云南白水台钙华水池中水化学日变化及其生物控制的发现

Diurnal variations in hydrochemistry in a travertine-depositing stream at Baishuitai,Yunnan,SW China: Observations and Explanations

为弄清云南白水台泉及其下游钙华水池中水化学的日变化,选取1号泉及其流经的两个钙华水池(6号和10号)作为研究对象并对其水温、pH值和电导率进行了自动监测。根据Ca2+、HCO3-与电导率存在的线性关系,用WATSPAC软件计算了水中方解石的饱和指数和PCO2。监测发现:泉水不存在显著的水化学日动态变化,而两个钙华水池表现出显著的日动态变化。其中10号钙华水池在白天温度较高时水中的CO2大量逸出并通过水下水生植物的光合作用加速了水中碳酸钙的沉积。6号钙华水池水生植物生长茂盛,其叶片和部分枝干露出水面,因而光合作用主要发生在空中,所以此处水化学表现为白天pH值降低和电导率升高的反常现象,即由温度主导的根呼吸作用,在白天释放更多的CO2进入水体而使沉积下来的碳酸钙重新溶解。

Diurnal variations in hydrochemistry were monitored at a spring and two pools in a travertinedepositing stream at Baishuitai, Yunnan, SW China. Water temperature, pH and specific conductivity were measured in intervals of 5 and 30 minutes for periods of 1 to 2 days. From these data the concentrations of Ca^2＋ , HCO3^- , calcite saturation index, and CO2 partial pressure were derived. The measurements in the spring of the stream did not show any diurnal variations in the chemical composition of the water. Diurnal variations, however, were observed in the water of the two travertine pools downstream. In one of them rise in temperature （thus more CO2 degassing） during day time and consumption of CO2 due to photosynthesis of submerged aquatic plants accelerated the deposition of calcite, whereas in the other pool, where aquatic plants flourished and grew out of the water （so photosynthesis were taking place in the atmosphere）, obervations suggest that temperaturedependent root respiration underwater took place, which dominated until noon. Consequently, due to the release of CO2 by the root respiration into water, which dominated CO2 production by degassing induced by temperature increase, the increased dissolution of calcite was observed. This is the first time anywhere that the effect of root respiration on the diurnal hydrochemical variations has been observed. Given that the temperature of the Baishuitai stream waters is a function of insolation, changes in the travertine deposition downstream under the base flow conditions are a direct function of the prevailing weather. This has implications for the paleoclimatic interpretation of fossil travertine deposits. Fossil travertine may also provide information on growth status of the paleo-aquatic plants, which could complicate the paleo-environmental interpretation.