Water chemistry of lakes related to active and inactive Mexican volcanoes

Water chemistry of crater lakes, maars and water reservoirs linked to some Mexican volcanoes within and outside the Mexican Volcanic Belt has been determined for several years and examined regarding environmental and volcanic factors. All the analyzed lakes are relatively small with a maximum depth of 65 m, and are located in regions with different climates, from semi-arid to very humid, with altitudes ranging from 100 to more than 4000 m a.s.l. Crater lakes in active volcanoes (El Chichón, Popocatépetl) have very low pH, moderate to high temperatures and major ion concentrations varying with the level of volcanic unrest. Lakes in sub-arid and temperate-arid regions (like maars in Puebla and Guanajuato states) show high alkalinity and pH, with bicarbonate/carbonate, chloride, sodium and magnesium as predominant ions. Lakes located in humid climates (Central Michoacán and Veracruz state) have low mineralization and near-neutral pH values. In general, conservative dissolved ions and conductivity appear to be mostly controlled by precipitation/evaporation and by the ionic concentration of groundwater inputs. Calcium, magnesium, sulfate concentrations and pH are strongly influenced by volcanic-rock or volcanic gas interactions with water. The influence of low-level volcanic activity on crater lakes may be obscured by water–rock interactions, and climatic factors. One of the aims of this paper is to define the relative influence of these factors searching for a reference frame to recognize the early volcanic precursors in volcano-related lakes.