Dedicated to Conserving the Pristine Ecology of Laguna Bacalar Bacalar, Quintana Roo, Mexico
1. Laguna Bacalar Sublacustrine Ecology and Biogeochemistry: the influence of cenote coupling.
Laguna Bacalar is an important site for gaining a better understanding of how humans interact with fragile environmental systems. This relationship remains one of the great scientific challenges of our time. Worldwide, freshwater demand exceeds supply; however, the Yucatan Peninsula, and specifically the Laguna Bacalar area has a luxury freshwater supply, however the manner in which human development interacts with the water resources of the area has severely reduced usability and created a highly fragile co-existence between the two. Laguna Bacalar is one of the most visibly beautiful lakes on the planet. In fact, put on the table photos of all world class lakes and choose one that is visibly unique-- virtually everyone will pick Laguna Bacalar. This exercise directly translates the visible uniqueness of Laguna Bacalar into a unique ecology and biogeochemistry. Water clarity of this oligotrophic, nitrogen limited system is superb, however, the eutrophication potential as a result of increasing seepage, point and non-point discharges looms large. If the lake reaches its nutrient load thresholds a series of ensuing ecological/biogeochemical changes will likely occur. Laguna Bacalar has many characteristics of the Caribbean including sharing its beautiful hues of turquoise and blue, prompting the ancient Maya to name it "Laguna de Siete Colores" (Lake of Seven Colors). Several marine species have adapted to the Laguna’s freshwaters and also freshwater stromatolites, mangroves, some saltwater fishes (e.g., tarpon, bone fish and skate), and resident cichlids and crocodilians. Sublacustrine cenotes (karst sink holes) are located both within the lake itself and on its adjacent shores. The most notable of the land cenotes is believed to be 200 meters deep (some suspect much less) and has a rich cultural history--the Maya believed they were spiritual places. The Yucatan Peninsula is composed mainly of limestone which is highly permeable and soluble. Dissolution of the rock has created a karst topography with sinkholes (cenotes). High precipitation in the rainy season directly infiltrates to the underground through fractures and sinkholes, then flows through the porous and fractured media and finally discharged to the sea or surface waters such as Laguna Bacalar. The peninsula is perhaps the largest freshwater lens system in the world. A fresh water lens, resulting from the infiltration of rainwater, overlies seawater and in the peninsula is thin due to intrusion of the sea water. In areas close to the marine coastline, groundwater becomes saline below 5 or 10 m from the surface. Most extraction wells for water supply are located in the interior about 20 or 30 km from the coastline where the fresh water lens is developed to the depth of around 50 m. However, over exploitation via over pumping the aquifer and contamination by sewage may cause local salinization of the freshwater lens by salt water intrusion and by the breakdown of the halocline density barrier between the two. These processes along with rapidly increasing commercial development directly threaten the pristine waters of Laguna Bacalar. The lake today is on the cusp of becoming one of the most threatened lakes in the world. Recently discovered by the tourism industry, construction of new accommodations is accelerating rapidly, yet there is no concomitant effort for environmental protection, e.g. there is no infrastructure for sewage treatment and little ecological scientific data are available. The area is rated at the highest conservation priority of the entire Caribbean ring (Marxan output, Modeled Conservation Priority, Caribbean).
Cenotes are of two types, those on land and those that are sublacustrine (submarine). The cenotes on land have been studied by the archeological community and others. Our work centers on the sublacustrine cenotes, specifically those of Laguna Bacalar that have never been studied. While the land cenotes are more abundant than the sublacustrine cenotes, the latter are of particular interest because they are the direct conduits of freshwater exchange between land and Laguna Bacalar. It is well documented that Maya used the land cenotes as ceremonials sites, however their use of the sublacustrine cenotes is not documented (unstudied). Our work focuses on the freshwater exchange and cenote ecology (rather than their archeology). The Instituto Nacional de Antropología e Historia (INAH) is advised of our work.
Cenotes found in the Yucatan Peninsula are either land based or underwater (sublacustrine or submarine). The sublacustrine cenotes in Laguna Bacalar are karst formed extensions from the underground freshwater lens network of aquifers that exit in the Laguna to the extent that Laguna Bacalar can be viewed as an extension of the underground freshwater aquifer. Thus, the sublacustrine cenotes provide an important window for measuring the interface of water exchange between the Laguna and the City of Bacalar, population 10,000 and the largest community on the lake, and the most ecologically threatening to Laguna Bacalar. It is believed that the sublacustrine cenotes have never before been studied for their ecological or archeological contribution (we are communicating with Universidad Autonoma de Yucatán Archeology to participate in the videography and other studies of the cenotes). While the Maya used the land cenotes extensively for ceremonies, it is not known if the sublacustrine cenotes were used similarly. Several of the sublucustrine cenotes lie near the shore allowing access, but would seem more problematic for hosting ceremonies than land cenotes.
