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The Changjiang River is the largest freshwater river in China. Here, the sources and variability in nitrate of the Changjiang River are assessed for the first time using dual isotopic approach. Water samples were collected once in August 2006 from the main channel of the Changjiang and its major tributaries. The concentrations and isotopic composition of nitrate were then analyzed for the waters in the Changjiang River. The δ15N and δ18O of NO3- ranges from 7.3‰ to 12.9‰ and 2.4‰ to 11.2‰ in the Changjiang River waters, respectively. The ranges of isotopic compositions of nitrate suggested that nitrification (including "modified fertilizer") and urban sewage effluent are the major sources of nitrate in the Changjiang River. The high δ18O-NO3- values were observed in the water of the upper reaches, indicated that the current drought might be one important reason for shifting of isotopes in the special sampling period. In addition, there was a strong positive relationship between δ15N-NO3- and δ18O-NO3-, which indicated that denitrification added to the enrichment of heavy isotopes of nitrate. [ABSTRACT FROM AUTHOR]

Because of active exchange between surface and groundwater of a karstic hydrological system, the groundwater of Guiyang, the capital city of Guizhou Province, southwest China, has been seriously polluted by anthropogenic inputs of NO3-, SO42-, CI-, and Na+. In this work, δ37CI of chloride and δ34S variations of sulfate in the karstic surface/groundwater system were studied, with a main focus to identify contaminant sources, including their origins. The surface, ground, rain, and sewage water studied showed variable δ37CI and δ34S values, in the range of -4.1 to +2.0%‰ and -20.4 to +20.9‰ for δ37CI and δ34S (SO42-), respectively. The rainwater samples yielded the lowest δ37CI values among those observed to date for aerosols and rainwater. Chloride in the Guiyang area rain waters emanated from anthropogenic sources rather than being of marine origin, probably derived from HCI (g) emitted by coal combustion. By plotting 1/SO42- vs δ34S and 1/Cl- vs δ37CI, respectively, we were able to identify some clusters of data, which were assigned as atmospheric deposition (acid rain component), discharge from municipal sewage, paleo-brine components in clastic sedimentary rocks, dissolution of gypsum mainly in dolomite, oxidation of sulfide minerals in coal-containing clastic rocks, and possibly degradation of chlorine-containing organic matter We conclude that human activities give a significant input of sulfate and chloride ions, as well as other contaminants, into the studied groundwater system through enhanced atmospheric deposition and municipal sewage, and that multiple isotopic tracers constitute a powerful tool to ascertain geochemical characteristics and origin of complex contaminants in groundwater. [ABSTRACT FROM AUTHOR]

Nitrate pollution of the karstic groundwater is an increasingly serious problem with the development of Guiyang, the capital city of Guizhou Province, southwest China. The higher content of NO3- in groundwater compared to surface water during both summer and winter seasons indicates that the karstic groundwater system cannot easily recover once contaminated with nitrate. In order to assess the sources and conversion of nitrate in the groundwater of Guiyang, we analyzed the major ions, δ15N-NH4+, δ15N-NO3-, and δ18O-NO3- in surface and groundwater samples collected during both summer and winter seasons. The results show that nitrate is the major dominant species of nitrogen in most water samples and there is a big variation of nitrate sources in groundwater between winter and summer season, due to fast response of groundwater to rain or surface water in the karst area. Combined with information on NO3-/CI-, the variations of the isotope values of nitrate in the groundwater show a mixing process of multiple sources of nitrate, especially in the summer season. Chemical fertilizer and nitrification of nitrogen-containing organic materials contribute nitrate to suburban groundwater, while the sewage effluents and denitrification mainly control the nitrate distribution in urban groundwater. [ABSTRACT FROM AUTHOR]

Variations in the concentrations and isotopic compositions (δ13CDIC) of dissolved inorganic carbon (DIC) reflect contamination and biogeochemical cycling of the carbon in ground water. In order to understand contamination and biogeochemical cycling of DIC, we carried out research on the geochemistry of ground water of Guiyang, the capital city of Guizhou Province, China. Results show that ground water is mainly characterized by SO₄·HCO₃-Ca·Mg and HCO₃-Ca·Mg chemical compositions. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquifers. HCO₃- is the dominant species of DIC in ground water and has lower concentrations and more negative values of δ13CDIC in the high-flow (summer monsoon) season, as compared to the low-flow season. This indicates that DIC is relatively enriched in carbon of biological origin in the high-flow season as compared to the low-flow season and that biological activities are the predominant control on shifts of stable carbon isotope values. The evidence that the δ13CDIC values of ground water decrease with increasing concentrations of anthropogenic species shows that the carbon isotopic composition of DIC can be a useful tracer of contamination, in addition to biogeochemical cycling of inorganic carbon in ground water. Results from this study show that ground water is impacted by significant levels of contamination from human activities, especially in the urban areas, as well as the northeast and west suburbs, in Guiyang city, southwest China. [ABSTRACT FROM AUTHOR]

