Study on the structure and hydrological cycle of the Pingjiang underground river system.

The connectivity of the Barat Cave underground river system needs to be known to support the implementation of proper environmental management so that water resources can be maintained sustainably. However, the mapping of underground river paths is often hindered by conditions of narrow cave passages, a barrier blocking the flow of water (siphon), deep underground lakes, underground waterfalls, as well as paths filled with water. This research was conducted in Barat Cave, Karangbolong Karst Area. The purpose of this study is to determine the upstream-downstream connectivity system in this underground river and define the characteristics of the passageway based on quantitative analysis of the transport parameters from the tracer test results. This underground river network analysis needs to be done because previous research has never analyzed this underground river network. The research method used in this study is divided into three stages, namely the pre-field stage, the field stage, and the post-field stage. The pre-field step includes determining the location of the study, collecting secondary data, and studying the literature. The field stage consists of a hydrogeological survey to find information on the presence of caves, springs, sinking stream ponors, or luweng in the study area, instantaneous discharge measurements, and tracer tests. The post-field stage includes data processing and analysis. The results showed that the Barat underground river system originated from the Kalimas sinking stream, Mblabak Cave, Pendok Cave, and Pagilangan sinking streams, then merged into a single tunnel without a flow breaker to the Barat Cave, Pengantin Cave, and appeared in the Kalikarak springs to become a surface river, with a tunnel pattern in the form of curvilinear branchwork. The transport parameters for the underground system tracing of the Barat cave have an advection value of 86.528 m/hour, a dispersion of 0.092 m2/second, a dispersivity of 3.38 meters, and a recovery of 63%. The transport value of the tracing test parameter is influenced by the characteristics of the passageway and underground river flow conditions.

The aim of this study was to determine the sources and contamination characteristics of polycyclic aromatic hydrocarbons (PAHs) in various environmental media in a karst underground river system. For this purpose, air, underground river water, sediment, and soil samples were collected from a typical underground river in southern China in the dry and wet seasons of 2013–2014, and the compositional spectra, distribution, and ratio characteristics of 16 PAHs were determined for comparative analysis. The results show that three 2–3-ring PAHs (naphthalene, phenanthrene, and fluoranthene) mainly occur in air and underground river water. In sediments and soils, 4–6-ring PAHs are the main components. The PAH concentrations in the air in the wet season are clearly greater than those in the dry season, while it is the opposite in the underground water. Seasonal differences in the concentration of PAHs in the sediments and soils are minor. The concentrations of PAHs in the environmental media overall showed variation in the following order: upstream < midstream < downstream, and this is related to pollutant discharge, adsorption, etc. The main source of PAHs in the upstream area is the combustion of grass, wood, and coal, while it is petroleum in the midstream area, and combustion of grass, wood, coal, and petroleum near the outlet of the underground river. It is necessary to change the energy structure in the study area, improve the efficiency of environmental protection facilities, reduce the emission in vehicle exhaust, and control pollution by PAHs at their sources.

Karst areas have much higher ecological vulnerability and are easy to be contaminated by polychlorinated biphenyls (PCBs) which are introduced as health risk pollutants. PCBs concentrations were used to understand the transport behavior of PCBs conducted in the karst Nanshan Underground River, China. Water and sediments from the underground river water, and sediments and soil from the surface of the corresponding watershed were collected monthly in 2011 and 2012 and PCBs were analyzed. Seasonal variations were found in concentrations of PCBs both in the waters and sediments. PCBs concentrations varied from 0.3 to 29.9 ng·L−1 in the groundwater, while from 0.1 to 366.1 ng·g−1 in the underground sediments. Correlations were found in concentrations of PCBs in waters and sediments between the underground river and surface systems which indicate that the surface systems play a major role for the transport of PCBs and contamination in the underground river systems. Karst features are liable for the transport behavior. The underground river waters transport PCBs at mean 3 g·day−1.

