Spatial and seasonal variations of trace metals in a karst water system in Central China and implications

Based on monitoring (2011.7-2012.6) of a karst water system in NE Sichuan, Central China, we presented monitoring results of the spatial and seasonal variations of metals Ca, Mg, Sr and Ba in cave waters and surface river water. Three sites were chosen for the monitoring. SLPB and LZLY are two in-cave sites and HS represents the Nuoshui River. SLPB is the deepest point of the cave, where an underground river emerges. There is fast dripping water in winter and the drip water becomes a waterfall in summer. LZLY is the pool. The drip water at SLPB, pool water at LZLY and surface river water at HS were collected once a month from July 2011 to June 2012. At each site, about 500 ml of waters were sampled with pre-cleaned polypropylene bottles (Nalgene), acidified in site to pH<2 with double distilled HNO3. These samples were kept in a refrigerator at a low temperature (~ 4°C) until analysis. On average, the surface river water represented by HS experienced much less water-rock interaction compared with the cave waters at SLPB and LZLY, providing us the opportunity to investigate the influence of water-rock interaction on the hydro-geochemistry of groundwater enroute to Loufang Cave. Ca, Mg, Sr, and Ba in these water samples were measured at the geochemistry laboratory of Southwest University in China. Mg and Ca were analyzed with an ICP-OES with detection limits of 1×10-9 and analytical precisions (RSD) better than 1%. Sr and Ba were analyzed with an ICP-MS with RSD better than 5%. A synthetic multi-element standard (High-Purity Standards) was used for external calibration.

本数据集基于中国华中地区川东北某岩溶水系统2011年7月至2012年6月的原位监测工作，呈现了洞穴水体与地表河水中Ca、Mg、Sr及Ba等金属元素的空间分布与季节变化特征的监测结果。本次监测共选取3个采样点位：SLPB与LZLY为两处洞内点位，HS代表诺水河地表水体。SLPB为该洞穴的最深点位，此处有地下河出露；冬季滴水流速较快，夏季滴水可形成瀑布景观。LZLY为一处水池点位。2011年7月至2012年6月期间，每月采集一次SLPB处的滴水、LZLY处的池水以及HS处的地表河水样品。每个点位均采用预先清洗后的聚丙烯（Nalgene）采样瓶采集约500mL水样，现场使用双蒸馏硝酸将水样酸化至pH<2。采集后的样品置于约4℃的低温冰箱中保存，直至开展分析测试。整体而言，以HS代表的地表河水相较于SLPB与LZLY处的洞穴水体，其水-岩相互作用程度显著更弱，这为探究水-岩相互作用对径流至娄坊洞的地下水水文地球化学特征的影响提供了研究契机。本次研究中所有水样的Ca、Mg、Sr及Ba元素含量均在中国西南大学地球化学实验室完成测定：其中Mg与Ca采用电感耦合等离子体发射光谱仪（ICP-OES）进行分析，检测限为1×10^-9，分析精密度（相对标准偏差RSD）优于1%；Sr与Ba则采用电感耦合等离子体质谱仪（ICP-MS）进行分析，相对标准偏差优于5%。分析过程采用High-Purity Standards生产的合成多元素标准物质进行外标校准。