Specific Exploration and Research Objectives:
The research objectives will provide information related to exchanges via the underground conduit from the City of Bacalar, the paleolimnological history, and ecological changes in the Laguna.
1) Initial visual exploration of submerged cenotes. A small Video Ray ROV capable of diving to depths up to 500 feet will be deployed in the sublacustrine cenotes to acquire video and still photography of cenote structure. This will document substrate characteristics that may provide valuable data on groundwater seeps into the cenote. It will also document the debris field status of the cenote and presence of possible archeological finds. The ROV observations also will determine the sampling locations to facilitate the safe sampling of the substrate for the paleolimnology core retrieval using the benthos corer.
2) Collection of in situ, real time data on temperature, conductivity, oxygen, and pH as a function of depth via a sensor package outfitted on the ROV. These measurements will assist in determining the existence of fresh groundwater inflows or marine saltwater intrusions nearer the bottom of the cenotes. Laguna Bacalar rests in the Bacalar fault that may be impervious to saline intrusion; however the subterranean saltwater under the freshwater lens could seep to the cenotes. If this is the case the density and salinity structure within the cenotes may be harbingers of salt water intrusions and useful in monitoring the degree of sea water intrusion into the freshwater lens. This would have a direct impact on the resource management of freshwater supplies and their utilization. Additionally, nitrogen and phosphorous nutrient data, chloride, total alkalinity, CaCO3 hardness, will be analyzed from waters of the cenotes.
3) Examine the utility of geochemical tracers as tools for estimating ground water inputs to the cenotes and to the lake. Profiles (surface to bottom) of radon-222 will be measured in lake and cenote waters collected by pumping from the ROV or via Niskin bottles. Radon-222 is a short lived (half life = 3.8 days) naturally occurring radioactive noble gas produced in the U-238 decay series from radium-226 (half life = 1600 years). Ra-226 present in the carbonate rock can support high activities of radon-222 dissolved in ground water. Radon has frequently been used as a tracer for submarine ground water discharge and for estimating ground water inflow into nearshore areas (e.g. southeast Atlantic shelf, off the Everglades in Florida Bay, deep groundwater inflow into the Gulf of Mexico, etc., see e.g. Cable et al 1996). The high void karstification of the Yucatan should accentuate radon levels and the relatively rapid movement of groundwater over relatively long distances. The sublacustrine cenotes may serve as a focal point for groundwater inflow, much like sink holes observed in carbonate formations in the Great Lakes (Biddanda et al. 2006). The observation of excess radon-222 in the bottom waters of the cenotes may serve both to identify the existence of groundwater inflow and to estimate inflow rates.
4) Determine the recent 150 year paleolimnology and ecology of the cenotes and Lake Bacalar using the sub-fossil profile history recorded in the sediments of the lake and cenotes. Profiles of fauna and flora fossil remains may yield valuable information on ecological trends, hurricane perturbations, and also cultural changes along the lake’s shore over the last 150 years. Gravity cores will be collected, sectioned, and dated using Pb-210 and Cs-137 (if applicable) geochronologies (Robbins and Edgington 1975). Subsamples will be examined for geochemical (organic C, nitrogen, phosphorus, C and N stable isotopes) and biological indicators of the ecological history (e.g. storm events, terrestrial inputs, eutrophication, species changes, etc.) of the system.
5) Quantitatively establish the population structure of the dreissenid blacked striped mussel (Mytilopsis sallei) to develop background level data. Sublacustrine cenotes are the ‘point source’ conduits of land generated activity potentially leading to nutrient enrichment and enhanced growth of black striped mussel populations. This work will establish reference data by which long term comparisons can be made. The black striped mussel, a cousin of the zebra mussel (Dreissena polymorpha), is as ecologically lethal as the zebra mussel in upper North America. At the moment, the black striped mussel in Laguna Bacalar is likely the only worldwide example of an invasive dreissenid appearing to be in ecological balance. However, this mussel will be one of the first responders to nutrient enrichment, reaching unprecedented population numbers similar to the zebra mussel in North America. If enrichment of the Laguna advances, food web and nutrient cycling perturbations, the severe over-colonization by dreissenids as seen elsewhere, and probably the destruction of the Laguna Bacalar unique freshwater stromatolites may ensue. Sala et al. (2000) noted that among other systems, lakes and cenotes are especially vulnerable to ecological disruption from invasive species
This study will involve counts of blacked striped mussels that currently live on natural hard substrates in the Laguna, and also from artificial substrates placed in the Laguna. The methodology will follow accepted practice and scientific rigor (replicated samples and statistical inference) used for zebra mussel monitoring in North America that have been studied extensively by Dr. Kaster for monitoring the colonization of zebra mussels in the Great Lakes since their arrival (20 years), and supported by funding from NOAA Sea Grant, U.S. Army Corps of Engineers, and major industries.
