Anthropogenic impacts on tropical karst lakes: “Lagunas de Montebello,” Chiapas

The “Lagunas de Montebello” National Park (PNLM), Mexico, is a tourist destination well known for its crystal clear lakes surrounded by tropical rainforest. We selected four lakes, two pristine, and two deteriorated, to investigate the changes from transparent, blue waters to turbid, yellowish‐green that have been taking place in the past 15 years. Nutrient, chlorophyll a , seston, and particulate organic carbon concentrations were higher in the deteriorated lakes than in the pristine. Sediments in the deteriorated lakes were finer, with lower carbon and higher sulfur content than those in the pristine. Although the four lakes are karstic and belong to the same district (tropical cockpit karst), the pristine ones are on the SE intermountain zone fed mostly underground, whereas the deteriorated lakes are on the NW plateau area fed mostly superficially. Deteriorated lakes evolved from a pristine condition through receiving nutrients and/or organic matter from agricultural and urban/domestic wastewater, from both point and nonpoint surface sources. Pristine lakes have remained so by their insulation from surface water pollution. Nonetheless, karst lakes maintain a hydraulic connection with the groundwater so pollutants reaching the lakes superficially—or the groundwater that feed them—could be easily and promptly disseminated to other lakes in the district jeopardizing the still pristine lakes. The higher humidity and warmer temperatures of tropical karts areas escalate the fragility of these ecosystems exposed to human activities through, for example, heavy and sudden storm rainfalls and floods, favouring pollutants dispersion among lakes turning them highly vulnerable to water pollution and deterioration.