Influence Mechanism of Chlorella vulgaris on the Process of Travertine Deposition under Different Ca2+ Concentration

Travertine, a famous karst carbonate precipitate, undergoes formation influenced by the biological activities of microorganisms such as algae. Elucidating the role of biodeposition in travertine formation will contribute to a better understanding of the microstructure of travertine. This study focuses on the effects of Chlorella vulgaris on the deposition process of travertine under laboratory conditions. Through comprehensive analyses of physical and chemical parameters, phase structure, crystal morphology, and microbial communities in the aquatic environment, the findings demonstrated that the increase in Ca2+ concentration has a deleterious effect on the growth of Chlorella vulgaris, leading to a reduction in calcification rate. The highest rate of calcification was observed when the concentration of Ca2+ reached 200.98 mg/L. As the concentration of Ca2+ increased, the maturation of calcification crystals was enhanced, leading to a more distinct outline of these crystals. Chlorella vulgaris facilitates the crystallization of calcium carbonate by offering nucleation sites and templates for growth, thereby markedly enhancing the deposition process of travertine. At a moderate concentration of calcium (c(Ca2+) = 200.98 mg/L), an increase in the population of Enterobacteriales (Beneficial bacteria of travertine deposition) and a reduction in the proportion of Pseudomonadales (Harmful bacteria deposited by travertine) were observed, resulting in an enhanced capacity for Chlorella vulgaris to deposit travertine. The present study elucidates the underlying mechanisms by which Chlorella vulgaris facilitates travertine formation, thereby establishing a robust scientific foundation for the ecological protection of travertine landscapes.