Search

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]

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.