Urbanization and agriculture intensification jointly enlarge the spatial inequality of river water quality.

Rivers are severely polluted by multiple anthropogenic stressors. An unevenly distributed landscape pattern can aggravate the deterioration of water quality in rivers. Identifying the impacts of landscape patterns on the spatial characteristics of water quality is helpful for river management and water sustainability.

[Sources and Biogeochemical Processes of Nitrate in the Laolongdong Karst Underground River Basin, Chongqing].

Samples of sewage, well water, and underground river water of the urbanized Laolongdong karst underground river basin in Chongqing, China were collected during July 2019 and October 2020 and measured to determine the nitrate origin and biogeochemical processes based on geochemistry and dual nitrate isotope (N-NO and O-NO) data. The results showed that:① the isotopic nitrate compositions of sewage ranged from -3.3‰ to 14.

Nitrate fate and decadal shift impacted by land use change in a rural karst basin as revealed by dual nitrate isotopes.

Nitrate pollution in oxygenated karst aquifers is common due to nitrification and anthropogenic inputs. However, the shift of nitrogen sources influenced by enhanced rural tourism activities and land use changes are not well understood. In this study, hydrochemistry and dual nitrate isotopes of water samples from a rural karst basin in Chongqing, southwestern China were employed to investigate the nitrate fate and its decadal change during the periods from 2007-2008 and 2017-2019.

Integrated understanding of the Critical Zone processes in a subtropical karst watershed (Qingmuguan, Southwestern China): Hydrochemical and isotopic constraints.

Improving the management and protection of karst groundwater resources and addressing karst-related environmental and ecological problems still face challenges raised from the limited knowledge on the entire karstic Critical Zone (K-CZ), including soil, epikarst, the vadose and saturated zones. Particularly, there is still a lack of integrated understanding of K-CZ properties and major CZ processes across space and time. In this study, we measured and analyzed the hydrochemical and multiple stable isotopic compositions of soil water, surface- and groundwaters from various compartments of the K-CZ in a typical subtropical karst watershed - Qingmuguan (QKW), Southwestern China, in order to explore the source and spatiotemporal variations of water and solutes (C, N, S) within the K-CZ; thereby elucidating the hydrological and biogeochemical processes and their affecting factors.

Nitrate sources and biogeochemical processes in karst underground rivers impacted by different anthropogenic input characteristics.

Nitrate is one of the most common pollution sources in groundwater, particularly in highly vulnerable karst aquifers. The potential for nitrification and denitrification within karst aquifers varies in different settings depending on the extent of anthropogenic inputs, so that accurate identification of nitrate sources can be difficult. Geochemical data and dual nitrate isotopes were measured in this study, incorporating a Bayesian isotopic mixing model, and used to identify nitrate sources, nitrification and denitrification, and quantitatively determine nitrate sources under different extents of anthropogenic inputs in three karst catchments within Chongqing Municipality, SW China: Laolongdong (an urbanized area), Qingmuguan (a suburban village), and Shuifang Spring (a protected natural area).

Nitrate migration and transformations in groundwater quantified by dual nitrate isotopes and hydrochemistry in a karst World Heritage site.

Karst aquifers are extremely vulnerable to pollution, including from nitrate. This research advances a systematic evaluation of water quality dynamics and processes in a relatively pristine karst flow system impacted by seasonal tourism, in particular migration and transformation of nitrate. Water samples from the Shuifang Spring basin (Jinfoshan Karst World Heritage Site, Chongqing, China) were collected for analysis of ion concentrations and dual nitrate isotopes.

[Comparison of the Geochemical Characteristics of Karst Springs of a Vertically Zoned Climate Region under Human Activity: A Case of Shuifang Spring and Bitan Spring in the Jinfo Mountain Area, Chongqing].

To investigate the hydrochemical variation of karstic groundwaters in a vertically zoned climate region affected by human activity, Shuifang Spring and Bitan Spring in the Jinfo Mountain area of Chongqing were selected as a study site. Based on the differences between the natural state and intensity of human activity of these two springs, their hydrogeochemical characteristics and the controlling factors on karstic groundwaters were analyzed by means of independent sample tests, the Gibbs graphic method, principle component analysis (PCA), and geochemical susceptivity analysis. The results show that differences in karst development in the vertical climatic zone leads to higher total ion concentrations in Bitan Spring than in Shuifang Spring.

Coupled hydrogeochemical evaluation of a vulnerable karst aquifer impacted by septic effluent in a protected natural area.

Karst aquifers are highly vulnerable to pollution from human activities. Among sources of these contaminants, septic tank effluent can easily pollute karst aquifers, especially concentrated inputs such as those, for example, from tourist hotels. However, the impacts of septic effluent from relatively large, concentrated inputs on karst aquifers have seldom been assessed previously and therefore provide the focus of this study.

