Hydrochemical variations of the Huanglong spring-fed travertine-depositing stream in the Huanglong Ravine, Sichuan, SW China, a world natural heritage site

Abstract

Huanglong Ravine belongs to the transition zone that separate the Qinghai Highland from the Sichuan Basin, Sichuan province, SW China. Travertine deposits over a width of ~ 250m for a length of 3.5 km from some springs uprive along the ravine. Methods of automatic hydrochemical logging and in-situ titrating combined with indoor analysis were used to understand the dynamic hydrochemical variations of the Huanglong Spring-fed travertine-depositing stream. The studies about the hydrochemistry of the spring-fed travertine-depositing stream are mainly focused on the spatial variation, lucubrating the travertine and discussing the characters of spatio-temporal variations and its controlling mechanism on the basis of departed analysis about spatial variations and the influence of human activities on the stream and the travertine-deposition have important meanings not only to the developing mechanism of karst, but also to the protection and exploitation of the world natural heritage site’s travertine landscape. It was found that the deposition of travertine was due to huge CO2 degassing from water, which led to the decrease in pCO2 and conductivity, and increase in pH and SIC from the Huanglong Spring to downstream. However, the downstream hydrochemical evolution was interrupted by the snow-melting water in the ravine through dilution effect, and the downstream spring waters through concentrating effect. On the other hand, the chemistry of the Huanglong Spring was stable on the diurnal scale. However, in the spring-fed pools downstream, pCO2 and EC were lower, and pH and SIC were higher in daytime than in nighttime, which shows that the deposition of travertine was quicker in daytime than in nighttime. It was found that this was caused by the combined action of higher water temperature and higher aquatic algae photosynthesis at daytime. In addition, it was found that the phosphate concentration of stream water increased remarkably downstream in the tour midseason in the Huanglong Ravine, showing the existence of water pollution by the tourism activities.