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Freshwater Resources in the Yucatan Peninsula Sam Meacham1 Founder of CINDAQ (Centro Investigador del Sistema Acuifero de Quintana Roo) Introduction Freshwater: the one resource that we human beings depend on more than anything, and the one that most of us take for granted. As we enter the 21st century, world attention is turning to dwindling freshwater reserves and the need to conserve them for future generations. To find a large pristine freshwater supply in this world is rare. Mexicoâs YucatÃ¡n peninsula contains such a resource. Made up of the states of Campeche, YucatÃ¡n, and Quintana Roo, the peninsula is a land rich in both human and natural history. Dominating the landscape are temples and pyramids that testify to the achievements of the ancient Maya civilization. Today, the Mayan culture still thrives on the peninsula with many traditions and a strong cultural identity intact. Below the ground runs a common thread that has woven the fabric of life and directed the distribution of life on the peninsula for millions of years; the world of the cenotes and underground rivers. These underwater labyrinths are part of an intriguing puzzle that explorers and scientists are only just beginning to piece together. Along Quintana Rooâs Caribbean coast, breakneck development from Cancun to Tulum threatens the freshwater reserves. Formation of the Aquifer A combination of geologic events and climatic change has led to the development of these unique ecosystems. Limestone comprises much of the bedrock of the peninsula. Over countless thousands of years, rainwater, mixing with carbon dioxide formed a weak solution called carbonic acid that dissolved the limestone, forming rivulets that carved out the cave systems. During the last Ice Age, water levels of the world's oceans were approximately 100 meters (300 feet) lower than their present day levels. The caves of the YucatÃ¡n peninsula were dry during that period. When the Ice Age came to a close 18,000 years ago, the climate of the planet warmed up, the glaciers receded, and the caves flooded as sea levels rose. What is certain is that these flooded cave systems play an important role as conduits for freshwater traveling from the jungle interior to the Caribbean Sea, making them the critical link between every major ecosystem in the region. Along the way they are used 1 Sam Meacham is the founder of CINDAQ (Centro Investigador del Sistema Acuifero de Quintana Roo) which is exploring and mapping the coastal cave system of the Yucatan. Sam Meacham and other cave divers are working with scientists to access the impact of development on the areaâs fragile water sources. 6
as the primary source of potable water for the population, and, unfortunately, as a convenient place to dispose of waste. Development Threatens Rapid development of the coast of Quintana Roo has set the stage for the underground rivers and the aquifer they serve to be detrimentally affected. In the last seven years, the 120-kilometer (80 mile) strip of beach known as the Riviera Maya has seen an explosion in growth. It is among the fastest growing areas in Latin America with an annual growth rate estimated to be between 20-25%. Behind this boom is the tourist industry, which, while creating jobs, has placed great stresses on the environment. It has taken only seven years for the Riviera Maya to equal the number of hotel rooms that took nearby Cancun 25 years to build. Filling these 22,000 rooms are an estimated 1.7 million tourists who visit the Riviera Maya each year. Moreover, many of the regionâs major attractions are located along the Riviera Maya, meaning that the millions of visitors to Cancun and cruise ship passengers landing in Cozumel are leaving their footprint as well. Much of the area development has been based on the premise that it is âeasier to ask for forgiveness than permissionâ in that building often takes place before any permits are requested. This philosophy coupled with inadequate waste disposal laws and their spotty enforcement has set the stage for a potential environmental nightmare. Urban sprawl has followed. In the most dramatic example, Playa del Carmen, which had a population of 10,000 in the early 1990âs, is now estimated to have a population approaching 120,000. Basic sanitary infrastructure has not been able to keep up with this rapid growth. Figure 1 Subterranean water flow. The two main threats for contamination of the freshwater aquifer are sewage and solid waste. The majority of the local population lives without the benefit of proper sewage treatment or storm sewers. Inadequately built septic tanks leach raw sewage directly into the freshwater aquifer. In some cases it is dumped directly into cenotes, the naturally occurring entrances to these flooded cave systems. 7
By law, all major hotels are required to have waste treatment facilities. Treated wastewater is injected into the bedrock at a depth that averages between 50 and 100 meters (150-300 feet). There are several flaws in this system. As illustrated in Figure 1 above, cave explorers, working with hydrologists have identified two levels of cave in the area. One is a shallow system that occurs between the surface and 20 meters (60 feet). It is within this system that freshwater is transported out to the sea. In addition, a deeper system has been identified extending down to 120 meters (330 feet). At this deeper level and at a distance of five kilometers from the coast, hydrologists have measured flow of salt water moving inland. At both levels the cave systems are immense with larger passageways exceeding five meters (18 feet) from ceiling to floor and widths of 20-30 meters (60-90 feet) or more. Figure 2 on the following page illustrates the potential that âdeepâ injection of sewage has to contaminate both of these levels and the many ecosystems that the caves connect. Figure 2 Potential of contamination from sewage injection. Due to the fact that the treated sewage is mixed with less dense freshwater and then injected into denser saltwater, it seeks the path of least resistance back to the surface, taking it directly into the freshwater aquifer and out to the sea. âDeepâ sewage injection in this hydrological context is an efficient way to not only contaminate the freshwater aquifer, but the ecosystems that these cave systems connect. Already, divers have witnessed the contamination of one cave system where high levels of fecal coliform were present. The other clear threat to the freshwater aquifer of the area is solid waste. It is estimated that the Municipality of Solidaridad generates approximately 200 tons of garbage a day. This garbage is transported and deposited into unlined landfills where it is burned. What 8