The Dongguashan skarn copper deposit can be considered as the product of the transport‐chemical reaction coupling process of ore‐forming materials (for example, complexes of copper) in discrete, parallel fractures in a porous medium system. A mathematical model of metallogenesis has been established and the accurate analytical solutions for depicting the transport of ore‐forming materials have been worked out. In establishing the model of metallogenesis and working out the analytical solutions, the following aspects have been taken into consideration: (1) advective transport along fractures; (2) diffusion and longitudinal mechanical dispersion of ore‐forming materials (solutes) along the fracture axis; (3) diffusion of ore‐forming materials from the fractures to the wall media; (4) adsorption of ore‐forming materials on the surface of wall‐rock matrices; (5) adsorption of ore‐forming materials within the wall‐rock matrices; (6) reduction of the concentrations of solutes due to the chemical reactions between ore fluids and wall‐rock matrices and the precipitation of ore‐forming materials. [ABSTRACT FROM PUBLISHER]

The authors discuss aspects of ocean acidification due to the production of carbonic acid with the dissolution of the increasing atmospheric carbon dioxide. They cite the impact of the reduction of carbonate minerals to the dynamics, structure and biodiversity of coral reefs and other marine organisms. The authors mention the importance of complete charge balance for both chemical and biological processes.

Moss N isotope (δ15Nbulk) has been used to monitor N deposition, but it remains questionable whether inhibition of nitrate reductase activity (NRA) by reduced dissolved N (RDN) engenders overestimation of RDN in deposition when using moss δ15Nbulk. We tested this question by investigation of δ15Nbulk and δ15Nbulk- in mosses under the dominance of RDN in N depositions of Guiyang, SW China. The δ15Nbulk of mosses on bare rock (-7.9‰) was unable to integrate total dissolved N (TDN) (δ15N = -6.3‰), but it reflected δ15N-RDN (-7.5‰) exactly. Moreover, δ15N-NO3- in mosses (-1.7‰) resembled that of wet deposition (-1.9‰). These isotopic approximations, together with low isotopic enrichment with moss [NO3-] variations, suggest the inhibition of moss NRA by RDN. Moreover, isotopic mixing modeling indicated a negligible contribution from NO3- to moss δ15Nbulk when the RDN/NO3- reaches 3.8, at which maximum overestimation (21%) of RDN in N deposition can be generated using moss δ15Nbulk as δ15N-TDN. Moss δ15N-NO3- can indicate atmospheric NO3- under distinctly high RDN/NO3- in deposition, although moss δ15Nbulk can reflect only the RDN therein. These results reveal pitfalls and new mechanisms associated with moss isotope monitoring of N deposition and underscore the importance of biotic N dynamics in biomonitoring studies. [ABSTRACT FROM AUTHOR]

Nanming River, the largest urban river in Guizhou Province, southwestern China plateau, has been severely polluted for decades. This study characterizes the organic materials and their sources in the upstream and downstream waters by dissolved organic carbon (DOC), excitation emission matrix (EEM) spectroscopy, parallel factor (PARAFAC) analysis and photo-microbial experiments. DOC concentrations were low (47–120 μM C) upstream and relatively high (146–462 μM C) downstream. The PARAFAC studies on the sample EEM spectra demonstrated that the upstream dissolved organic matter (DOM) was mostly composed of one component that had a fulvic acid-like substance; downstream DOM was composed of two components with mixtures of tryptophan-like and fulvic acid-like substances. From the results of the sewerage drainage samples collected along the bank of the river, it is evident that both household detergent-like and protein-like or tryptophan-like substances are predominantly present, indicating that untreated sewerage effluents are the major sources of organic matter pollution in Nanming River. The degradation experiments conducted on river, sewerage drainage and commercial detergent samples demonstrated that the detergent-like and tryptophan-like substances are both photochemically and microbiologically more decomposable than fulvic acid-like materials under sunlight and dark incubations. These results suggest that the input of the untreated sewerage effluents along the streams is the major pollution source in Nanming River, and the fluorescent DOM was efficiently affected by both photochemical and microbial processes. [ABSTRACT FROM AUTHOR]