[Nitrate-Nitrogen Pollution Sources of an Underground River in Karst Agricultural Area Using N and O Isotope Technique].

The objectives of this study were to reveal the sources of nitrate and the ratio of karst in an agricultural basin based on a N and O isotope technique and quantitative calculation of the IsoSource model. From May to October 2017, six sampling points in the Qingmuguan river basin, Chongqing, were monitored every 24 d. Results showed that there was a great risk of nitrate pollution in the underground river system, because most NO-N concentrations of the sampling points exceeded the threshold.

[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 -test and principal component analysis(PCA), the results showed that ions of Ca, HCO, Mg, K, NO, Na, SO, 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, NO, but ions of Na, SO, Cl showed an opposite trend.

[Characteristics and Resources of Fly Ash Particles in the Snowpack of Jinfo Mountain, Chongqing].

Snow can preserve the atmospheric information, which makes it become a good media in studying regional environment. Jinfo Mountain with an elevation of 2251.1 m, located at the transition zone between Sichuan basin and Yunnan-Guizhou Plateau, is deeply affected by human activities, and snowfall is the main form of precipitation during the winter.

[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.

[Influences of Biological Processes on Geochemical Characteristics: An Example of a Mountain Karst Pool in Spring Season].

Karst hydrologic system is quite sensitive to the surrounding environment, which leads to changes in the quality of karst water within diel, hours even minutes. Many surface water undergoes changes of pH value, dissolved gas, trace elements, nutrition and other hydrochemical parameters in a daily timescale. The Shuifang spring and its draining pool are located in Jinfo Mountain in Chongqing, the middle karst mountain belonging to temperate climate with an elevation of about 2050 m a.

[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.

[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.

[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.

[Research on the sensitivity of geochemical of underground river in Chongqing Xueyu Cave].

Quoted geochemical susceptivity index and isosensitive line on geochemical susceptivity, analyzed the data of underground rivers of Xueyu Cave in Chongqing from September 2010 to August 2011, we found that the chemical composition of the underground river was controlled by the bedrock, due to the composition of high concentration of Ca2+ and low concentration of Mg2+. Owing to the effects of the monsoon, water chemistry was different between drought season and rainy season: the value of [Mg2+]/[Ca2+] was 0.018-0.

[Nitrate storage and transport within a typical karst aquifer system in the paralleled ridge-valley of east Sichuan].

In order to investigate the nitrate storage and transport in the karst aquifer system, the hydrochemical dynamics of Qingmuguan underground river system was monitored online by achieving high-resolution data during storm events and monthly data in normal weather. The principal component analysis was employed to analyze the karst water geochemistry. Results showed that nitrate in Jiangjia spring did not share the same source with soluble iron, manganese and aluminum, and exhibited different geochemical behaviors.

[Transportation and sources of the suspended particle in a karst spring during a storm event].

Storm periods are the crucial stage to reveal input and outlet of material and energy in groundwater system. Jiangjia spring, the outlet of Qingmuguan groundwater system, was taken as an example. Distribution of suspended particle in the Jiangjia spring was continuously monitored.

[High-resolution research on the NO3- changes of karst groundwater and its responses to the outside environmental variations].

In order to thoroughly reveal the karst groundwater system in response to the external environment, multi-index high-resolution auto-monitoring instruments were used to research the hydrogeochemistry variations of Qingmuguan subterranean stream. The monitoring indicators were pH value, electrical conductivity (EC), water level, rainfall and NO3-. In the observed 6 times rainfall events, the pH value was mainly controlled by acid rain and EC was impacted by the rain chemistry, physical dilution effect of rainfall and agricultural wastewater.

[Temporal and spatial variations of the nitrate-nitrogen sources in an underground river using 15N isotope technique].

Groundwater in Qingmuguan underground river was monitored using hydro-chemical and 15N isotope techniques to investigate temporal and spatial variations of nitrate-nitrogen and its possible sources from October, 2007 to October, 2008. The results show that nitrate concentrations are 3.20 mg/L of the inlet (D1) and 20.

[Substances transport in an underground river of typical karst watershed during storm events].

Hydrologic process, turbidity, suspended particles matters (SPM), major cations and TOC concentrations during two storm events in late April 2008 were monitored at Jiangjia Spring which is the outlet of Qingmu Guan underground river system. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) analyses of SPM were also performed in order to investigate the transport characteristics of substances, such as SPM, turbidity and major cations in the underground river of typical karst watershed. The results show that at a single and well-developed karst conduit of Jiangjia Spring, discharge, turbidity, and concentrations of SPM, major cations and TOC respond promptly to the rainfall.