Sudden drying of large karst lakes in the Lacandon Maya region of southern Mexico

点击翻译按钮获取中文摘要

Lacandones, native Lacandon Maya inhabitants, observed that lake levels from Lakes Metzabok and Tzibaná, two of the largest karst lakes in the Lacandon Forest in southern Mexico, declined dramatically within a two-week period in July 2019. Lake Metzabok (0.83 km2; Zmax = 25 m) dried completely, whereas Lake Tzibaná (1.24 km2; Zmax = 70 m) experienced a level decline of about 30 m. Most karst lakes in the region have good water quality, and are important natural water reservoirs for humans as well as habitats for aquatic and terrestrial organisms. Desiccation of aquatic ecosystems has profound ecological and environmental effects causing biodiversity and genetic diversity loss. As geoscientists, we see this as a once-in-a-lifetime opportunity to study in great detail the effects of this dramatic environmental event and to use these results as “modern analogues” for past episodes of drying in the environmental record. Therefore, the overall objective of the proposed multi-disciplinary project is to conduct a 2-week-field campaign to evaluate the hydrological and ecological effects of the sudden drying of Lakes Metzabok and Tzibaná using neo- and paleolimnological, geophysical, and geological analysis. Our priority is to study the chemical composition of the water column and surface sediments in remnant water bodies and capture how evidence for such drying events is preserved in lake sediments. The evolution of the recent desiccation event will be inferred by a high-resolution multi-proxy analysis from the upper-most centimeters of short cores, and comparison with meteorological data for the region. Finally, we will gather information of sensitivities and tolerances of living aquatic and terrestrial species, and the magnitude of ecological changes. The hydrology of karst lakes is complex and unpredictable because multiple geological and hydrological factors control the water balance. Geophysical and basic geological surveys will provide important insights into possible mechanisms that lead to sudden desiccation. Geophysical survey methods will enable us to obtain information on the geometry and thickness of the lacustrine sediments in both lakes, important information for future paleolimnological and paleoclimatic studies. In addition, comparison of survey data from 2018, when the lakes were filled, with data to be collected directly from the desiccated lake floor, presents a rare and valuable opportunity to calibrate water-borne geoelectrical and electromagnetic methods for sediment characterization. The proposed project will generate valuable baseline information for a subsequent proposal with the goal of understanding the dynamics of this karst system during the Holocene. This will enable to determine possible causes of drastic seasonal lake level changes as well as on the recurrence rates, and their effects on aquatic and terrestrial species, biodiversity and genetics through paleolimnological and paleo-genomic analysis.