Study links mercury in Maya lakes to aquatic losses
Sediment from two lakes in Mexico shows mercury spikes alongside declines in aquatic organisms. Researchers interpret the changes as evidence of food-web collapse.
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Sediment from two lakes in Mexico shows mercury spikes alongside declines in aquatic organisms. Researchers interpret the changes as evidence of food-web collapse.
A study published in Science Advances of sediment from two lakes near ancient Maya communities on Mexico’s northern Yucatán Peninsula has linked periods of high mercury contamination with declines in aquatic life. The researchers interpret the changes as evidence of collapse across the lakes’ food webs, the networks of organisms connected by what they eat.
Earlier research found mercury contamination at Maya sites including Tikal in Guatemala. The new findings extend that evidence to the northern Maya lowlands, where records of mercury pollution had been sparse.
Lead author Matt Waters, a paleolimnologist and environmental science professor at Auburn University in Alabama, said sediment markers for bacteria, algae, cyanobacteria, shelled organisms and insect midges declined or disappeared. He interpreted the losses as a sign that mercury had reached multiple levels of the food chain.
At Coba, a mercury spike began around 250 AD and lasted about 150 years, near the start of the Maya Classic Period, which lasted from 250 to 920 AD. The broader rise began around 40 AD, peaked around 250–300 AD and returned to background levels around 520 AD. At Xcach, a spike ran from around 125 AD to 200 AD, followed by another around the time of Coba’s spike and a third from about 535 AD to 820 AD.
For the study published in Science Advances, researchers extracted sediment cores and radiocarbon-dated wood and charcoal fragments to establish when layers formed. They measured mercury concentrations across the layers, comparing them with modern sediment safety guidelines and preserved biological traces.
The study summary says mercury levels exceeded modern sediment safety thresholds by orders of magnitude for centuries. The researchers compared layers of lake sediment with those guidelines and examined preserved biological traces. They dated charcoal and wood fragments using radiocarbon, a method for estimating the age of once-living material,
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The Maya used cinnabar, a red mercury sulfide mineral, as a pigment and in ceremonies and funerary rites. The mineral is not naturally abundant around Coba and Xcach and may have been an important trade commodity there, the researchers said. Sediment from two other lakes showed no elevated mercury; the team proposed that mercury or cinnabar brought into the areas around Coba and Xcach later entered the lakes.
Co-author Savanna Wooten, a postdoctoral researcher at the Jones Center at Ichauway in Georgia, said residents might have been exposed through water or fish, but the sediment records do not show that they were. She said the research does little to link mercury directly to the demise of Classic-era Maya cities, while adding another environmental pressure to those documented for the period. The researchers described mercury-related deterioration in water quality as a possible additional stressor alongside documented climate-related reductions in water quantity.
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