3. Comparative Biogeochemistry and Ecology of Submarine Cenotes in Laguna Bacalar, Mexico and Lake Huron, USA
These geographically distant systems represent two unique coupling ecosystems on earth. Understanding interface coupling of pristine systems remains one of the great scientific challenges of our time. Laguna Bacalar is a sentinel observatory for understanding of how humans interact with pristine land-freshwater-seawater coupled systems and the Lake Huron cenotes are novel within the Great Lakes. The sublacustrine cenote sinkholes of Laguna Bacalar are exchange conduits of the land-freshwater-seawater triad that have never been explored. Whereas Laguna Bacalar cenotes are characterized by a seawater lens the Lake Huron sinkholes have a groundwater lens. Thus the two systems present an intriguing opportunity for comparative biogeochemistry and ecology.
Few know of this 35 mile long freshwater lake, but Laguna Bacalar is Mexico’s 2nd largest natural lake and one of the world’s truly unique lakes, hidden by the dense Yucatan jungle. Laguna Bacalar is one of the most visibly beautiful, undeveloped lakes on the planet. This visual uniqueness directly translates into a unique biogeochemistry and ecology. Laguna Bacalar has many characteristics of the Caribbean including sharing its beautiful hues of turquoise and blue, prompting the ancient Maya to name it "Laguna de Siete Colores" (Lake of Seven Colors). Several marine species have adapted to the Laguna’s freshwaters as have freshwater stromatolites, mangroves, some saltwater fishes (e.g., tarpon, bone fish and skate), and resident cichlids and crocodilians. The Yucatan Peninsula is composed mainly of limestone which is highly permeable and soluble (it has been described as Swiss cheese limestone; and numerous underground rivers flow to the Caribbean). This freshwater/saltwater lens is the largest known continuous lens system in the world.
The sublacustrine cenotes in Laguna Bacalar are karst formed extensions from the underground freshwater lens network of aquifers that exit to the Laguna, and that lie above and are density supported by sea water from the Caribbean. Thus, the sublacustrine cenotes provide an important window for measuring the interface flux of water exchange. Communities inhabiting these extreme environments support unique food webs and biogeochemical pathways. The Lake Huron cenotes are known to have groundwater influx and there is evidence of a community continuum from shallow water photosynthesis to deep chemosynthesis in the same lake. Preliminary research on Lake Huron is documented by Biddanda, et al. 2007: Exploration of a submerged sinkhole ecosystem in Lake Huron, have shown that photosynthesis-dominated shallow sinkholes give way to chemosysnthesis-dominated deep-water sinkholes in Lake Huron. It is not known if this relationship applies to Laguna Bacalar cenotes.
The cenotes on land have been studied by the archeological community and others. Our work centers on the sublacustrine cenotes, specifically those of Laguna Bacalar that have never been explored and which will allow a direct function comparison with the Lake Huron cenotes. It is well documented that Maya used the land cenotes as ceremonials sites; however their use of the sublacustrine cenotes has also not been explored. While our work will focus on the freshwater exchange and cenote ecology, vigilance for archeological evidence will be high. The Instituto Nacional de Antropología e Historia (INAH) will be advised of our work with the opportunity to participate in the first ever ROV explorations.
Exploration and Research Objectives: The research objectives for the two sites will provide a comparative biogeochemistry related to exchanges via the underground conduits and ascertain ecological relations of the Laguna Bacalar cenotes and Lake Huron sinkholes.
1) Initial visual exploration of submerged cenotes. A small ROV capable of diving to depths up to 400 feet will be deployed in the sublacustrine cenotes to acquire video and still photography of cenote structure. This will document cenote structure and substrate characteristics that may provide valuable data on groundwater seeps into the cenote. The ROV will also reconnaissance the debris field status of the cenotes for benefiting the deployment of the underwater mass spectrometry instrumentation.
2) Collection of in situ, real time data on temperature, conductivity, oxygen, and pH as a function of depth via a sensor package outfitted on the ROV. Additionally, a portable underwater Membrane Inlet Mass Spectrometry-MIMS system, capable of high throughput simultaneous detection of multiple analytes: methane, nitrogen, oxygen, hydrogen sulfide, argon, carbon dioxide, will be used to observe important phenomena in the deep-cenote (e.g., hydrothermal venting, sea water intrusion, and benthic fluxes, including those emanating from methane hydrates). These measurements will assist in determining the existence of fresh groundwater inflows or marine saltwater intrusions nearer the bottom of the cenotes.
