5.1: Reading/Media

The central plaza at Tikal, Guatemala. In the remnant of the Corriental reservoir 1.5 km from the plaza, new finding of a sedimentary stratum comprising zeolite and quartz minerals suggests the ancient Maya people had developed water filtration systems. (Photo by Siyuan Chen.)

Water Filtration with Microporous Minerals in Preclassic Maya, 2,100 BP

Excerpt from "Zeolite water purification at Tikal, an ancient Maya city in Guatemala" by K.B. Tankersley, N.P. Dunning, C. Carr, et al. Scientific Reports 10, 18021 (2020). CC BY

Excerpt: Archaeologists have long believed that the indigenous people of the Western Hemisphere lacked any formal water filtration systems. In North America, ancient indigenous cultures obtained clean water from naturally filtered springs, used boiling, and earthenware pottery in which contaminants, silt, and clay were pulled to the sides of the vessel. In Mesoamerica, the Aztec relied on abundant artesian spring water brought into their cities (e.g., Tenochtitlan) through aqueducts, which did not require purification techniques. Aqueducts were also built by the Inca, which brought mountain spring water to cities in the Andean region of South America. The Maya were the only ancient New World civilization that needed water filtration because many of their cities were located on a karst landscape in a tropical and monsoon climate. While sand, gravel, plant, and cloth filtration systems have been documented in Egypt, Greece, and South Asia as early as the fifteenth century BCE, comparable data are lacking for the Maya region. There is no comparative case for Maya water purification systems, that is, there are no comparative data available. To date, excavations have been conducted in only a few dozen of the many thousands of ancient Maya reservoirs, and many of these excavations have been limited to a single test pit. Here we report our findings from Tikal, Guatemala, where zeolite was found in the one of the largest storage facilities of Maya drinking water in use during the Late Preclassic to Late Classic cultural periods (~ 2200–1100 yr. B.P.). The apparent zeolite filtration system at Tikal’s Corriental reservoir is the oldest known example of water purification in the Western Hemisphere and the oldest known use of zeolite for decontaminating drinking water in the world.

Tikal, known as Yax Mutal to the ancient Maya, was a city of more than 3000 structures situated in the karst topography and tropical forest ecosystem of the southern Maya Lowlands. Throughout the late Holocene, this area was affected by highly variable seasonal precipitation and subsurface drainage. In this environmental setting, the Maya constructed reservoirs to provide a reliable and sustainable source of drinking water during both seasonal and cyclical droughts.

The first systematic archaeological investigation of Tikal began in 1881 and accelerated through the twentieth century, resulting in detailed maps, photographs, and stratigraphic records of the site. 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. 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. Uncertainty remains about how these contaminants might have been removed from the drinking water. We reexamined three of the largest reservoirs at Tikal and a sinkhole as a control to evaluate the mineralogical composition and chronological contexts of the sediments in order to assess potential water purification methods and their time of implementation.

Our mineralogical and chronological analyses focused on three reservoirs (Corriental, Perdido, and Temple) and a control sinkhole known as inscriptions, that are separated by large independent catchment areas. The reservoirs were constructed and maintained from the early colonization of Tikal during the Late Preclassic period, ~ 2500 yr. B.P., until the abandonment of the city ~1100 yr. B.P. With the exception of the Corriental reservoir, all excavated reservoirs have stratigraphic discontinuities from dredging during ancient Maya times.

Figure \(\PageIndex{1}\): Maya cylinder vase (c. 700-800 CE), Guatemala. A ritual drinking vase depicting a king wearing a headdress adorned with water lilies. Water lilies symbolized sources of clean water in Maya culture. (Museum of Fine Arts, Boston.)

The mineralogy of the reservoir and sinkhole sediments was determined using X-ray diffraction (XRD) analysis. Sediment samples collected at 10 cm intervals from solid-sediment percussion cores, analyzed using XRD, and relative mineral percentages were calculated for each of the samples. XRD analysis demonstrates that all of the sediment samples contain similar quantities of the minerals calcite, smectite, and quartz. Calcite originates from the local Cretaceous-Tertiary limestone bedrock, which forms the karst landscape of Tikal and the South Petén basin. Smectite and quartz, however, are volcanogenic in origin. Smectite is a clay mineral derived from the terrestrial alteration of airborne acidic volcanic ash (i.e., glass). Similarly, microcrystalline quartz (~50 μm) in the reservoir sediments originated as airborne volcanogenic bipyramidal crystals known as “first quartz”. The ubiquitous co-occurrence of volcanogenic smectite and microcrystalline quartz in the reservoirs and sinkhole sediments suggests that volcanic ash accumulated episodically in the reservoirs throughout the occupation of Tikal. Pristine, sharp-edged, microcrystalline quartz and zircon crystals in the reservoir sediments also demonstrates that smectite arrived in the reservoirs and sinkholes, and across the southern Maya Lowlands from volcanic ash rather than erosion.

