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

拉坎多内斯是拉坎顿玛雅当地居民，他们观察到，墨西哥南部拉坎顿森林中最大的两个喀斯特湖泊梅萨博克湖和齐班纳湖的湖水水位在2019年7月的两周内急剧下降。梅扎博克湖(0.83 km2；Zmax=25m)完全干涸，而齐班湖(1.24 km2；Zmax=70m)水位下降约30m，大部分喀斯特湖泊水质良好，是人类重要的天然水库，也是水生和陆地生物的栖息地。水生生态系统干化具有深刻的生态环境效应，造成生物多样性和遗传多样性的丧失。作为地球科学家，我们认为这是一个千载难逢的机会，可以非常详细地研究这一戏剧性的环境事件的影响，并将这些结果用作过去环境记录中干燥事件的“现代类比”。因此，拟议的多学科项目的总体目标是开展为期两周的实地活动，利用新的和古湖泊、地球物理和地质分析来评估Metzabok湖和Tzibaná湖突然干涸的水文和生态影响。我们的首要任务是研究残留水体中水柱和表层沉积物的化学成分，并捕捉这种干燥事件的证据如何在湖泊沉积物中保存下来。通过对最上面的短岩心厘米进行高分辨率的多代理分析，并与该地区的气象数据进行比较，将推断最近干燥事件的演变。最后，我们将收集水生和陆地生物物种的敏感性和耐受性信息，以及生态变化的幅度。由于多种地质和水文因素控制着水的平衡，岩溶湖泊的水文是复杂的和不可预测的。地球物理和基础地质调查将对导致突然干旱的可能机制提供重要的见解。地球物理测量方法将使我们能够获得关于这两个湖泊的湖泊沉积物的几何形状和厚度的信息，这是未来古湖泊和古气候研究的重要信息。此外，将2018年湖泊被填满时的调查数据与直接从干燥的湖底收集的数据进行比较，为校准用于表征沉积物的水载地电和电磁方法提供了一个难得的宝贵机会。拟议的项目将为随后的提案提供有价值的基线信息，目的是了解该岩溶系统在全新世期间的动态。这将能够通过古矿物学和古基因组分析确定湖泊水位剧烈季节性变化的可能原因以及复发率，以及它们对水生和陆地物种、生物多样性和遗传学的影响。

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.