Spatial–temporal variations of travertine deposition rates and their controlling factors in Huanglong Ravine, China – A world’s heritage site

Huanglong, well known for its unique natural travertine landscape, was listed by UNESCO as an entry in the World’s Nature Heritage in 1992, and attracts more than one million of tourists from all over the world each year. However, the landscape has undergone significant degradation (notably, serious decay of travertine) during the past two decades as the tourist numbers have increased remarkably. To understand the variations of travertine deposition rates and their controlling factors, especially the impact of tourism activities, paired water and modern travertine samples deposited on plexiglass substrates were taken along the Huanglong stream at regular intervals from early May to early November in 2010 (i.e., in the wet season). The travertine deposition rates have declined significantly compared to those in early 90s in all four subsystems in the Huanglong Ravine. The largest decrease (89.5%) occurred at the lowest sampling site. The reduction in travertine deposition most likely resulted from the phosphate pollution caused by the tourism activities. In spite of an increase in concentrations of Ca, calcite saturation, and water temperature, which facilitate calcite precipitation, deposition rates decreased because of inhibition by PO43- ions. Seasonally, three control patterns of travertine deposition rates were distinguished along the Ravine. They are control by water-temperature, control by dilution of rainwater and snow-melting water and control by PO4-inhibition of calcite precipitation.

► Travertine deposition at Huanglong decreased greatly compared to early 1990s. ► The decrease in deposition may result from the phosphate inhibition of calcite. ► It was the tourism activities that introduced more phosphate into water. ► Water-temperature and dilution showed also controls on travertine deposition.