuguan underground river were mainly originated from the combustion of coal and biomass (wood, crop straw, etc) at the underground river catchment. The fatty acids were mainly originated from aquatic algae (diatoms and green alga, etc), and bacteria, with the contribution of aquatic algae dominated. The water of underground river was suffered the middle to mild pollution by PAHs, and compared with the dry season, the rainy season was more severely polluted.

[Fecal Contamination in Laolongdong Underground River as Measured by the Sterol Biomarkers].

To investigate whether the underground river was polluted or not, and trace the source of fecal sterols, the particulate water samples were collected from typical karst underground river named Laolongdong in Nan'an District, Chongqing Municipality in October, 2014, January, March and May, 2015. Ten prior steroids in the underground river were quantitatively analyzed by the gas chromatography-mass spectrometer (GC-MS). The results showed ten steroids including 9 sterols and 1 ketone were detected. During the sampling period, the mass concentrations of particulate steroids (ranging between 1573 and 5007 ng·L-1) in March and May were higher than those in October and January. The 3 principal steroids-cholesterol, ß-sitosterol and coprosterol-in the river accounted for 50.8%-80.4% of the total steroids. The ratios of (epicoprostanol+coprostanol) to (coprostanol+epicoprostanol+cholestanol) of three samples were greater than 0.7, which indicated the river was contaminated in sampling months. The ratio of epicoprostanol to coprostanol was less than 0.2 in October, which indicated the wastewater came from the upstream sewage treatment plant. The ratios of coprostanol to ΣSteroids and coprostanol to 24-ethylcoprostanol in January, March and May were respectively 0.109-0.254 and 6.3-10.3, which indicated that Laolongdong underground river was mainly polluted by human feces. The ratio of 24-ethylcoprostanol to 24-ethylcholestanol in March (0.86) was less than those in January (5.4) and May (2.3), which showed the river was polluted more severely in March than in January and May by poultry dung.

[Impact of Urbanization on the Sources of Dissolved n-alkane in Underground River].

To investigate the influence of urbanization on the component features of dissolved n-alkanes (D-ALK) in the underground river in the dry season, water samples were collected respectively at the outlet of the two underground rivers. Components of D-ALK in these samples were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the distribution of D-ALK carbon number at the two sites ranged from nC14 to nC35 in dry season. The total concentration of D-ALK (DT-ALK) in Jiangjia spring ranged from 102 to 356 ng·L-1, with an average of 230 ng·L-1. The low-number carbons were predominant in December 2014, January and April 2015. The ratios of LMH/HMH (nC21-/nC22+) ranged from 2.0 to 10. The carbon preference index (CPI) between nC14 and nC25 ranged from 0.19 to 0.57, with a maximum of C16 (Cmax16). However, in November 2014, February and March 2015, these samples had a bimodal distribution in n-alkane. All of the CPI14-25 and the ratios of LMH/HMH were less than 1. The CPI24-35 ranged from 1.2 to 23 with the Cmax 31 or Cmax33. During the three months, the values of Paq were 0.2, 0.7 and 0.1, respectively. The alkane indexes (AI) in November 2014 and March 2015 were 0.95 and 0.98, respectively. The values of DT-ALK in Laolongdong ranged from 110 to 697 ng·L-1 with an average of 310 ng·L-1. The carbon number distribution of each month had a low predominance, and the CPI14-25 was less than 1. In the dry season, under the influence of different human activities, the content and component of D-AKL in Laolongdong which originated mainly from microorganisms was more stable than that in Jiangjia spring, which was mainly derived from microorganisms and a mixture of microorganisms and plants.

[Comparison Study of the Alkanes in Different Aquifer Medium Under Qingmuguan Underground System].

Dissolved alkanes were collected from Dalv spring and Jiangjia spring from July to November, 2013, and were quantitatively analyzed by the gas chromatography-mass spectrometer (GC-MS). The results show that the total content of dissolved alkanes in Dalv spring is 175-3279 ng x L(-1), with a mean value of 1011 ng x L(-1). In Jiangjia spring, the total content of dissolved alkanes is 282-775 ng x L(-1), with a mean value of 527 ng x L(-1). Ratios of the content of alkanes with high carbon number( C25-C32) to the total alkanes vary from 27.89% to 52.92% in Dalv spring, and 23.66% to 49.73% in Jangjia spring. Combined with CPI and OEP the relative contribution to the dissolved alkanes of higher plants are increasing in Dalv spring, however, it is different in Jiangjia spring. In addition, the values of L/H couldn't reflect different organic contributions to the dissolved alkanes, and the values of TAR may relate with rainfall.

[Difference of Karst Carbon Sink Under Different Land Use and Land Cover Areas in Dry Season].

In order to identify the distinction of soil CO2 consumed by carbonate rock dissolution, Baishuwan spring, Lanhuagou spring and Hougou spring were selected as objects to monitor the hydrochemistry from November 2013 to May 2014. The results showed that the highest HCO3- concentration was observed in Baishuwan spring which is covered by pine forest, while the lowest HCO3- concentration was observed in Hougou spring which is mainly covered by cultivated land. In Baishuwan spring, HCO3- was mainly derived from carbonic acid dissolving carbonate rock and the molar ratio between Ca(2+) + Mg2+ and HCO3- was close to 0. 5; while the molar ratio between Ca(2+) + Mg2+ and HCO3- exceeded 0.5 because the carbonate rock in Lanhuagou spring and Hougou spring was mainly dissolved by nitric acid and sulfuric acid. Because of the input of litter and the fact that gas-permeability of soil was limited in Baishuwan spring catchment, most of soil CO2 was dissolved in infiltrated water and reacted with bedrock. However, in Lanhuagou spring catchment and Hougou spring catchment, porous soil made soil CO2 easier to return to the atmosphere in the form of soil respiration. Therefore, in order to accurately estimate karst carbon sink, it was required to clarify the distinction of CO2 consumption by carbonate rock dissolution under different land use and land cover areas.

