Mercury, algae made water undrinkable in heart of city

Reservoirs in the heart of an ancient Maya city were so polluted with mercury and algae that the water likely was undrinkable. Researchers found toxic levels of pollution in two central reservoirs in Tikal, an ancient Maya city that dates back to the third century B.C. in what is now northern Guatemala. New findings suggest droughts in the ninth century likely contributed to the depopulation and eventual abandonment of the city.

David L. Lentz, Trinity L. Hamilton, Nicholas P. Dunning, Vernon L. Scarborough, Todd P. Luxton, Anne Vonderheide, Eric J. Tepe, Cory J. Perfetta, James Brunemann, Liwy Grazioso, Fred Valdez, Kenneth B. Tankersley, Alison A. Weiss. Molecular genetic and geochemical assays reveal severe contamination of drinking water reservoirs at the ancient Maya city of Tikal. Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-67044-z

Understanding civilizations of the past and how they emerge and eventually falter is a primary research focus of archaeological investigations because these provocative data sets offer critical insights into long-term human behavior patterns, especially in regard to land use practices and sustainable environmental interactions. The ancient Maya serve as an intriguing example of this research focus, yet the details of their spectacular emergence in a tropical forest environment followed by their eventual demise have remained enigmatic. Tikal, one of the foremost of the ancient Maya cities, plays a central role in this discussion because of its sharp population decline followed by abandonment during the late 9th century CE. Our results, based on geochemical and molecular genetic assays on sediments from four of the main reservoirs, reveal that two of the largest reservoirs at Tikal, essential for the survival of the city during the dry seasons, were contaminated with high levels of mercury, phosphate and cyanobacteria known to produce deadly toxins. Our observations demonstrate severe pollution problems at a time when episodes of climatic aridity were prevalent. This combination of catastrophic events clearly threatened the sustainability of the city and likely contributed to its abandonment.

Figure 4
Figure 4 - Cyanobacteria molecular genetic results from four reservoirs at Tikal. Evidence of cyanobacteria, or blue-green algae, blooms of Planktothrix and Microcysitis (both known to produce highly toxic microcystins) were found in the Temple and Palace Reservoirs. Taxa marked with an “*” denote unclassified strains.