Automatic hydrochemical logging and in situ titration com- bined with laboratory analysis were used to understand the spatial and temporal hydrochemical variations of the spring- fed, travertine-depositing stream in celebrated Huanglong Ravine, Sichuan, SW China. This is essential for protection of the Huanglong World Natural Heritage travertine land- scape. It was found that the deposition of travertine was due to very strong CO2 degassing from the water, leading to de- crease in pCO2 and specific conductivity (SpC), and increase in pH and SIc downstream from the Spring. However, regular downstream hydrochemical evolution was interrupted by di- lution with snow-melt water and by renewed CO2 from some downstream springs. The chemistry of Huanglong Spring itself was stable at a diurnal scale though it was altered by the great Wenchuan earthquake of May 12 2008. However, in spring-fed pools downstream, pCO2 and SpC were lower, and pH and SIc were higher in daytime than at night, which indicates that the deposition of travertine was faster during the daylight hours. This was due to the combined effects of higher water tempera- tures and higher aquatic algae photosynthesis. In addition, it was found that the phosphate concentration in the stream in- creased remarkably downstream in the tourist midseason, in- dicating water pollution by tourism activities. The increase of phosphate (an inhibitor of calcite precipitation) may be one of the reasons for the decrease in travertine deposition rates and accelerated propagation of discoloration by diatoms during the past decades, which needs to be given more comprehensive study and tackled in future for the protection of these world famous travertine deposits.
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