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Thursday, June 06, 2013

CUBA'S CAVES: AN OVERVIEW OF THEIR BIOLOGY AND GEOLOGY

BY TOM SAWICKI
Cuba
Cuba's geology is very complex, having been created by a series of events beginning with the tectonic forces that pulled North and South America apart during the early and middle Mesozoic era. These events included uplifting, oceanic and island arc volcanism and the deposition of sediments. The processes continued through the Cenozoic era and their products were fused together over time.
Cuba's complex geologic history has contributed to a remarkably diverse troglobitic (cave adapted) fauna. My studies on the evolutionary history of the Hadziidae (a family of amphipod crustaceans) brought me to Cuba in order to collect specimens, and to learn more about the ecology of Cuba s caves. In the process I was privileged to explore much of Cubas beautiful countryside and make some great friends.
Approximately 50 kilometers southwest of Havana lies a large karst region. Luis Piedra Cave is one of many caves in this area that provides access to phreatic water. On January 2, 2000, I traveled to this cave along with Abel Per??z, a Cuban scientist and the only certified cave diver in Cuba. Abel had been to this cave a few years back to collect troglobitic fish and assured me that Weckelia ceca, one of the species I was in Cuba to collect, would be in this cave.
The trail leading to Luis Piedra Cave was heavily overgrown and our guides slashed a path through the underbrush with machetes. The cave entrance is a small hole in the ground that drops down approximately three meters, opening into a large cavern containing an underground lake. When we shined our lights in the water I was completely surprised by what I sawdozens of blind cave fish!
Relative to epigean ecosystems, caves are energy-poor environments. Organisms that live in caves are often dependent upon allochthonous detritus (organic material from outside the cave, such as leaves or the bodies of dead animals) to filter into the caves. This material, along with the bacteria and fungi on them, is consumed by small invertebrates, which are then consumed by other animals, like fish, salamanders or crayfish. In order to support so many fish, there would have to be a large influx of organic material into this cave, and a sizeable population of small crustaceans.
We donned our snorkel gear and hopped into the lake. All around us were hundreds of small crustaceans, including mysids and shrimp, floating in the water column. The amphipods I had come searching for were living in clumps of roots that had pushed their way through the cave ceiling and into the water column. I was amazed to see dozens of specimens living within each clump of the roots.
Generally one has to dive a locality many times just to collect a few specimens. The energy coming into Luis Piedro Cave was relatively high due to a large colony of bats living in the cavern and the tree roots, which were used not only by the amphipods, but also by a species of troglobitic crayfish. These energy sources allowed for such high species richness. We collected only a small sample in order to put as little stress on the population as possible. We then put our cave gear together and prepared to explore the cave. On his previous visit Abel limited himself to snorkeling in the lake in order to collect the troglobitic fish. This cave was virgin. After checking a couple of blind leads we found a passage that may be the beginning of a large system. We laid about 150 meters of line at an average depth of six meters. The cave just kept going. On the way out we surveyed and checked a few side passages that seemed promising. Abel tells me that there are many more such caves in this area just south of Havana and most have never been dived before. Luis Piedra was not a beautifully decorated cave, but what it lacked in geological splendor it more than made up for by its biology.
On the south coast of Cuba, a type of cave occurs that is very different from the classic solution tubes of inland Cuba. These caves are slumping fracture caves. A few hundred meters offshore from the south coast of Cuba lies a wall that was formed due to tectonic rifting. The wall drops to great depths and places stress on the karst terrain, literally pulling the limestone apart along fracture lines. These caves are rectangular in shape with sheer walls that drop off to 30 meters or more.
The caves are also anchialinehaline waters that have an inland surface connection and subterranean connections to the sea. At the halocline, a sharp drop in dissolved oxygen occurs and a very unique fauna can be found. Remipedia, (the most primitive class of crustaceans) hadziid amphipods, thermosbaenaceans, shrimp and more live in this highly-specialized environment. These caves have no speleothems and often appear unstable. I recall a few instances where I looked up and saw rocks that must have weighed tons that appeared to be hanging precariously in place. Obviously one does not wish for any tectonic activity at that moment. Most of these caves do not go very far, but the downstream side of Carboneros Cave has been pushed for approximately 300 meters and has the potential to go even farther.
The fauna that are found in Cuba s caves are very similar to what scientists find in the anchialine caves of the Yucatan and the Bahamas. Cuba may have played an important role in the distribution of fauna across the northern Caribbean. Although these animals occur in caves throughout the northern Caribbean region, individual species are often endemic to a single cave. For instance, the amphipod species, Bahazdia cubensis n.sp., is found only in Carboneros Cave. Thus, if this cave is contaminated or destroyed, B. cubensis could be lost forever.
Bhazida cubensis
Carboneros Cave is interesting for another reason it is located in Playa Giron, better known here in America as the Bay of Pigs. This is a resort area, now complete with a museum dedicated to the Bay of Pigs conflict. The access road to the resort has a large billboard with a hand holding a submachine gun. A loose translation of the billboard is Where American imperialism was first turned back. If you needed it, the billboard provided a stark reminder of the political reality in Cuba.
The biological reality is also rather stark. Animals that are adapted to live in caves are highly specialized and sensitive to human perturbations. It has only been within the last few years that most of the troglobitic species living in the anchialine caves in the Caribbean region have been discovered. Anthropogenic influences are putting many of these species at risk of extinction just as we are beginning to learn of their existence. Global Underwater Explorers is dedicated to educating the public about the fragility of caves and the need for their conservation. It is up to the individual, however, to take make the effort to become more aware of the issues facing many caves. I firmly believe that those of us who use caves for our enjoyment should be actively involved in efforts to help preserve these natural wonders.