is left leaches a potent cocktail of contaminants through the porous limestone bedrock, directly into the freshwater aquifer. To see the consequences one only need look to Merida located in the state of Yucatan. Recent hydrologic studies leave no doubt that the first 20 meters (60 feet) of its 60 meter (198 feet) thick freshwater lens are unfit for human consumption due to widespread contamination by human waste (Marin and Perry, 1994). The Importance of Exploration and Mapping Over the last twenty years, dedicated cave diving explorers have discovered, explored and mapped more than 108 submerged cave systems and 450 cenotes and coastal lagoons in the area of the Riviera Maya. In total, over 480 kilometers (300 miles) of submerged passageway has been surveyed and mapped. The three largest underwater cave systems in the world: Sistema Ox Bel Ha, Sistema Nohoch Nah Chich, and Sistema Dos Ojos, all exist within 25 kilometers (15 miles) of each other (Gulden 2005).2 Two of them, Ox Bel Ha, and Nohoch Nah Chich, flow directly into the Caribbean Sea. Within the cave systems, 38 âstygobiticâ life forms have been identified. These âliving fossilsâ are providing scientists with information on chemosynthesis and the way in which life was distributed on earth. Anthropologists and archeologists, working with cave explorers, have identified important remains that are shedding light on prehistoric human settlement in the western hemisphere, not to mention the ritual and everyday use of cenotes by the ancient Maya. Plant life found within the moisture rich âmicroclimatesâ of cenotes is allowing botanists to study ancient Mayan plant use and cultivation techniques. Ornithologists are interested in studying what role cenotes play as stop over and wintering sites for the estimated 2 billion birds that migrate through the area every spring and fall. By combining survey data and observations made both inside and out of the caves, cave divers are allowing a broad picture of the areaâs aquifer and the ecosystems they connect to emerge. In addition to showing where the flow of freshwater comes from and goes to, the maps that cave divers produce form the foundation for scientific study, and easily allow the identification of potential threats to the freshwater resource of the area. There is no better example of this than the Ox Bel Ha System. Located to the south of the Tulum Archeological Site, Ox Bel Ha is an immense cave system, still in the process of being explored. Ox Bel Ha has over 121 kilometers (75 miles) of surveyed passageway, 72 interconnected cenotes and 3 freshwater exits into the Caribbean Sea. It is considered the 9th longest cave system on earth and is now considered the longest cave system in the Mexican Republic (Gulden 2005). This is made all the more remarkable by 2 There is no official tracking system for cave lengths. However, one often-cited source is Bob Gulden of Odenten, Maryland, who maintains the website âWorlds Longest Cavesâ http://www.caverbob.com/wlong.htm. As of November 4, 2005, this website listed the Ox Bel Ha system as the 9th longest cave system in the world and the longest underwater cave system with a recorded length of 88.765 miles (142854 meters) and maximum depth of 110 feet (33.5 meters). 9
the fact that it is completely submerged. In addition, Mayan archeological sites have been found both above and below the water, and there are prehistoric archeological sites within the cave that date back to when the caves were dry. Figure 3 The Ox Bel Ha Cave System and schematic of freshwater flow. As it winds its way beneath the surface, Ox Bel Ha passes through every major ecological zone in the area, emptying out onto the fringing reefs of Tulum (Figure 3). Each cenote within the system is an oasis of life, containing a variety of freshwater fish species, reptiles, amphibians, plant life, mammals and birds. Until 1998, Ox Bel Ha lay unexplored below the surface and would have remained so if it were not for a dedicated group of cave diving explorers seeking to find out what lay below. Without exploration efforts, an otherwise unknown natural wonder would have gone unnoticed. The impact of Ox Bel Ha on the surrounding area is not completely understood, however it is easy to see potential areas of concern. Figure 3 illustrates dramatically the far reaches of the Ox Bel Ha system. It is possible for a diver to enter a cenote at point âAâ and traverse the cave system, following the flow of freshwater exiting onto the coral reefs of Tulum at point âCâ. In total, it would be a traverse of over 8.5 kilometers (5 miles). Although this has yet to be done, it is important to realize that if a human being can make this journey, so too can any contaminant. Moreover, a passageway in the area of point âBâ that has yet to be explored indicates a major flow of freshwater heading in the direction of the Sian Kaâan Biosphere Reserve, an ecotourism and education center. 10
One only needs to see the current development plans for the area around Tulum (Figure 4) to see a very disheartening picture emerge. Urban development in this area has a direct effect on the freshwater resources and the ecosystems that Ox Bel Ha passes under including an internationally protected wildlife reserve. Without the maps that cave divers make, there would be no concern. Figure 4 Development plans for area around Tulum. Ox Bel Ha is just one example of many cave systems in the area that are threatened. What has been explored so far along the Riviera Maya is only a fraction of what exists. All exploration efforts to this date have been funded out of the pockets of the explorers themselves and from small donations from their friends and family. It is imperative that science follows behind the efforts of these cave explorers in order to better understand the complex hydrology of this extremely vulnerable aquifer. Cave divers are mapping the subaquatic cave systems. These maps are being analyzed to determine how the fracture and/or dissolution patterns can be reproduced numerically in order to simulate ground water flow in this complex aquifer system. 11
References Gulden, Bob. 2005. http://www.caverbob.com/wlong.htm. Visited 11.14.2005. Marin, L.E., and Perry, E.C, 1994. The Hydrogeology and Contamination Potential of Northwestern Yucatan, Mexico, Geofiscia Internacialonal, v. 33, 619-623. 12