摘要
A small spring fed stream precipitates calcite by outgassing of CO<sub>2</sub> due to chemically controlled inorganic processes. The chemical composition of the water was measured along 9 stations downstream with respect to Ca<sup>2+</sup>, Mg<sup>2+</sup>, Na<sup>+</sup>,K<sup>+</sup>, Cl<sup>-</sup>, carbonate alkalinlty, and SO<sub>4</sub><sup>2-</sup>. Temperature and pH were measured in situ. Small rectangular shaped tablets of limestone from the area were immersed into the stream for short periods and water analyses were carried out at the same time. From weight increase of the tablets, precipitation rates
A small spring fed stream precipitates calcite by outgassing of CO2 due to chemically controlled inorganic processes. The chemical composition of the water was measured along 9 stations downstream with respect to Ca2+, Mg2+, Na+,K+, Cl-, carbonate alkalinity, and SO42-. Temperature and pH were measured in situ. Small rectangular shaped tablets of limestone from the area were immersed into the stream for short periods and water analyses were carried out at the same time. From weight increase of the tablets, precipitation rates of calcite could be measured. Froe the data of the water analysis, they were compared to those calculated by the rate law of Plummer et al. (1978). The calculated rates turned out to be too high by one order of magnitude. This result is not unexpected since these calculations neglect the diffusion boundary layer between the surface of the tablets and the turbulent flowing solution, which represents a diffusive resistance. Applying a recently developed theory (Dreybrodt and Buhaann, 1991) which takes this effect into account gives a rate dependence on the thickness s of this boundary layer. The thickness a can be crudely estisated by hydrodynaaic correlations, or can be measured in situ by inserting gypsum tablets of equal shape as the limestone tablets close to the?into the strean. Since dissolution of gypsum is controlled by diffusion entirely, s can be determined from their weight loss. The theoretical calculations of calcite precipitation rates using these detemined values of s between 0.01 cm up to 0.03 ca are in good agreement with the field data. From this we conclude that a reasonable prediction of precipitation rates is possible by using Plummer's et al. rate equation and correcting it for the influence of the boundary iayer by reducing the thus obtained rates by a factor of ten.
出处
《中国岩溶》
CAS
CSCD
北大核心
1992年第S1期9-24,共16页
Carsologica Sinica
