[Effect of Land Use on the Stability of Soil Organic Carbon in a Karst Region].

The composition of soil organic carbon and its stability mechanism are the key to understanding the terrestrial carbon sink capacity. The stability of soil organic carbon in a karst ecosystem greatly affects the soil carbon fixation capacity. In order to understand the impact of human activities on the stability of soil organic carbon in karst areas, the karst valley area of Zhongliang Mountain in Chongqing was selected as an example, and soil samples of four typical land use modes (mixed forest, bamboo forest, grassland, and cultivated land) were collected in layers to analyze the total organic carbon (TOC) and heavy fraction organic carbon (HFOC).

Tunneling-induced groundwater depletion limits long-term growth dynamics of forest trees.

Human interventions such as tunnel construction have caused groundwater depletion, which substantially affected the functions of forest tree species and their communities. However, the extent to which tunneling-induced groundwater depletion (TIGD) degrades their function levels at various spatial-temporal scales under varying climate conditions remains still unclear. Researchers used stand-scale dendrological records to track and extract the effects of TIGD associated with a single or series of tunneling events (three tunneling events during 1999-2001, 2006-2008, and 2010-2013) on short- and long-term growth levels of two dominant drought-tolerant tree species across (karst and non-karst) landscapes affected by tunnel construction and landscapes not subjected to tunnel construction in a mountainous forest ecosystem located in the southwest of China.

[Effects of Photosynthesis of Submerged Aquatic Plants on CDOM in a Karst Water System: A Case Study from Xueyu Cave, Chongqing, China].

Dissolved organic matter (DOM) in karst water is one of the most important carbon sink components, whose origins, distributions, and transport processes are of significance to carbon sink studies. Chromophoric dissolved organic matter (CDOM) can be utilized to express the composition and structural properties of DOM. In this paper, water samples were collected monthly from Xueyu Cave in a karst underground river from both inside and outside the cave.

[Distinguishing the Compositions and Sources of the Chromophoric Dissolved Organic Matter in a Typical Karst River During the Dry Season: A Case Study in Bitan River, Jinfo Mountain].

Since resistant dissolved organic matter (RDOM) plays a critically important role in a karst carbon sink, one of the most important continental carbon sinks, research focusing on the origination, transportation, and translation of RDOM in a karst water system is important. Currently, 3D-fluorescence EEMs are used to detect the composition and origination of chromophoric dissolved organic matter (CDOM), an important part of RDOM. This is a very fast and efficient method for CDOM analysis.

[Impact of Tourism on Bacterial Communities of Karst Underground River: A Case Study from Two Caves in Fengdu, Chongqing].

In this research, the bacterial community compositions of underground water in a tourist and pristine cave were studied. Xueyu Cave and Shuiming Cave are tourist and pristine caves, respectively, in the same karst cave system located in Chongqing, southwest China. To understand the impact of tourism on bacterial community compositions in underground water that flows through the caves, filtered materials from water were collected, and 16S rDNA gene sequences were obtained by high-throughput sequencing.

[Characteristics and Transport Patterns of Ammonia, Nitrites, Nitrates and Inorganic Nitrogen Flux at Epikarst Springs and a Subterranean Stream in Nanshan, Chongqing].

In a karst groundwater system, it develops complex multiple flows because of its special geological structure and unique physical patterns of aquifers. In order to investigate the characteristics and transport patterns of ammonia, nitrite and nitrate in epikarst water and subterranean stream, the water samples were collected monthly in a fast-urbanizing karst region. The results showed distinctive characteristics of three forms of inorganic nitrogen.

[Tracing the Fecal Contamination Sources Based on Bacteroides 16S rRNA PCR- DGGE in Karst Groundwater: Taking Laolongdong Underground River System, Nanshan, Chongqing as an Example].

Microbial contamination in karst groundwater continually increases and tracing the source researches has become a hot topic for international researchers. In this study, Laolongdong underground river at Nanshan, Chongqing was chosen as an example to adopt filter membrane methods to monitor the fecal microbial contaminations including the total bacterial concentration (TB), the total E. coli concentration (TE), the total fecal coliform (FC) and the total fecal Streptocoocci (FS).

[Hydrogeochemical characteristics of a typical karst groundwater system in Chongqing].

The two-year hydrologic process, hydrochemistry, and a portion of deltaD, delta18O of both the surface water at the inlet and the groundwater at the outlet, were investigated to identify the spatial and temporal variations of hydrogeochemistry in the Qingmuguan karst groundwater system. Research results show that there are wet and dry periods in the groundwater system owing to the striking influence of seasonal rainfall. The evolution of the chemical compositions in the groundwater is significantly influenced by the water and rock interaction, anthropogenic activities and rainwater dilution.

[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.