[Variation Characteristics and Sources of Heavy Metals in an Urban Karst Groundwater System during Rainfall Event].

The groundwater discharge and heavy metal concentrations (Mn, Pb, Cu and As) at the outlet of Nanshan Laolongdong karst subterranean river, located at the urban region in Chongqing, were observed during the rainfall events. Analysis of flow and concentrations curves was employed to study their responses to the rainfall events and explore the internal structure of karst hydrological system. Principal component analysis (PCA) and measurements were used to identify the sources of heavy metals during rainfall. The result showed that the discharge and concentrations of the heavy metals responded promptly to the rainfall event. The variation characteristics of flow indicated that Laolongdong subterranean river system belonged to a karst hydrological system including fractures together with conduits. Urban surface runoff containing large amounts of Mn, Pb and Cu went directly to subterranean river via sinkholes, shafts and karst windows. As a result, the peak concentrations of contaminants (Mn, Pb and Cu) flowed faster than those of discharge. The major sources of water pollution were derived from urban surface runoff, soil and water loss. Cave dripwater and rainwater could also bring a certain amount of Mn, Pb and As into the subterranean river. Urban construction in karst areas needs scientific and rational design, perfect facilities and well-educated population to prevent groundwater pollution from the source.

[Sources, Migration and Conversion of Dissolved Alkanes, Dissolved Fatty Acids in a Karst Underground River Water, in Chongqing Area].

Dissolved alkanes and dissolved fatty acids were collected from Qingmuguan underground river in July, October 2013. By gas chromatography-mass spectrometer (GC-MS), alkanes and fatty acids were quantitatively analyzed. The results showed that average contents of alkanes and fatty acids were 1 354 ng.L-1, 24203 ng.L-1 in July, and 667 ng.L-1, 2526 ng.L-1 in October respectively. With the increasing migration distance of dissolved alkanes and dissolved fatty acids in underground river, their contents decreased. Based on the molecular characteristic indices of alkanes, like CPI, OEP, Paq and R, dissolved alkanes were mainly originated from microorganisms in July, and aquatic plants in October. Saturated straight-chain fatty acid had the highest contents in all samples with the dominant peak in C16:0, combined with the characteristics of carbon peak, algae or bacteria might be the dominant source of dissolved fatty acids.

[Sources, Migration and Conversion of Dissolved Sterols in Qingmuguan Underground River].

Water samples were collected from the Qinmuguan underground river from July to November in 2013. By gas chromatography-mass spectrometer (GC-MS), dissolved sterols were quantitatively analyzed. The results show that the average variation content of dissolved sterols ranges from 415 to 629 ng x L(-1), with the increasing migration distance of dissolved sterols in underground river, its contents are decreased. Between the inlet and outlet of Qingmuguan underground river, the average variation contents of dissolved sterol are between 724 and 374 ng x L(-1), and the average variation ratios of the content of stigmasterol with cholesterol range from 0.29 to 0.12. In short, their values are decreased accompanied by the increasing migration distance of underground river. The composing component in dissolved sterols varied differently between July to December, and the main component of dissolved sterols is cholesterin, the ratios of the content of dissolved sterols with cholesterin to the total dissolved sterols range from 37.30% to 94.85%. In addition, the ratios of the content of dissolved sterols with coprostanol to cholesterin, coprostanol to cholesterin are below 0.2 respectively, indicating the water quality of underground river is not contaminated by domestic sewage, but with the passage of time water quality tends to deterioration.

[Variation Characteristics and Sources of Polycyclic Aromatic Hydrocarbons in Karst Subterranean River During Rainfall Events].

The water samples were continuously collected at the outlet of Nanshan Laolongdong subterranean river basin, which is located in Chongqing, during the rainfall event in June 2014. Sixteen priority polycyclic aromatic hydrocarbons (PAHs) in water were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The objectives of this study were to reveal the variation characteristics and sources of PAH16 in karst subterranean river during the rainfall event. The results showed that the subterranean river responded promptly to the rainfall, and there were four peaks of the total concentrations of PAH16, two peaks occurred during the flow rise stage, the others were in the maximum flow and flow decline stages. The total concentrations of PAH16 ranged 101-3 624 ng x L(-1), with a mean of 578 ng x L(-1), the total concentrations of 7 carcinogenic PAHs ranged ND-336 ng x L(-1), with a mean of 31.1 ng x L(-1). The PAH compositional profiles were dominated by 2,3-ring compounds, which accounted for 86.17% of the total concentrations of PAH16. The total concentrations of PAH16 were most influenced by the rainfall, through the cleaning of atmospheric pollutants by the rain and the scouring of the surface contaminants by the rainfall runoff. The PAHs in water mainly originated from the incomplete combustion of petroleum products and fossil fuels such as coal, as well as natural digenetic process. Compared to other areas in the world, the concentrations of PAH16 were generally at moderately polluted and heavily polluted levels.