3) Naturally enriched radionuclides of radium (Ra) and their daughters (eg., Radon, Rn), will be used to quantify both the vertical and horizontal mixing rates of groundwater plumes entering the cenotes as well as quantify the amount of water discharged from these sinkhole vents. Because these radiochemical tracers decay with known and differing half-lives (100’s of years to days), they can be used to estimate the relative ages of various processes, like mixing, simply by measuring the inherent properties found within the waters naturally. Among the tracers high in these groundwaters is Rn-222, a noble gas with a 3.8 day half life. Ra-226 present in the carbonate rock can support high activities of Rn-222 dissolved in ground water, which has frequently been used as a tracer for submarine ground water discharge and for estimating ground water inflow into nearshore areas (e.g. southeast Atlantic shelf, off the Everglades in Florida Bay, deep groundwater inflow into the Gulf of Mexico, etc.). The high void karstification of the Yucatan should accentuate radon levels and the relatively rapid movement of groundwater over relatively long distances. The sublacustrine cenotes may serve as a focal point for groundwater inflow, much like sinkholes observed in carbonate formations in Lake Huron. These radiochemical clocks may also be useful in estimating the age of groundwater in the sinkhole and relate that to the time scale of production or loss of other biogeochemically interesting constituents, like methane, oxygen, hydrogen sulfide, etc.
4) Comparative microbial communities of the two systems will determine dominance patterns of photosynthetic and chemosynthetic autotrophs along the vertical axis of the cenote habitats. The continuity (ecocline) of photosynthetic and chemosynthetic (Beggiatoa:proteobacteria) communities was discovered in fumaroles in Yellowstone Lake, USA, in the 1980s, but little is known of the dynamic interaction. In situ-MIMS will provide critical insights into such unique autotrophic relationships in the sublacustrine cenotes in Lakes Bacalar and Huron and allow comparison to other similar ecosystems.
4. Interfacing Laguna Bacalar Science and Community Stewardship
The Institute's mission is to draw attention to Laguna Bacalar's world class ranking from scientific based organizations, conservation minded groups, and world governmental bodies especially those that also have lakes of this stature. It is believed that by drawing attention to this unique Mexican natural treasure, those bodies capable of stewardship will be linked together to build the political, economic, business, and scientific consortium necessary to effectively preserve Laguna Bacalar. To do nothing will accelerate the gradual degradation of Laguna Bacalar and loss of this world treasure. As part of this stewardship effort it is critical in the Laguna Bacalar cultural setting to bridge science with community participation. Mexican and some international scientists are well aware of the groundwater and sanitation problems of the Yucatan Peninsula and numerous groups are working to bring this to the attention of both world and local communities.
There is a rich and complicated cultural history blended with contemporary economic issues that sets the backdrop in this region. The reality is that underlying issues still exist from the indigenous Caste War of Yucatan, ending in 1902. There are growth 'sensitivities' in this region not only among the Maya but also some villagers and rural folk. It has been expressed that these groups seem 'disconnected' from the rapid expansion of events that is occurring at Laguna Bacalar. This effort is intended to help bridge that gap.
This is a grass root effort to directly involve local participation in this international effort. The participatory outreach activities will first, thread communication paths into the community through a series of family theme events centered on Laguna Bacalar, and through the local schools. Second, a 'minds-on and hands-on' involvement for adults. Third, an investigative program for young people. Fourth, the formation of a community liaison group active in disseminating Laguna Bacalar science information to the community.
2. Impact of Archeology Tourism/Ecotourism on Laguna Bacalar
Few know of this 35 mile long freshwater lake, but Laguna Bacalar is Mexico’s 2nd largest natural lake and one of the world’s most unique lakes. The dense Yucatan jungle and tourist distractions such as Cancun and the Caribbean Riviera Maya coast have helped keep this secluded lake obscured, however commercial development is beginning to spill southward into the Costa Maya and Laguna Bacalar. The Bacalar area is growing rapidly and exceeds the infrastructure capacity to support tourism without seriously impacting the lake.
The new Ichcabal archeology site only a few kilometers from Bacalar. The ruins are as magnificent as others contemporary Mexico and Central America, such as the Pyramid of the Sun in Teotihuacan and Cholula, both in Mexico and the archaeological site of El Mirador-Nakba, in the Laguna del Tigre National Park, in the jungle Peten, Guatemala.* The largest building in the complex is 45 meters tall.* The ruin were discovered in ca. 1995 and have been excavated since that time. It is said, but not confirmed that it will open in about 5 years, or 2014. Adriana Velazquez, director of the National Institute of Archeology and History, has indicated that this find will be a 'turn around' event for the region.
This archeological find has made it imperative that research linkages be formed between professionals in archeology, ecotourism, and aquatic science that focus on potential impacts to Laguna Bacalar, Mexico's emerging world class lake.
*Alberto Cabezas/El Universal, 2005