Lidar map of Tikal highlighting some of its reservoirs. Image adapted Tankersley et al. 2020. Lidar-derived hillshade image created by Francisco Estrada-Belli of the PAQUNAM LiDAR Initiative. Used with permission. Graphic modified by Bryan Lin.
Currently, about 2 billion people worldwide don’t have access to safe drinking water, and roughly half of the world’s population is experiencing severe water scarcity for at least part of the year. And, according to the United Nations, these numbers are only expected to increase—exacerbated by climate change and population growth.
For example, as the Earth warms, water supplies stored in glaciers and snow cover are projected to further decline, reducing water availability during warm and dry periods. Climate-inducted sea-level rise is projected to extend salinization of groundwater, decreasing freshwater availability for humans and ecosystems in coastal areas. Water quality is also affected by climate change—as higher water temperatures and more frequent floods and droughts are projected to exacerbate many forms of water pollution.
Right now, only 0.5% of water on Earth is useable and available freshwater, with climate change dangerously affecting that supply. Now, researchers at the University of Illinois at Urbana-Champaign are championing an idea they think can help—and it’s not a new one. In fact, it’s extremely old, dating all the way back to the Ancient Maya civilizations of 600 to 800 C.E.
The Maya built reservoirs that provided potable water for tens of thousands of people in cities during the annual five-month dry season, and even in periods of prolonged drought. The reservoirs relied on aquatic plants to filter and clean the water. Today, that’s called a constructed wetland, and study author and anthropology professor Lisa Lucero suggests the modern world needs more of them if we are going to survive climate change and an increasingly warming world.
What’s old is new again
Constructed wetlands are engineered systems that use the natural functions of vegetation, soil and organisms to provide secondary treatment to wastewater.
The Ancient Maya did this by using a variety of aquatic plants, most of which still populate Central American wetlands today. These plants, including cattails, sedges, reeds and water lilies, helped filter the water, reducing murkiness and absorbing nitrogen and phosphorus.
Archeologists have identified all of these plants in sediment cores from Maya reservoirs, but the water lily, or Nymphaea ampla, tells us the most about the construction of the ancient reservoirs.
Water lilies can only thrive in clean water, in environments without acidic conditions or too much calcium, like limestone.
To keep water lilies alive, water managers would have had to line the reservoirs with clay. A layer of sediment would be needed for plants’ roots. In turn, the water lilies and trees and shrubs planted near the reservoirs shaded the water, cooling it and inhibiting the growth of algae.
“The Maya would have had to dredge every several years… (and) harvest and replenish aquatic plants,” explains Lucero. “The nutrient-laden soils and plants removed from reservoirs could then be used to fertilize fields and gardens.”
The Maya were also careful not to build residences near reservoir edges so as to avoid runoff and contamination seeping through the terrain.
Evidence suggests Maya reservoirs supplied potable water to people for more than 1,000 years, failing only when the severest droughts took hold in the region between 800 and 900 C.E. In her research, Lucero says that current climate trends will require many of the same approaches the Maya employed, including the use of aquatic plants to improve and maintain water quality naturally.
“Constructed wetlands provide many advantages over conventional wastewater treatment systems,” said Lucero. “They provide an economical, low technology, less expensive and high energy-saving treatment technology.”
In addition to providing clean water, constructed wetlands also support aquatic animals and can be a source of nutrients to replenish agricultural soils.
“The next step moving forward is to combine our respective expertise and implement the lessons embodied in ancient Maya reservoirs in conjunction with what is currently known about constructed wetlands,” said Lucero.