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

Abstract

The karst lakes in Jiuzhaigou Nature Reserve are an integral part of the karst lake landscape, yet research on the formation mechanism for the color of the blue-green lakes in Jiuzhaigou is insufficient. With the help of hyperspectral instruments, coupled with hydro-chemical analysis, this paper elaborates on the unique color characteristics of the Jiuzhaigou karst lakes, delves into the color formation mechanism of the lakes, establishes a regression equation for the color of the lakes as well as the water quality parameters, and sheds light upon the causes for the color distinction between the karst lakes in Jiuzhaigou and the plateau freshwater lakes. The experiment shows that the Jiuzhaigou karst lakes are primarily blue and green, while the proportion of short-wavelength light in the normalized water-leaving radiance and the total incident irradiance of lake water is higher. Based on the redundancy analysis and the correlation analysis, travertine deposition is the core link in the color formation of the blue karst lakes in Jiuzhaigou, while the selective reflection and scattering of the suspended calcium carbonate particulate matters towards visible light represents the optical foundation for the formation. In addition, physical factors such as depth and transparency, changes to the water quality parameters that affect the travertine deposition rate, and the eutrophication process will all exert significant influence over the formation. By building on water-leaving radiance, this paper quantifies the lake color with the tristimulus values (R, G, B) via colorimetrical methods, which features solid goodness of fit with the linear regression equation established based on the water quality parameters. The principal component analysis and colorimetrical analysis show that the color of the karst lakes in Jiuzhaigou varies substantially from that of the plateau freshwater lakes, which mainly results from the difference in the water quality. Research conducted in this paper on the color formation mechanism of the distinct blue karst lakes in Jiuzhaigou illuminates the formation and maintenance mechanism of the plateau karst lakes, which is conducive to better understanding towards the relationship between the water quality and colors of the karst lakes, and provides scientific proof for the establishment of the water quality assessment indicator system based on the colors of the karst lakes.

New species of the genus Molanna Curtis, 1834 (Trichoptera, Molannidae) in China inferred from morphology and DNA barcodes

“…The Reserve is an example of typical karst geology, with a high amount of travertine calcite deposits in freshwater habitats ( Wang et al 2018 ). The majority of the lakes are oligotrophic, with low concentrations of total suspended solids and low turbidity ( Li et al 2020 ). Water temperature is relatively low in the lakes, whereas conductivity, alkalinity, and pH are relatively high ( Cao et al 2016 ).…”

Susceptibility Mapping of Unhealthy Trees in Jiuzhaigou Valley Biosphere Reserve

“…The reserve boasts not only stunning landscapes, including waterfalls, calcifications, and terraces, but also hosts a diverse array of rare and protected species, making it a crucial animal and plant gene bank [38,39]. The topography of Jiuzhaigou Valley is characterized by rolling peaks, with elevations ranging from 1996 m at the entrance to 4764 m at the highest point [40]. Jiuzhaigou Valley boasts an impressive 80% vegetation cover, displaying a vertical distribution pattern [41].…”

Modeling the Relationships between the Height and Spectrum of Submerged Tufa Barrage Using UAV-Derived Geometric Bathymetry and Digital Orthoimages

“…On the other hand, a large number of optically significant components such as suspended matter, chlorophyll, and colored dissolved organic matter combine to determine the inherent optical properties of the submerged tufa barrage [47]. For instance, selective absorption of the blue band by planktonic algae will change the lake color into green or red [50]. Therefore, the relationship between the height and spectrum of the submerged tufa barrage is actually a dynamic process.…”