Secular variations in the carbon isotopic composition of organic and carbonate carbon characterize the Lower to Middle Cambrian transition that is exposed on the Yangtze Platform at Taijiang, Guizhou Province, southern China. δ13C values for organic matter range between -33.4 and -26.5‰. The carbon isotopic composition for carbonate carbon fluctuates between -2.7 and +3.1‰. A progressive decrease in the isotopic difference (Δδ) between these two isotope records reflects a decrease in the proportional contribution of bacterial biomass to the total sedimentary organic matter. In general, the observed changes are interpreted to reflect primary depositional values, notably variations in the burial rates of organic matter. These, in turn, are linked to biological changes across the Lower to Middle Cambrian transition. No distinct shift in the carbon isotopic composition marks the proposed Lower--Middle Cambrian boundary. [ABSTRACT FROM AUTHOR]

Plant nitrogen (N) use is a key component of the N cycle in terrestrial ecosystems. The supply of N to plants affects community species composition and ecosystem processes such as photosynthesis and carbon (C) accumulation. However, the availabilities and relative importance of different N forms to plants are not well understood. While nitrate (NO3-) is a major N form used by plants worldwide, it is discounted as a N source for Arctic tundra plants because of extremely low NO3- concentrations in Arctic tundra soils, undetectable soil nitrification, and plant-tissue NO3- that is typically below detection limits. Here we reexamine NO3- use by tundra plants using a sensitive denitrifier method to analyze plant-tissue NO3-. Soil-derived NO3- was detected in tundra plant tissues, and tundra plants took up soil NO3- at comparable rates to plants from relatively NO3--rich ecosystems in other biomes. Nitrate assimilation determined by 15N enrichments of leaf NO3- relative to soil NO3- accounted for 4 to 52% (as estimated by a Bayesian isotope-mixing model) of species-specific total leaf N of Alaskan tundra plants. Our finding that in situ soil NO3- availability for tundra plants is high has important implications for Arctic ecosystems, not only in determining species compositions, but also in determining the loss of N from soils via leaching and denitrification. Plant N uptake and soil N losses can strongly influence C uptake and accumulation in tundra soils. Accordingly, this evidence of NO3- availability in tundra soils is crucial for predicting C storage in tundra. [ABSTRACT FROM AUTHOR]

Total carbon content of the atmospheric suspended particulate matters consisted of as high as 89-93% organic carbon (OC) in Ulaanbaatar aerosol without showing seasonal variation. However, limited aerosol measurements have been conducted on these OC rich aerosols particularly for high molecular weight constituents. In order to address the gap above, abundance of high molecular weight humic-like substances (HULIS) in total suspended particulates (TSP) from Ulaanbaatar atmospheric aerosol were determined for the first time. HULIS molecular structure was characterised for different seasons using carbon content and UV absorbance measurements coupled with solid phase extraction methods. Although, HULIS contributions to water soluble organic fraction of the winter and summer aerosols were similar HULIS carbon concentration was higher in winter samples (9-37 mg·L-1) than in summer (2-6 mg·L-1). Consequently quantity of aromatic moieties and degree of aromaticity varied between seasons. [ABSTRACT FROM AUTHOR]

Pseudosections for two sediments and one basalt calculated in the system K2O–Na2O–CaO–MgO–FeO–Fe2O3–Al2O3–TiO2–SiO2–H2O for the P–T range 10 to 35 kbar, 300 to 900°C give useful insights into the amount of H2O released from oceanic crust in subduction zones. In cold subduction zones (20 kbar–300°C to 35 kbar–500°C) hydrous minerals storing 3 to 4 wt% H2O are still present in metasediments at depths of 120 km. In the same environment, metabasite releases 1 wt% H2O in the depth range 100 to 120 km, but 4.5 wt% H2O is transported to greater depths. In hot subduction zones (300°C hotter than the cold subduction zone at 100 km depth), dehydration events of metasediments in the depth range 50 to 80 km correspond to the breakdown of chlorite and paragonite. In the calculations no further water is released at greater depths because the modal content of phengite, the only hydrous mineral phase at these depths, remains almost constant. For the same P–T path, metabasite shows continuous dehydration between 40 and 80 km releasing almost 3 wt% H2O. At 120 km depth less than 0.4 wt% of H2O remains. In an average modern subduction zone (∼6°C/km) most dehydration of sediments occurs at depths of 70 to 100 km and that of basalts at depths of 80 to 120 km. Only 1.3 wt% H2O in metasediments and 1.6 wt% H2O in metabasalt has the potential to be subducted to depths greater than 120 km. The dehydration behavior of sediments concurs with the generally held idea that subduction zone fluids are most effectively transported to great depths by cold subduction. In hot subduction zones, such as those characteristic of early Earth, most H2O carried by oceanic crust is liberated at depths less than 120 km and, thus, would not contribute to island-arc magmatism. [ABSTRACT FROM AUTHOR]