川东北楼房洞洞穴系统水体元素含量季节变化与影响因素

Element contents in water collected from the Loufang Cave system in NE Sichuan, Central China: Seasonal variations and controlling factors

通过对川东北诺水河地区楼房洞洞穴系统水体Ca、Mg、Sr、Ba和U元素含量变化进行为期一年(2011年7月至2012年6月)的监测,结果发现:(1)各监测点的元素含量变化一般具有较明显的季节性,但不同的监测点之间、不同的元素之间季节变化趋势并不一致,反映了在不同的环境下不同的元素含量变化的影响机制存在差异;(2)对于2011年9月的强降水事件,河水的元素含量明显受到稀释作用影响,而洞穴内水体尤其是池水的元素含量变化明显较弱,这反映了洞穴上覆地层对外部降水事件的缓冲作用,特别是洞穴内池水由于存在更复杂的影响机制,其对外界的降水事件的响应最不敏感;(3)在所有监测点,Sr含量和Sr/Ca比值变化均表现出冬春季节相对较高而夏秋季节较低的特点,可能反映了水岩相互作用和大气沉降活动是影响Sr含量和Sr/Ca比值变化的主要机制。这对该地区岩溶洞穴沉积中的Sr含量(或Sr/Ca比值)和87Sr/86Sr比值作为研究大气粉尘活动和冬季风强度变化指标的观点给予了支持。

Monitoring of the Loufang Cave system in NE Sichuan, Central China was carried out for a period of one year lasting from July 2011 to June 2012. Concentrations of elements such as Ca, Mg, Sr, Ba, and U in stream water and pool water in the cave and in river water from outside of the cave were analyzed. Generally, concentrations of all these elements display significant seasonal variations at all monitoring sites. However, the trends of seasonal variation differentiate at different monitoring sites and between different elements, which reflects that each element may be controlled by different mechanisms. Element concentrations of river water become remarkably low during the heavy rainfall event in September 2011, obviously due to dilution effect, while those of cave waters show relatively small changes. Especially, pool water exhibits least sensitivity to this rainfall event, indicating that it is affected by complex mechanisms. These reflect the buffering effect of the epikarst overlying the Loufang Cave. Furthermore, variations of Sr concentrations and Sr/Ca ratios at all sites were relatively higher in winter and spring and lower in summer and fall, implying that the two proxies may be mainly affected by water-bedrock interaction and atmospheric dust precipitation. This observation supports previous arguments that speleothem Sr (or Sr/Ca) and 87Sr/86Sr at the study site could be used as potential indicators of atmospheric dust activity and winter monsoon variations.