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Faced with population growth and environmental pressures, such as sea level rise between 3,000 and 1,000 years ago or droughts about 1,200 years ago, Mayan societies responded by turning tropical forests into complex wetland fields with channels to manage the quality and quantity of water.
These wetlands served as large-scale agricultural systems for the cultivation of avocado, corn and squash and were active during extreme climatic events, such as droughts and times of population expansion.
"These perennial wetlands were very attractive during the harsh Mayan droughts, but they also had to be careful about water quality to maintain productivity and human health," explains Sheryl Luzzadder-Beach, co-author of the study published in the journal. PNAS and researcher at the University of Texas at Austin (USA).
The new job is the first in combine images obtained by lidar –By means of an airborne laser scanner– with evidence of ancient excavations of four wetlands in the Rio Grande basin in Belize, covering an area of more than 14 km2.
The results reveal that one of them, the so-called Birds of Paradise, is five times larger than previously discovered. The scientists also found another even larger wetland complex in that country.
Thus the study shows that the Mayans had “earlier, more intense and far-reaching anthropogenic impacts”In tropical forests than previously known. "These large and complex networks of wetlands may have changed the climate long before industrialization, and these may be the answer to the question of how a great civilization of the rainforest fed," says Tim Beach, lead author of the study and researcher at the American university.
Higher gas emission
To unveil the vast field of ancient wetlands and canal networks, the team obtained 250 square kilometers of high-precision laser images to mapping the soil under the swamp forest canopy. Inside, the scientists discovered evidence of multiple species of ancient cultivated foods, such as corn, as well as shells and animal bones.
According to the researchers, the extension of these systems could increase carbon dioxide emissions with the burning of vegetation and methane. In fact, the greatest increase in this last gas between 2,000 and 1,000 years ago coincides with the formation of these channels, as well as those of South America and China.
"Even these small changes could have warmed the planet, which provides a sobering perspective for the order of magnitude of the largest changes during the past century that will accelerate in the future," emphasizes Beach.
The researchers hypothesize that the Mayan wetland footprint may have been even larger and imperceptible due to modern plowing, degradation, and drainage. The findings add to the evidence of early human impacts in the tropics, and hypothesize increases in atmospheric carbon dioxide and methane from combustion, preparation, and maintenance of these field systems that contributed to the early Anthropocene.
Timothy Beach et al. "Ancient Maya wetland fields revealed under tropical forest canopy from laser scanning and multiproxy evidence" PNAS October 7, 2019.