Hydrochemical fingerprints of karst underground river systems impacted by urbanization in Guiyang, Southwest China

The goal of this study is to understand the impact of human activities on the characteristics of chemicals and heavy metals in typical karst subterranean rivers in South China and the patterns of their changes. Thus, the Jila, subterranean river in Liuzhou, the Lihu subterranean river in Nandan and the Maocun village subterranean river in Guilin in karst regions in Guangxi Province and the Banzhai subterranean river in Maolan in a karst region in Guizhou Province were selected for analysis. These four rivers are typical subterranean rivers and are affected by human activities to different extents. During October–December 2015 (dry season), we performed on-site investigations and collected water samples. The results show the following: (1) Ca2+ and HCO3− are significantly correlated with the heavy metals Cr and Ni in the four subterranean rivers (p < 0.01); this relationship is mainly attributed to rock weathering from dissolution but is caused mostly by human activities. (2) The detected concentrations of K+, Na+, NH4+, Cl− and SO42− are significantly correlated with the detected concentrations of NO3− in the four subterranean rivers (p < 0.01); domestic sewage, pesticides and fertilizer are the main sources. (3) The dilution from precipitation results in decreases in the ion concentrations, but the NO3− and SO42− concentrations following dilution from precipitation are still high, suggesting that domestic sewage and the application of fertilizer continuously impact the subterranean rivers. (4) Conductivity is an important index that reflects the status of land usage and water quality; the conductivity levels increase with anthropogenic disturbances. (5) The comparison of previously published ion concentrations in the Jila subterranean river in Liuzhou with those measured in this study shows that pollution has decreased substantially, which is closely related to urban planning and enhanced environmental consciousness in this region. The above results and conclusions can provide a scientific basis for the optimal management of water resources in the karst regions in South China and the improvement of water quality for subterranean rivers.

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.

Speciation, distribution and migration pathways of polycyclic aromatic hydrocarbons in a typical underground river system in Southwest China

A hydrogeochemical and isotopic study was conducted on the subterranean karst stream, namely the Guancun subterranean stream (GSS). The hydrogeochemical processes of the GSS were controlled through calcite dissolution and precipitation and were driven by the concentration of CO2, which controlled changes in the pH and of PCO2 in the water. The δ18O and δD values of the GSS were within the global meteoric water line and the local meteoric water line, thereby indicating that the water of the GSS comes from precipitation. Certain abnormal δ18O and δD values suggest the effect of evaporation on the GSS given its use in a particular irrigation system, wherein the GSS in transformed into a surface stream and flows for a relatively long time on the surface during the wet season. The δ13CDIC values of the GSS range from −13.5 to −11.3‰ in the dry season and from −13.9 to −9.5‰ in the wet season, thereby indicating that the GSS belongs to a semi-open system. The δ13CDIC values in the GSS were formed by the δ13CDIC values of the soil CO2 and carbonate dissolution at different proportions. According to the simplified mass balance formula, the contributions of carbonate dissolution to the dissolved inorganic carbon (DIC) of the GSS were calculated to be 50.2–58.3% and 48.7–64.7% in the dry and wet seasons, respectively, thereby indicating a less than 50% carbonate dissolution contribution during the formation of DIC in karst groundwater. Moreover, sulfuric acid and nitric acid were observed to participate in karst processes.

At Tahe Oilfield Ordovician strata, caves and underground rivers are the commonly developed geological structures…. Caves and underground rivers serve as connection pipes for different types of reservoirs, and are also an important part of a reservoir. This paper presents the researched carried out on a block of high resolution 3D seismic data from Tahe oil field. For the research, Absorption quality factor attribute (AQF) was tested with the aim of identifying the cave and underground river systems. In the AQF attribute sections, the caves were depicted clearly and some inconspicuous dot-like seismic reflection and some seismic reflection troughs were better displayed. In addition, the original seismic, similarity attribute data, body sculpting technology and drilling data successfully verified the caves which were predicted from the AQF data. Our research shows that AQF attribute identifies the caves and underground river systems very well. Hence, AQF attribute is useful in identifying and dividing caves and underground river systems.

The effect of heavy rainfall events on nitrogen patterns in agricultural surface and underground streams and the implications for karst water quality protection

In the Lungu area of the Tarim Basin, a large number of karst fracture-cavity reservoirs associated with the subterranean rivers are developed in the ancient buried hills of the Ordovician carbonate rocks. These are the main oil and gas production targets in the area. The reservoirs in the paleo-aqueous system are strong heterogeneity in both vertical and horizontal directions, therefore, identifying and predicting the characteristics of the underground river system is one of the effective ways to improve the success rate of oil and gas exploration and development. To analyze the seismic response characteristics of different shapes, sizes and filling degrees underground river reservoirs. This paper focuses on get forward seismic profiles based on three-dimensional forward modeling method of artillery domain wave equations, which using various types of underground river geology models that established from seismic, logging and drilling data. The forward simulation results show that the length, height, fillings, and surrounding rock factors of the underground river all influence the seismic reflection characteristics. The forward modeling results supported the implement of the spatial distribution of the ancient underground river system and the development of high-quality fracture-cavity reservoirs. In addition, it provided theoretical guidance to the interpretation and prediction of the fractured-cavity reservoirs related to the underground river systems.KeywordsCarbonate rocksAncient subterranean river systemThree-dimensional forward modelingLungu area

