| This work was sponsored by a 2000 grant for karst dynamic system research in different areas (Grant Number 2000-164), from April 2002 to March 2003, the author collected all the data in this year through a large amount of field work, now analyzing the data and summing up the result as following:This thesis can be divided into two parts, the first part, the author wants to demonstrate the tufa-forming in the Xiangshuihe River of Xiaoqikong scenic area in Libo county, Guizhou, China; the second part, the information acquired from the tufa was used to study the paleoenvironment of Libo county.In the first part of the thesis, Methods of automatic hydrochemical logging and m-situ titrating was used to research the hydrochemistry of the river water of the Xiangshuihe River, stable carbon and oxygen isotope of the water and tufa of the river were also measured. The data show that the values of pH, water temperature and specific conductivity have a daily variation. According to the hydrochemistry data gained from different sites of the river, at the headstream of the river, the concentrations of pH and water temperature have the same variation, they have two peak values in 24 hours, one appears in the afternoon, the other at the night, the value of specific conductivity has the contrary variation; while in the downstream of theriver, the values of pH and water temperature have only one maximum in the afternoon, its specific conductivity appears minimum at the same time, according to the daily variation of the water chemistry, the values of pH and water temperature in the day are higher than at the night.Then, a seasonal variation of the water chemistry is also found both at the headstream and the downstream of the river, analyzing on the data gained during the year, in the headstream, the concentrations of pH has a minimum in the summer (about in September), on the contrary, the value of pH in the downstream is the biggest in the summer, this can be due to the different condition of the two sites: the former is in the relatively closed system and the latter in a open system.Besides the daily variation and the seasonal variation in water chemistry, the spatial variation is also one of the characteristics of water chemistry in the Xiangshuihe River. From the headstream of the river to the downstream, water samples were taken along the flow path, the pH and temperature measurements were made in situ, data show that concentrations of HCO3-, Ca2+ and specific conductivity decrease regularly along the flow path till to a minimum, then the values increase and reach another maximum, where Laya waterfall located, while the values of pH and Sic have the contrary variation comparing with the HCO3-, Ca2+ and specific conductivity.Analyses on the stable carbon isotopic composition of the tufa and the river water reflect the partial pressure of CO2 of the river water is mainly related to the karst ecological environment. The vegetation receive CO2 from the atmosphere through photosynthesis, then their roots breathe out CO2 in the soil which dissolves in water and enters the river, the stable carbon isotope of the water( 13 C) has the characteristics of both the atmosphere and the vegetation. With the conditions changing, CO2 out gassing from the water drives the river water to high degrees of supersaturation with respect to calcite, calcite precipitation occurring, the data of the stable carbon isotopic composition of the tufa-precipitation analyzed are almost the same to the result calculated in theory. The research about algae in the Xiaoqikonghad been done, which revealed that algae can increase the deposition velocity.The tufa forming of Baishuitai mentioned in the article was to strengthen the distinction of the tufa-forming in the Xiangshuihe River, for the former is the thermo-genetic while the latter is mainly related to the ecological environment.In the second part, stable carbon and oxygen isotopes of the tufa were analyzed, the age of the tufa also determined by means of carbon 14 dating, t...
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