Setting up and attaching side mount cylinders

Diagrams below by Curt Bowen

Proper set-up of your side mount cylinders is essential to maintain proper buoyancy and streamlining. Cylinders mounted on your side must be positioned correctly for ease of use, safety, comfort, and proper swimming techniques. If your cylinders are hanging low and riding on your torso, the ability to navigate tight restrictions is lost and your streamlining is gone. Knowing how to rig your cylinders is essential for keeping them stationary in their correct position on your sides.

The cam strap

The cam strap is used to secure the tank to the lower or butt portion of your side mount harness. The cam strap must have a clip attached, which is used to clip off to your harness. The cam strap must also be positioned properly on your tank. To position the cam strap, slip it over the cylinder and tighten it by pulling the strap tight and closing the cam buckle. The distance from the top of the cylinder valve, where the cam strap is placed, varies depending on your chest length. A good rule of thumb is to measure from your armpit to just below your belt line. Place the cam strap the same distance from the top of the valve.

Tank buoyancy

Proper tank buoyancy is essential for proper trim and streamlining. Some types of cylinders, such as aluminum tanks, become buoyant as they are depleted. For these cylinders, you may need to attach hard weights to the cylinder cam straps in order to compensate for the buoyancy change. Hard weights can also be added to the cylinder cam straps to offset the buoyancy of wetsuits and dry suits. If additional weight is needed due to dry suit buoyancy, a standard weight belt can be used under your harness.

Cylinder bungee and right and left post cylinders

For proper streamlining, your cylinders need to be snug and up and under your armpits. The cylinder bungee on your side mount system is used to pull the valve of the right and left cylinders into your armpits. The bungee or rubber tubing goes over and around the cylinder valves, pulling them tight against side. You may be using rubber tubing or bungee cord to accomplish this, but whichever method you use, make sure your cylinders are properly fitted under your armpits.
For your cylinders to fit correctly under your armpits and to make it easier for you to access your cylinder valves, a right (standard) and left post valve is recommended for side mount cylinders. These are the same valves as used on a set of double cylinders without the cross over bar. The right post valve should be used on your right side, and the left post valve should be used on your left side.

Positioning the right and left cylinders on your body

Positioning your cylinders correctly on your body is essential for good streamlining, good kicking technique, ease of use, and safety. The drawing below illustrates the proper angle of the cylinder on/off knob and the brass clip in conjunction with the front and back of your body. The drawing also illustrates the proper positioning of the cam buckle and added weight. The first stage regulators should be tilted slightly towards your front. All hoses, if possible, should be routed down towards your front. Make sure the HP gauge is located so that it can be read during the dive.
Note: The cam strap buckle and weight should be positioned between the diver and the cylinder to help reduce the chance of a line snag.


