| During studying the global carbon cycle, we found that karst processes were important in the missing CO2 sink. CO2 from atmosphere, produced by biological activity or from deep-seated earth can dissolve in water and takes part in the action: CO2+H2O+CaCO3→Ca2++2HCO3-. At last, the karst water is abundant in HCO3- and CO2 increases biogeochemical cycle and karst development. Because the water is abundant in HCO3-, at some time calcite precipitation will take place. It has been known that many factors affect the calcite precipitation, such as temperature, CO2 pressure, hydrodynamics and biological factor. The factors lead to the CO2 outgassing from water. For example, when temperature increases, the solubility of CO2 decreases. Furthermore, the evaporation of water also decreases the solubility of CO2. Because there is a difference of CO2 pressure between water and the air, CO2 will outgas from water, when the pressure in the air becomes less. The hydrodynamic condition also affects the calcite precipitation. When water flows faster, the resistance between solid and liquid becomes less so the rate of calcite precipitation increases. When water flows much slowly, the resistance between solid and liquid becomes high. The three factors have been examined by many authors and enormous results have been achieved. However, as to the biological factor, the research is not enough. Although, some authors have studied the relationship between tufa and biological factors, they didn't give the comprehensive explanation. Zhang Chao-hui only studied the distribution and species characters of moss. Tian You-ping studied blue algae' effects on tufa, but she focus on the physical characters and the species diversity. On the other hand, Zhang Jie studied the relationship between biology and tufa on the whole. Liu et al(2001) investigated what determined the dissolution rate of calcite and found that the rate of dissolution will increase remarkably after the addition of Carbonic Anhydrase, by a factor of 10 or so at high CO2 partial pressure at lab. What will happen in the nature? Because Carbonic Anhydrase lies in the animal, plant and bacterium, we can't estimate the effect on the dissolution and precipitation of calcite and the global carbon cycle. The study is still on the primary stage. Though, some oceanographer and topographer studied the algae calcification in the sea and achieved some cheerful results, they scare studied the algae calcification in the fresh water in karst regions. So, studying the algae in the karst spring especially affected by geothermal water how to use CO2 and affect the global carbon cycle is very important for paleoenvironment reconstruction and missing CO2 sink. Through the study of the algae living in the tufa pool at Baishuitai in Yunnan province, we found there are many kinds of algae in the pool and they can live in the pool with high HCO3-. We found when pH becomes lower, HCO3- and specific conductivity increases. The result is inconsistent with our conventional thought that photosynthesis should be much higher, pH should increases and specific conductivity should decreases. This phenomena appears at noon and Martina also found similar case in German when he studied blue algae effect on tufa along two fresh streams. What leads to the phenomena? Through the physiological study of biology, we concluded it connects with the light respiration. The algae can live with little light, when the light density overcomes the limit that it can use, it will adopt respiration to protect itself instead of photosynthesis. And, CO2 produced by algae can make pH of the microenvironment decreases.By using pH-drift technology and analyzing the activity of Carbonic Anhydrase, we found that the activity of Carbonic Anhydrase on the membrane of algae was high. So , the algae uses Carbonic Anhydrase to catalyze the reaction : CO2+H2O→HCO3-+H+ for photosynthesis. At the same time, through the experiment of calcite precipitation, we found that algae through photosynthesis leads to the increase of pH and ca...
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