Molecular genetic and geochemical assays reveal severe contamination of drinking water reservoirs at the ancient Maya city of Tikal

Abstract

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 9 th 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. The ancient Maya abandoned the major center of Tikal in the mid-ninth century CE and although scholars have studied this site intensively for the past 60 years, exactly how and why the city met its ill-fated ending have remained unanswered questions. Our investigations, combining novel aDNA and soil geochemistry assays, however, shed significant new light on the abandonment of this once-powerful political, ceremonial and commercial hub. Recent explanations for the downfall of Tikal have centered on population expansion 1,2 coupled with extensive landscape degradation 3,4 and a period of multidecadal droughts from 820 to 870 CE 5-11. Extended episodes of climatic aridity made the city especially vulnerable because it lacked access to permanent bodies of water such as lakes or rivers, and the groundwater table, approximately 200 m below the surface, was inaccessible using existing technology 12. Inhabitants relied on reservoirs that ringed the city and filled during the rainy season to provide water during the dry season 13-15. To enhance this water collection process, numerous large paved plazas in the site core of Tikal, e.g., the Great Plaza, the Plaza of the Seven Temples and the West Plaza 14-16 were canted to drain water into the reservoirs, particularly the Temple and Palace Reservoirs, during the rainy season for storage 14. In this study, we seek to bring about a greater understanding of the reservoir system at Tikal and how it played a crucial role in sustaining the inhabitants. In particular, we were interested in how the reservoirs were used and how they were maintained as sources of potable drinking water and water for irrigation. Towards this end, we collected sediment samples during excavations in 2009 and 2010 f...

Zeolite water purification at Tikal, an ancient Maya city in Guatemala

“…B.P., until the abandonment of the city ~ 1100 yr. B.P. 8 , 11 . With the exception of the Corriental reservoir (Fig.…”

“…Earthenware sherds of water jars of varying size were found in all of Corriental’s strata 11 . Corriental has only minor evidence of chemical pollutants and no evidence of blue-green algal blooms or other pollutants and it is the only excavated reservoir, which was not heavily dredged 11 , 12 , 15 . In this regard, Corriental is not only anomalous at Tikal, but throughout the Maya Lowlands (Sections S5 – S7 ).…”

“…The subsequent occurrence of anthropogenic mercury (Hg) in the Corriental reservoir likely originated from the weathering of artifactual cinnabar (HgS) in the numerous residential areas and burials within the watershed. Anthropogenically Hg contaminated soil within the Corriental catchment would have in-washed from these areas causing an uptick in Hg 11 (Section S9 ). While it is impossible to know why the water filtration system was not rebuilt, it is possible that the Maya no longer had access to the necessary raw materials.…”

“…While subsequent investigations documented the architecture and planning of Tikal’s water management system, including precise dimensions of the catchment areas, human-modified watersheds, reservoirs, and their carrying capacity, the issue of water purification remained unresolved 8 . Given the area is subject to extreme seasonal droughts, a large population, and long-term occupation, the drinking water of Tikal was prone to contamination from a plethora of microbial sources (e.g., cyanobacteria) and leachates from toxic minerals such as cinnabar 11 . Uncertainty remains about how these contaminants might have been removed from the drinking water.…”

Co-Occurrence of Cyanobacteria and Cyanotoxins with Other Environmental Health Hazards: Impacts and Implications

“…High concentrations of mercury, of phosphate consistent with eutrophic conditions, plus 16S rRNA amplicons indicating Planktothrix and Microcystis blooms (and thus potentially microcystins), have been found in dated sediment profiles from former reservoirs serving the ancient former Mayan city of Tikal in Guatemala. This potentially toxic combination may have contributed to the demise of the Mayan population and of the city in the ninth Century CE [ 144 ].…”