春季生物作用对山地岩溶池水地球化学特征的影响

岩溶水文系统对外界环境变化敏感,使得岩溶区水质存在昼夜、小时甚至分钟等尺度的变化.许多地表水体都会经历p H值、溶解性气体、微量元素以及其他水化学指标的昼夜变化.重庆金佛山水房泉及受其补给的水池地处海拔2 050 m的山地岩溶区,具有温带气候特征.通过对水房泉泉水(以下简称泉水)及水池进行为期3 d的昼夜监测,以期探究春季生物作用对岩溶池水地球化学的影响.研究发现,在昼夜时间尺度上,泉水地球化学指标基本稳定,未表现出昼夜变化,池水地球化学指标化学表现出了昼夜波动,但水温、溶解氧、p H值、电导率等物理化学指标昼夜变化幅度较小.在不同的天气条件下,水温、溶解氧、Cl-等昼夜变化幅度存在差别;池水二氧化碳分压(p CO2)、Ca2+、DIC白天降低、晚上升高,方解石饱和指数(SIc)相反;这些指标的变化受控于温度、碳酸盐岩矿物的溶解与沉淀、水生植物光合作用与呼吸作用;通过亨利常数的计算,发现水温变化对p CO2变化的影响仅占0.79%~10.01%,水温、碳酸盐岩沉淀等物理因素对DIC损失量的贡献率为39%,水生植物光合作用的贡献率为61%.

Influences of Biological Processes on Geochemical Characteristics: An Example of a Mountain Karst Pool in Spring Season

Karst hydrologic system is quite sensitive to the surrounding environment, which leads to changes in the quality of karst water within diel,hours even minutes. Many surface water undergoes changes of pH value, dissolved gas, trace elements, nutrition and other hydrochemical parameters in a daily timescale. The Shuifang spring and its draining pool are located in Jinfo Mountain in Chongqing, the middle karst mountain belonging to temperate climate with an elevation of about 2050 m a.s.l. Diel cycles of geochemistry were measured for three days and nights to investigate the influence of biological processes on the geochemistry of the karst pool. Results showed that the geochemistry of Shuifang spring didn't exhibit diel variations, while the pool water appeared diurnal change, even if the variation amplitudes of water temperature, pH value, dissolved oxygen and specific conductance were slight. Under different weather conditions, variation amplitude of the geochemical parameters in the pool appeared discriminatory. pCO₂ and concentrations of Ca²⁺, dissolved inorganic carbon (DIC) decreased during the day time and increased in night, while calcite saturation index (SIc) showed an inverse trend. Those phenomena might be attributed to water temperature change, calcite precipitation or dissolution and the process of metabolism by the aquatic plants in the pool. It was found that the influence of water temperature change on pCO₂ accounted for only 0.79% to 10.01% by means of calculation of Henry constants. DIC loss contributed by physical factors, such as temperature and calcite precipitation, accounted for 39%, whereas the metabolism of aquatic plants accounted for 61%.