New insights into the transport of sediments and microorganisms in karst groundwater by continuous monitoring of particle-size distribution
New insights into the transport of sediments and microorganisms in karst groundwater by continuous monitoring of particle-size distribution
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通过持续监测粒径分布，对岩溶地下水中沉积物和微生物的迁移有了新的认识
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发表时间：
2010
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通讯作者：
J. Zopfi
中科院分区：
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作者：
N. Goldscheider;M. Pronk;J. Zopfi
移动的颗粒对岩溶含水层中污染物的运移起着至关重要的作用，但很少有研究探讨沉积动力学与污染物之间的关系。这部分是由于监测悬浮颗粒的困难：浊度很容易测量，但不能提供颗粒大小和类型的详细信息;矿物学实验室分析很费力，不适合连续监测。便携式粒子计数器用于这里提出的研究。该仪器可提供粒度分布（PSD）的时间序列，即悬浮颗粒的数量和直径，分为0.9至139 μm的不同粒度级别。试验地点是瑞士伊韦尔东-莱斯-班斯市附近的一个岩溶系统。一个燕子洞排水农田连接到两个岩溶泉，4.8和6.3公里远，这是偶尔污染的粪便细菌在高度可变的水平。事实证明，单独的浊度并不是微生物污染的可靠指标。为了更深入地了解细菌和颗粒向泉水的迁移，进行了一项全面的研究计划，包括示踪试验和PSD，浊度，总有机碳（TOC），粪便细菌（大肠杆菌）和各种水文和物理化学参数的监测。结果表明，有两种类型的浊度：一个主要的浊度信号发生在降雨后不久，在上升的边缘的过程中，二次信号通常发生在春季流量衰退。第一个信号被解释为由于液压脉冲（原地或脉冲通过浊度）导管沉积物的再活化。第二个峰表明水从燕子洞到达，通常与TOC和粪便细菌一起（外来或流过浊度）。PSD分析表明，原生浊度是由细颗粒和大颗粒的广泛的混合物，而外来浊度主要由非常细的颗粒。这是由较大颗粒在吞孔和弹簧之间的沉降所解释的。在外来浊流期，最细颗粒（0.9-1.5 μm）与E.大肠杆菌（R2 = 0.93）。因此，细颗粒物的相对增加可以作为岩溶泉水微生物污染的“预警参数”。进一步的适用性和这种方法的局限性进行了讨论。
Mobile particles play crucial roles for contaminant transport in karst aquifers, but few studies have investigated the relationships between sediment dynamics and contaminants. This is partly due to the difficulty in monitoring suspended particles: Turbidity is easy to measure but does not deliver detailed information on the size and type of particles; mineralogical laboratory analyses are laborious and not suitable for continuous monitoring. A portable particle counter was used for the study presented here. The instrument delivers time-series of particle-size distribution (PSD), i.e. the number and diameter of suspended particles, grouped into different size-classes ranging from 0.9 to 139 μm. The test site is a karst system near the city of Yverdon-les-Bains, Switzerland. A swallow hole draining agricultural land is connected to two karst springs, 4.8 and 6.3 km away, which are occasionally contaminated by faecal bacteria at highly variable levels. Turbidity alone turned out not to be a reliable indicator for microbial contamination. To obtain more insight into bacteria and particle transport towards the springs, a comprehensive research program was carried out, including tracer tests and monitoring of PSD, turbidity, total organic carbon (TOC), faecal bacteria( E.coli ) and various hydrologic and physicochemical parameters. Results show that there are two types of turbidity: A primary turbidity signal occurs shortly after rainfall during the rising limb of the hydrograph; a secondary signal typically occurs during spring flow recession. The first signal is explained by remobilization of conduit sediments due to a hydraulic pressure pulse (autochthonous or pulse-through turbidity). The second peak indicates the arrival of water from the swallow hole, often together with TOC and faecal bacteria (allochthonous or flow-through turbidity). PSD analyses revealed that autochthonous turbidity is composed of a broad mixture of fine and large particles, while allochthonous turbidity predominantly consists of very fine particles. This is explained by sedimentation of larger particles between the swallow hole and the springs. During allochthonous turbidity periods, very good correlation between the finest particles (0.9–1.5 μm) and E. coli was found (R 2 = 0.93). The relative increase of fine particles can consequently be used as an “early-warning parameter” for microbial contamination of karst spring water. Further applicability and limitations of this approach are also discussed.