Hose configuration and placement

Proper regulator hose configuration and placement is also essential for safety, ease of use, streamlining, and access. The diagram below illustrates the proper hose placement for side mount cylinders. A long hose can be used on the left cylinder if desired and pulled up and around the back of your neck.
Ninety-degree elbow adapters can be used on the second stage regulators to prevent jaw fatigue from sharp hose angles.
Custom length hoses for the LP inflators and regulators can be designed to further streamline and simplify the system. Loose hoses should be tucked under the waist belt to further streamline your rig.
The second stage regulator that is not in use should be clipped to the upper left D-ring. When changing second stages underwater, unclip the regulator not in use, exchange, and then clip the exchanged regulator back onto the left upper D-ring.

New Mexico Tech Professor Dr. John Wilson

SOCORRO, N.M. December 19, 2012– New research by New Mexico Tech professor Dr. John Wilson and doctoral student Katrina Koski sheds new light on the transfer of groundwater between very fast flow paths within karst rock formations and the much larger volume of karst rock with slow flow, with implications for water chemistry and contaminant behavior.
 koski edit in-scuba-gear
 Tech doctoral student Katrina Koski prepares to scuba dive into a karst formation. Their research will help describe how groundwater is transported through subterranean systems. Photo by Tanja Pietrass
 
 wilson in scuba-gear
 New Mexico Tech professor John Wilson suits up for a dive in Eagles Nest Cave in the Chassahowitzka Wildlife Management Area in Florida. Photo by Katrina Koski
 
Using funding from the New Mexico Water Resource Research Institute, Wilson and Koski conducted two-dimensional computer modeling to predict how water is transported through subterranean systems and what factors influence the rate and direction of flow.
This project, titled “Computational Fluid Dynamics Modeling of Karst Conduit-Matrix Exchanges with Relevance in Contaminant Transport, and Chemical Reactions,” has laid the groundwork for future field studies, which recently received funding from the National Science Foundation (NSF) and the U.S. Environmental Protection Agency (EPA).
Karst is a geological term that refers to underground formations that resemble Swiss cheese. On a large scale, we refer to karst features as caves or caverns. Generally speaking, karst refers to regions where rock has begun to dissolve chemically or “undergone chemical dissolution.” Karst aquifers are important water sources; they supply water to 25 percent of the United States, and some regions rely almost entirely on such formations; Florida, as an example, gets 90 percent of its water from karst. Also, much of the southern New Mexico Pecos Watershed is karst.
Wilson’s work examines the “hyporheic zone,” which is the area where water flows back and forth from the cave – or conduit – to the karstic rock formations – or matrix. Hyporheic zones and hyporheic flow was first characterized by biologists studying streams where surface water descends underground and later reappears in the stream. Chemists soon started examining surface hyporheic zones to explain what happens to dissolved solid organics (and other chemicals) as they move through hyporheic zones, as well as looking at how aquifer water mixes with surface water. Now, hydrologists like Wilson and Koski are breaking ground on subterranean hyporheic zones. In fact, Wilson was the first hydrologist to suggest that hyporheic zones could exist at the margin of a karst conduit.
“If water stays only a short time, it’s hyporheic flow,” Wilson said. “Through modeling, we are showing the propensity for deep flow. One interesting finding is how the variation in the karst wall topography impacts hyporheic flow.”
Scallops – or patterned undulations in the cave walls – create eddies in the flow, and hyporheic flows. Many karst conduits are air-filled with a riverlike flow at the bottom. This project specifically examines conduits that are completely filled with water. In some cases, given the right pressure, water can even flow upward through the cave roof into the matrix.
koski-graphics-ceiling for Cathy
  This simulation depicts a cross-section of flow in a karst conduit and induced hyporheic flow in the surrounding rock matrix that is located both above and below the conduit. The ceiling above the conduit has two large cupolas while the floor is lined with regularly-spaced features called scallops. The upper left (a) depicts relative flow speed (red= fast, blue = slow) with different color scales in conduit and matrix. The upper right depicts the distribution of fluid pressure (color, ed= high, blue = low), fluid velocity (arrows), and flow paths in the matrix. The ceiling morphology drives the hyporheic flow deeper into the matrix ceiling above the conduit than the smaller scallops drive flow into the matrix below the floor. With a porous and morphologically complex ceiling and floor, there is an interaction between the floor and ceiling morphology that creates nested hyporheic flow paths in the matrix on the other side of the conduit. The relative age of hyporheic flow is shown in the lower left (color: red= old, blue = new) while in the lower right is the highly variable spatial pattern of relative residence time for the returning hyporheic floor to the conduit from the ceiling (top) and floor (bottom). The illustrated domain is 2m wide and 2.5m tall.
 
