Bio-effect On Tufa Deposition

In recent years, with the development of tourism around the world, some tufa scenes, such as Huanglong-jiuzaigou Ravine, Sichuan; Huangguoshu Waterfall, Guizhou; Baishuitai, Yunnan, China and the Yellow Stone Park in the U.S., have inspired great interest of more and more people. However, the degradation of the tufa is also noticed by many people. Therefore, it is very meaningful for the administration and sustainable development of the tufa scenes to research on the formation of tufa, in order to understand its formation mechanism. In addition, there is abundant environmental information in tufa, which reflects the changes of environment, and so becomes useful in studying on the reconstructions of paleo-environment and paleo-climate.Tufa, as a product of karstification, is a carbonate sediment in pools, rivers, or springs. According to previous researches, tufa results from the supersaturation of calcium carbonate, as the partial pressure of CO₂ in the spring water is higher than that in the atmosphere and CO₂ outgases from the water. The formation of tufa is affected by many kinds of factors in the ambient environment such as temperature, water flow, and pressure, which interact and change the physical and chemical characteristics of the water leading to the degassing of CO₂ and calcium carbonate precipitation. Organism also plays an important role during the course of tufa deposition, in which aquatic plants accelerate the precipitation by photosynthesis, physiological and ecological behavior and calcification.In this paper, some experiments were done in karst water at Baishuitai,Yunnan, and Karst Experiment Site, Guilin. After monitoring the daily and seasonal changes of temperature, dissolved oxygen, pH value, and specific conductivity in the water and calculating the saturation index and partial pressure of CO₂, we try to understand the bio-effect on calcium carbonate precipitation in karst water. At the same time, we placed some pieces of glass in the flowing water at Baishuitai, Yunnan province to examine bio-effects on the rate of tufu deposition.The author got the following conclusions through almost one year in situ experiments .1. The variability of dissolved oxygen, pH value and conductivity in tufa pools and stagnant water of rivers are low during day and night if there are few aquatic plants, but if there are lots of aquatic plants, the dissolved oxygen in water increases remarkably at daytime, and reaches the highest value at two o'clock in the afternoon owing to biological effects, shows periodical changes. Generally, pH value shows synodic changes as dissolved oxygen, which is because when the intensity of photosynthesis is greater than respiration, CO₂ in water is consumed, pH value and dissolved oxygen increase. The conductivity that increases at night time, which...