Factors Affecting Tufa Degradation in Jiuzhaigou National Nature Reserve, Sichuan, China

Abstract

Water and tufa samples were collected from Arrow Bamboo Lake, the stream from Panda Lake to Five-Color Lake, Pearl Shoal and Shuzheng Lakes in Jiuzhaigou National Nature Reserve, China, between October 2013 and September 2014, to investigate tufa growth rate and water environment (water temperature, pH, electric conductivity, major ions and nutrients), and analyzed to explore the main causes of tufa degradation. The mean annual rate of tufa growth was low and varied within lakes, with the maximum deposit thickness of 332 µm/y. The calcite saturation index ranged from 0.65 to 0.83. Scanning electron microscope images showed that the tufa deposits had non-isopachous structures, and diatoms were the dominant microorganisms that participated in tufa deposition. Porous and crystalline structures of deposits were linked with a high tufa growth and small amounts of diatoms. Conversely, tufa deposits with amorphous and loose structures showed a low crystal growth rate and a high number of diatoms. A one-way analysis of variance and a least significant difference test were applied to identify site differences in water chemistry. Linear correlations indicated that nitrate, phosphate and sulfate inhibit tufa growth (p < 0.05). Increased nitrogen and phosphorus concentrations that originate mainly from atmospheric pollution and tourist activities at scenic attractions could trigger excessive diatom growth, which inhibits tufa precipitation. A series of measures should be implemented (e.g., the visitor number and vehicles should be regulated and controlled) to minimize tufa degradation in the Jiuzhaigou National Nature Reserve.

Calcerous Tufa as Invaluable Geotopes Endangered by (Over-)Tourism: A Case Study in the UNESCO Global Geopark Swabian Alb, Germany

“…Our surveys are consistent with observations from other national and international geoparks. Here, too, high-quality tufa landforms are attraction factors for high visitor numbers [26][27][28] but are also subject to increasing degradation and endangerment as a result [15][16][17]54,[62][63][64][65][66][67][68]. This is due to the high vulnerability of the Tufa landforms, particularly cascades and sinter basins [62,63].…”

“…Calcerous tufa and sinter are among the most impressive natural spectacles in karst landscapes, whose scientific and aesthetic values are universally recognized [15][16][17][18][19][20][21][22][23][24][25]. They, therefore, attract a growing number of visitors [26][27][28] but are unfortunately extremely vulnerable and can be seriously damaged even by minor inference. The rediscovery of the "Heimat" (homeland), associated with a significant increase in visitors to natural areas led to negative repercussions for the environment [40].…”

“…Jiuzhaigou National Nature Reserve and the scenic and historic region of Huanglong are popular tourist destinations in China. The number of tourists in Jiuzhaigou has increased from 27,000 in 1984 to 5.1 million in 2015, which represents a 188-fold increase [28]. In the light of the negative impact of such tourist crowds on the environment, this explosion of visitor numbers may be classified as 'overtourism' [29].…”

The Color Formation Mechanism of the Blue Karst Lakes in Jiuzhaigou Nature Reserve, Sichuan, China

“…Water in the valleys mainly comes from precipitation, mountain meltwater and underground karst water. Travertine is a type of calcium carbonate deposit [38] and also an important part of the landscape in Jiuzhaigou. Primarily distributed in the Rize Valley, the Shuzheng Valley and their branches, it stretches for around 30 km intermittently and covers 2.44 km 2 .…”

“…Research has found that sulphate can slow down the nucleation crystallization of calcium carbonate and alter the crystal shapes as well as surface property. When concentrations of sulphate and nitrate in the solution lower, the calcite saturation index (SI C ) rises, contributing to the deposition process [38,70,71]. Except for inorganic ions, it is generally believed that dissolved organic matter (DOM) or dissolved organic carbon (DOC) is essential to travertine deposition.…”