The mineral zeolite was found solely in the sediments of the Corriental reservoir where it was omnipresent and co-occurs with macro-crystalline (0.5–2.0 mm) euhedral quartz. There are ~ 50 distinct species of zeolites including analcime, clinoptilolite, and mordenite. In Guatemala, analcime occurs as an extensively altered form of jadeite and clinoptilolite and mordenite occur in association with the mineral’s quartz, calcite, and smectite in wet spring settings where volcaniclastic tuffs have altered to zeolites. While clinoptilolite and mordenite are not locally available at Tikal, they occur in volcanic rock cavities in western Guatemala where there are active, dormant, and extinct volcanoes. Clinoptilolite and mordenite have also been discovered in a coarse crystalline Cretaceous-Tertiary tuff exposed northeast of Tikal where clean potable water discharges. The co-occurrence of macro-crystalline euhedral quartz, zeolite, and clean drinking water was likely the symbolic connection and empirical basis for the Maya choosing to mine this resource.

Zeolite is a non-toxic, three-dimensionally porous, crystalline, hydrated aluminosilicate. Zeolite has adsorbent properties because its three dimensional microcrystalline pore spaces (3–4 Å) create a natural molecular sieve. Consequently, zeolite has the ability to filter out harmful microbes, nitrogenous compounds, and other dispersed insoluble and soluble inorganic and organic toxins from drinking water.

Corriental is one of the largest reservoirs (~58,000,000 L) at Tikal (Fig. \(\PageIndex{2}\)). Earthenware sherds of water jars of varying size were found in all of Corriental’s strata. 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. In this regard, Corriental is not only anomalous at Tikal, but throughout the Maya Lowlands. Corriental is also the only reservoir, which has evidence of a zeolite water filtration system.

The Corriental water filtration system was composed of clinoptilolite, mordenite, and coarse to very coarse sand-sized euhedral quartz crystals. These zeolites and macro-crystalline quartz are likely derived from a coarsely crystalline Upper Cretaceous tuff stratum exposed along lower margins of deep scarps defining the Bajo de Azúcar located ~ 30 km northeast of Tikal, where it forms an aquifer known locally for its clean water. The filtration system was likely held behind dry-laid stone walls with the zeolites and macro-crystalline sand-sized quartz crystals further constrained with woven petate (woven reed or palm fiber matting) or other perishable porous material positioned just upstream of, or within the reservoir ingresses, which were periodically ejected into the reservoir during flash floods caused by tropical cyclones. Evidence for these events can be found in the sequential crystalline quartz lenses in the reservoir sediments (Figs. \(\PageIndex{3}\)). Because zeolite crystals are much smaller in size (0.1 to < 10 μm), they were more easily water transported and deposited in the reservoir sediments during the functioning of the Corriental reservoir.

While a stand-alone coarse sand-size crystalline quartz filtration system would have been capable of water clarification, it would have had no effect on the removal of harmful microbes or deleterious insoluble or soluble toxins. Zeolite was a crucial component of the Corriental water purification system. At Tikal, zeolite occurs in the laminated organic clays of the Corriental reservoir sediments (Fig. \(\PageIndex{3}\)). These strata are indicative of a low energy depositional environment. The clays are interstratified with coarse sand-sized crystalline quartz deposited during periods of high-volume, fast-moving, storm flow. The stratigraphic reoccurrence of embedded macro-crystalline quartz strata suggests that the filtration systems likely had to be replaced following flash-floods.

The uppermost stratum in the Corriental reservoir containing zeolite and sand-sized macro-crystalline quartz dates to the Late Classic. This stratum represents the final destruction of the filtration system. In other words, the filtration system was not restored after this event. 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. 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.

Figure \(\PageIndex{2}\): (A) Location of Tikal in the southern Maya lowland. (B) The location of the Corriental, Palace, Perdido, Temple, and Tikal reservoirs, and the Inscription sinkhole and their catchment areas. (C) A lidar-derived hillshade image of the Corriental reservoir. (From Tankersley et al. 2020.)

Figure \(\PageIndex{3}\): (A) Soil horizons and sediments of the Corriental reservoir showing the location of anthropogenic quartz and radiocarbon ages yr B.P. (B) Relative percent of zeolite by depth. (C) Distinctive mineral XRD peaks. (D) Photomicrograph of anthropogenic euhedral quartz crystals and zeolite. (From Tankersley et al. 2020.)

Key Geologic Concepts:

Silicate minerals; SiO₄ tetrahedral network; ionic exchange; sun angle; seasons.

Supplemental Materials:

Article "Zeolite Clinoptilolite: Therapeutic Virtues of an Ancient Mineral" by A. Mastinu et al. Molecules 1517 (2019). CC BY