Karst areas have much higher ecological vulnerability and are prone to be contaminated. Organochlorine pesticides (OCPs) were detected in waters and sediment from the two sites of the karst Nanshan underground river system, China, to understand the sources and transport of OCPs in the underground river systems. Obviously, seasonal variations were found both in the waters and the sediments. Detected OCPs ranged from 61 to 936 ng L−1 in the groundwaters and 51–3,842.0 ng g−1 in the underground sediments, respectively. OCPs in groundwaters were mixture of younger and older residues from commercial sources. The maximum OCPs in the sediments of the underground river were historically older residues from commercial sources. The sources of OCPs in the waters and sediments of the underground river indicated that the surface systems play an important role in OCPs transport and pollution in the underground river. Karst features were liable for the transport behavior.

This study presents an investigation of the hydrogeochemical processes and potential vulnerability of a typical underground river system in southwest China. Physical and chemical data were collected from both traditional manual sampling and continuous automatic monitoring. Analysis of high-frequency monitoring data from the outlet spring, Jiangjiaquan spring (JJQ), of the underground river system suggests the existence of several physico-chemical processes with distinctive characteristic response to storm events. Due to the impacts of sources and migration influencing factors, seasonal variations of major chemical components of the outlet spring are much different. For the entire karst watershed, spatial variability of surface and subsurface water geochemistry was significantly influenced by land use and lithologic characteristics. Principal component analysis (PCA) reveals that agricultural activities, water-rock interactions and soil erosion are potential influencing factors and the main sources for the chemical composition of JJQ spring. Nutrients from agricultural activities can be brought into the underground river by ways of diffuse recharge from leaching of soils, as well as focused recharge from surface flow via sinkholes. Water-rock interactions in the karst aquifer provide the evidence of diffuse recharge that contributed to groundwater quality. Soil erosion mainly causes focused recharge of contaminated water with particulate matters including iron, manganese and aluminum that carried into the underground river from sinkholes via surface flow.

Water samples from the two underground rivers (Fenghuang River and Longju River) and samples of the dry and wet deposition of atmospheric dissolved inorganic nitrogen were taken from the Longfeng karst trough valley located in the Zhongliang mountain in the suburbs of Chongqing from May 2017 to April 2018. Anions, cations, δ15 N(NO3-), δ18 O(NO3-), δ18 O(H2O), and δ13C(DIC) isotope data were used to investigate the NO3- source and its environmental effects. The results showed:① The hydrochemistry of the two underground rivers is of the type HCO3-Ca. The NO3- concentration varied from 17.58 to 32.58 mg·L-1, with an average of 24.02 mg·L-1, and was slightly higher in rainy season than the dry season, revealing that the underground rivers were polluted. ② The δ15 N(NO3-) value ranged from -3.14‰ to 12.67‰, with an average value of 7.45‰. The δ18 O(NO3-) value ranged from -0.77‰ to 12.05‰ with an average value of 2.90‰, and was higher in the dry season than the rainy season, indicating that animal excreta and domestic sewage were main NO3- sources throughout the year. In addition, rainfall, fertilizer, and soil nitrogen were the NO3- sources during the rainy season. There are no significant differences between the NO3- sources of the two underground rivers, and nitrification is the main nitrogen conversion process. ③ The molar ratio of (Ca2++Mg2+)/HCO3- varied from 0.65 to 0.82. That of the Fenghuang River was 0.75 and that of the Longju River was 0.70. The δ13C(DIC) value ranged from -12.46‰ to -9.20‰, with a mean of -11.10‰ in the Longju River and -10.72‰ in the Fenghuang River. These values indicated that the HNO3 derived from the nitrification of NH4+ was involved in the weathering of carbonate rocks. ④ HNO3 dissolved carbonate rocks and aggravated the chemical weathering of carbonate rock in the basin, contributing 8% of the DIC in groundwater, and 9% and 7% in Fenghuang River and Longju River, respectively.

Determining the origins and history of sedimentation in an underground river system using natural and fallout radionuclides