Water- and land-borne geophysical surveys before and after the sudden water-level decrease of two large karst lakes in southern Mexico

Abstract

<jats:p>Abstract. The present geophysical study was motivated by the need to determine suitable coring locations for paleolimnological studies in two karst lakes (Metzabok and Tzibaná) of the Lacandon Forest in Chiapas, southern Mexico. We used seismic and transient electromagnetic methods to map the sediment thickness below the lake floor. When lakes were filled in March 2018, we collected seismic data with a sub-bottom profiler (SBP) and transient electromagnetic (TEM) data with a floating single-loop configuration. The latter aimed at assessing the TEM method as an alternative to seismic methods for the investigation of lake sediments and geology. After the first campaign, water levels of both studied lakes dropped dramatically by July 2019, leaving Lake Metzabok (maximum depth ~ 25 m) dry and Lake Tzibaná (~ 70 m) with a water level decreased by approx. 30 m. After the sudden drainage of the lakes, we complemented water-borne measurements by a survey carried out on the exposed lake floor in October 2019, when lake levels were still low. During this second campaign, we collected time-domain induced polarization (TDIP), and seismic refraction tomography (SRT) data on the desiccated bed of Lake Metzabok and some dry parts of Lake Tzibaná. By comparing the various data sets, we find that (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. While our results do not imply that resistivity-based methods could generally replace seismic reflection surveys for lake-bottom reconnaissance, they clearly show that TEM and TDIP surveys can provide important complementary information and resolve additional geological units or bedrock heterogeneities. </jats:p>

Evidence of large water-level variations found in deltaic sediments of a tropical deep lake in the karst mountains of the Lacandon forest, Mexico

“…Geophysical surveys at Lakes Tzibaná and Metzabok carried out in 2018 and 2019 report a strong interconnectivity between surface water and the underlying karst aquifer (Bücker et al 2021). During the field campaign in October 2019, rapid water-level variations in small remnant water bodies of Lake Metzabok (various meters within a few hours) were observed, which were clearly fed and drained through a series of crevices in the underlying limestone bedrock.…”

“…Lake Tzibaná, immersed in the Lacandon Forest (southern Mexico, 17°7′13.67″N; 91°37′39.24″W, 547 m asl; Fig. 1A), is a karst lake with a maximum depth of ~ 52 m and a surface area of ~ 1.27 km 2 during high-water stands (Bücker et al 2021). The lake has four surface hydrologic inputs (Fig.…”

“…The rocks of the region comprise dolomite and limestone deposits of uppermost Cretaceous (Maastrichtian) age in the north, and Paleogene in the south (Quezada Muñeton 1987). Lake Tzibaná lies in limestone bedrock (Bücker et al 2021) prone to develop karst features. The most important tectonic structures are NW-SE oriented faults and anticlines (SGM 2008).…”

“…The region is an important water resource for the surrounding human populations, since it hosts a large number of relatively large and deep karst lakes. However, only in recent years few lakes have been studied in more detail (Charqueño-Celis et al 2020;Bücker et al 2021;Hoppenbrock et al 2021). For instance, lakes Nahá, Amarillo, Lacandón, Metzabok and Tzibaná have been the focus of ecological and paleolimnological studies, because their sediment records have proven to represent rich archives of environmental and climatic change in the region (Domínguez-Vázquez and Islebe 2008;Díaz et al 2017).…”