Karst conduits typically have porous and permeable walls. Conduits range in size from building-sized to conduits too small for a diver. Water follows flowlines from high pressure to low pressure. For instance, a flooding event creates high-pressure in the conduit, forcing flow into the matrix. Water tends to flow quickly through the karst conduit and slowly through the matrix – or the aquifer. Conduits respond quickly to precipitation, while aquifers respond – or recharge – very slowly in response to rainfall.
In their modeling, Wilson and Koski accounted for the various characteristics of the karst conduit and the rock matrix, varying water pressures, conduit geometries and fl ow rates. They also applied standard physics models that describe flow rate – like Darcy’s Law and the Navier Stokes Equations.
The resulting models show water flow paths in conduit and matrix, as well as the travel time through the hyporheic zone.
As the project’s title suggests, Wilson’s WRRI research examines water chemistry and the transport of contaminants. They considered how groundwater in the karst aquifers changes chemically as it is transported through conduits and matrix.
Groundwater contains varying levels of organic and inorganic chemicals – both natural and anthropogenic.
As water moves through a hyporheic zone, dissolved chemicals undergo reduction-oxidation – or redox reactions. Water will enter the matrix in one chemical state, travel through the hyporheic zone and return to the conduit in a different state. Wilson and Koski’s models show that water entering the matrix at Point A may stay sequestered longer than water entering at Point B. The longer water is sequestered, the more redox reactions take place.
“We know the chemical reactions taking place,” Wilson said. “There’s a cascade of reactions as the water moves through the matrix. We are looking at how water gets sequestered, and how it is transformed into something less mobile and less toxic.”
In the absence of sunlight and biological factors found on the surface, water becomes anaerobic and then begins to lose other elements. At some locations where long-sequestered water re-enters the conduit, researchers are even finding mineral deposits.
Wilson and Koski are examining these chemical changes that occur in the water. Additionally, the researchers also look at speleogenesis – or cave formation. They are looking at the chemical reactions that cause the karst rock, which can be almost spongy, to disintegrate over time.
“Rock will basically dissolve from the inside-out,” Wilson said. “It’s rotting at depth. We can see the reactions and the enlargement of karst features.”
The next step in the research of karst hyporheic flow and water chemistry will be field studies. Wilson and Koski are working on a field study in Wakulla, Florida, near Tallahassee. Using a $387,000 grant from the NSF, they will scuba dive into the karst terrain. (Actually, they will hire NSF-approved divers because the target location is both deep and difficult to dive.) They will take core samples and install sondes that will measure and transmit data on water pressure, temperature and chemistry. The array of instruments will be the first such observatory dedicated to the study of hyporheic flow and chemistry. Koski, who earned her master’s at New Mexico Tech in 2000, will use that field work for her doctoral dissertation.
“We were selecting an important scientific question for the dissertation, one that had not been answered before,” Wilson said. “Katrina wanted to do her Ph.D. in flowing caves. I’d been doing research in air-filled caves and how gasses exchange. I thought her proposal was interesting.”
Koski also landed an EPA Star Fellowship to support her work. The Fellowship, which includes a stipend for Koski, allowed Koski’s salary from the NSF grant to fund another graduate student, Kenneth Salaz, who originally earned his bachelor’s at New Mexico Tech in 1998 and was Tech’s top undergraduate student that year, earning him the coveted Brown Medal.
“That’s the really nice thing about this WRRI grant,” Wilson said. “It has seeded two new sources of funding that are continuing today.”
– NMT –
By Thomas Guengerich/New Mexico Tech
This article was written for the Water Resource Reseach Institute's newsletter, The Divining Rod, and will appear in the upcoming issue.