TOXIC ALGAL BLOOMS COINCIDE WITH MAYA OCCUPATION OF THE GUATEMALA HIGHLANDS

Climate change and terrestrial environmental impacts from erosion and deforestation are known stressors to ancient Maya societies. Whereas the scarcity of water during the Terminal Collapse and Classic Periods has been noted from sediment cores and speleothem records, much less is known concerning degradation in water quality. Harmful algal blooms, toxic cyanobacteria, and anoxia are frequent occurrences in modern societies where dense populations or extensive land use are adjacent to aquatic ecosystems. Here, we measured biomarkers for cyanobacteria and the cyanotoxin, microcystin, on a sediment core collected from Lake Amatitlán, Guatemala, which is currently in a toxic and hypereutrophic state. Paleolimnological evidence shows that historic periods of harmful algal blooms and cyanotoxin production coincided with Maya occupation during multiple time periods. The most intense periods of paleo-cyanotoxin production coincide with alterations to the water system of the Maya city of Kaminaljuyu while cyanobacteria maximum abundance coincided with heightened development of the rural Valley of Guatemala. These periods of hypereutrophication and toxin production rival the modern hypereutrophic state in both magnitude and toxicity. While water quality degradation is not considered to be a primary stressor to ancient Maya societies, the conditions of Lake Amatitlán during historic occupation could have impacted water potability as well as toxin transfer to crops and food sources associated with the lake. These historic hypereutrophic episodes demonstrate that cultural eutrophication is not a modern phenomenon and should be considered when reconstructing ancient societal stress.