Integrated land and water-borne geophysical surveys shed light on the sudden drying of large karst lakes in southern Mexico
Integrated land and water-borne geophysical surveys shed light on the sudden drying of large karst lakes in southern Mexico
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DOI：
10.5194/se-12-439-2021
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发表时间：
2021-02-24
期刊：
影响因子：
3.4
通讯作者：
Perez, Liseth
中科院分区：
文献类型：
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作者：
Buecker, Matthias;Orozco, Adrian Flores;Perez, Liseth
岩溶水资源在饮用水供应方面发挥着重要作用，但即使是轻微的气候变化也极易造成影响。因此，需要坚实的和空间密集的地质信息来模拟岩溶水文系统对这种变化的响应。此外，湖泊沉积物中的环境信息可用于了解过去气候对岩溶水系统的影响。在本研究中，我们进行了多方法的地球物理调查，调查地质情况和沉积填充的两个岩溶湖（Metzabok和Tzibana）的Lacandon森林恰帕斯州，墨西哥南部。这两个湖泊都呈现出巨大的季节性湖面波动，并在2019年上半年经历了异常突然和强烈的湖面下降，导致Metzabok湖（最大深度约为25米）完全干涸，Tziband湖（深度约为70米）水位下降约1.5米。15米。在此事件之前，在2018年3月的湖平面高位期间，我们使用浅地层剖面仪（SBP）收集了水上地震数据，并使用新开发的浮动单回路配置收集了瞬变电磁（TEM）数据。2019年10月，在突发排水事件发生后，我们利用这一独特的情况，直接在Metzabok湖和Tziband湖的裸露湖底进行了补充测量。在第二次活动中，我们收集了时域激发极化（TDIP）和地震折射层析成像（SRT）数据。通过整合多种方法的数据集，我们（1）确定了两个湖泊底部5-6 m厚、可能未受干扰的沉积物序列，这些序列适合未来的古环境钻探活动，（2）开发了一个综合地质模型，表明地表水和岩溶含水层之间有很强的相互联系，（3）评价应用地球物理方法普查岩溶湖泊地质情况的潜力。这种方法评价表明，在给定的情况下，（i）SBP和TDIP相位图像一致地解决了覆盖湖底的细粒湖相沉积物的厚度，（ii）TEM和TDIP电阻率图像一致地检测石灰岩基岩的上限和河流三角洲河流沉积物的几何形状，和（iii）TDIP和SRT图像表明存在一个层，该层将湖相沉积物与石灰岩基岩分开，并由崩塌碎屑与湖相沉积物混合组成。我们的研究结果表明，结合地震方法，这是最广泛用于湖底普查，与基于连续性的方法，如TEM和TDIP可以显着提高解释，解决地质单元或基岩非均质性，这是不可见的地震数据。只有使用补充方法才能提供足够的信息来开发这种复杂岩溶环境的综合地质模型
Karst water resources play an important role in drinking water supply but are highly vulnerable to even slight changes in climate. Thus, solid and spatially dense geological information is needed to model the response of karst hydrological systems to such changes. Additionally, environmental information archived in lake sediments can be used to understand past climate effects on karst water systems. In the present study, we carry out a multi-methodological geophysical survey to investigate the geological situation and sedimentary infill of two karst lakes (Metzabok and Tzibana) of the Lacandon Forest in Chiapas, southern Mexico. Both lakes present large seasonal lake-level fluctuations and experienced an unusually sudden and strong lake-level decline in the first half of 2019, leaving Lake Metzabok (maximum depth similar to 25 m) completely dry and Lake Tziband (depth similar to 70 m) with a water level decreased by approx. 15 m. Before this event, during a lake-level high stand in March 2018, we collected water-borne seismic data with a sub-bottom profiler (SBP) and transient electromagnetic (TEM) data with a newly developed floating single-loop configuration. In October 2019, after the sudden drainage event, we took advantage of this unique situation and carried out complementary measurements directly on the exposed lake floor of Lakes Metzabok and Tziband. During this second campaign, we collected time-domain induced polarization (TDIP) and seismic refraction tomography (SRT) data. By integrating the multi-methodological data set, we (1) identify 5-6 m thick, likely undisturbed sediment sequences on the bottom of both lakes, which are suitable for future paleoenvironmental drilling campaigns, (2) develop a comprehensive geological model implying a strong interconnectivity between surface water and karst aquifer, and (3) evaluate the potential of the applied geophysical approach for the reconnaissance of the geological situation of karst lakes. This methodological evaluation reveals that under the given circumstances, (i) SBP and TDIP phase images consistently resolve the thickness of the fine-grained lacustrine sediments covering the lake floor, (ii) TEM and TDIP resistivity images consistently detect the upper limit of the limestone bedrock and the geometry of fluvial deposits of a river delta, and (iii) TDIP and SRT images suggest the existence of a layer that separates the lacustrine sediments from the limestone bedrock and consists of collapse debris mixed with lacustrine sediments. Our results show that the combination of seismic methods, which are most widely used for lake-bottom reconnaissance, with resistivity-based methods such as TEM and TDIP can significantly improve the interpretation by resolving geological units or bedrock heterogeneities, which are not visible from seismic data. Only the use of complementary methods provides sufficient information to develop comprehensive geological models of such complex karst environments