Mexican Meromictic Lakes: What We Know So Far

Abstract

The climate, geology, and physiography of the Mexican territory resulted in a large diversity of inland aquatic bodies. So far, only a few meromictic lakes have been reported from different regions of Mexico , covering a vast range in latitude (≈16–26 °N), longitude (≈87–102 °W), and altitude (≈7–1700 m a.s.l.). The meromixis in Mexican lakes has been caused by one or more of the following factors: (a) coastal lakes where the interaction of freshwater and seawater in karst zones take place, (b) lakes located in semiarid and arid areas where evaporation greatly surpasses precipitation, and (c) deep lakes with relatively small surface area that lack complete circulation. The origin of the Mexican meromictic lakes is primarily due to solution (e.g., sinkholes) and secondarily due to volcanic activity. The Mexican meromictic lakes are small or large, shallow or deep, with either turbid mixolimnion or transparent mixo- and turbid chemolimnion , with diverse temperature profiles from thermal inversions to subsurface maxima or double thermocline, with one and up to three haloclines showing from subtle to quite large salinity ranges and thickness from few cm to up to tens of meters. The DO profiles are typically clinograde or with a subsurface maximum; pH is alkaline in the mixolimnion but varies from acidic to alkaline in the monimolimnion ; and nutrient concentrations range from low to high. It seems the factor(s) leading to meromixis have no effect in producing physical, chemical, or biological characteristics in lakes. Mexican meromictic lakes display a mosaic of environmental and ecological features.