AbstractCaves are the alpha and omega of all of ecosystems. It is where humanity first took refuge from the elements, and began its rise up to the great societies that now populate the earth. Like the Neanderthal, clinging to Gibraltar, caves may also be our only refuge from future events. This fragile, yet persistent, and constantly evolving ecosystem directly influences many basic human needs. However, population pressures, and human mistreatment through misunderstanding are putting a strain on this natural resource. Damage to these systems can be irreversible, and the scope felt through all systems. Caves and other karst terrain are extremely sensitive to outside influences, as well as changes in climate, and can be keen indicators of changes in environmental conditions on the surface of the earth. They are a little recognized, but essential aspect of continued human existence and it is imperative that appropriate conservation efforts actually preserve this resource, not just conserve it.
The Cave Environment
The underground chambers found within the earth form in various ways. While there are some similarities in geology and biology, caves sometimes host their own unique ecosystem. The one characteristic that they all share is in their formation, which is dependent upon not just hydrology, but also the chemistry of the internal and surface environment. As water travels through atmosphere, and percolates down through the layers of soil, it absorbs carbon dioxide (CO2), making it slightly acidic. As it works its way through fractures in the rock layers below the soil, it begins to dissolve certain types of rock, like limestone, and the cave begins to form. CO2 is not the only substance that water picks up in its journey through this system, towards its base line, which is typically sea level, or the level of the surrounding aquifer.1
While the soil above does filter out some substances, high concentrations of any one substance can enter a cave system and permanently alter its environment. Evidence of this appears in the various formations typically found in caves. Stalactites, stalagmites, columns, and flowstones form from calcite precipitated by evaporation of water with high concentrations of calcium and bicarbonates. Recent breakthroughs in molecular technology have shown that bacteria and various other microorganisms are also contributors to this process. In Lower Kane Cave, Wyoming, bacteria produce sulfuric acid that dissolves the rock, producing pockets in the rock, where other microorganisms attached themselves. Some of these microorganisms can also promote calcium carbonate precipitation, which further dissolves surrounding rock.2
These recent discoveries have awakened researchers to the potential of external influences on these systems. Certain bacteria and fungi that are not normally present within caves can continue their existence there, if accidentally introduced. Escherichia coli (E. coli), normally found in the digestive tract and feces of warm-blooded animals, can survive and in some instances intensify. E. coli is just one of several bacteria considered Human Indicator Bacteria (HIB), bacteria resulting from human contact, or contact with processes, which have been in contact with humans. Its introduction into a cave system can permanently alter the environment and crowd out other usual types of bacteria, which other life within the cave depend upon for survival.3
Cave Populations
The inhabitants of the cave that rely upon naturally occurring bacteria and funguses are troglobites and troglophiles. Troglobites live their entire life cycle in the cave, while troglophiles may also exists outside the cave, in the soil or under rocks. The species consists of a myriad of mites, spiders, worms, blind salamanders, and eyeless fish. They survive on stagnant, low-oxygen air for months on end, thanks to an extremely slow metabolism. Loss of vision aids in this precarious struggle for survival; many troglobites have supersensitive nerve centers that can detect the slightest change in air-pressure or temperature. These things are not enough to survive life in the cave; more often than not, troglobites have no other source of food, but one another. This is not surprising in an environment containing an unusual overabundance of predators and scavengers.4
Feeding only on what trickles down, and the other species that have fed on the same substance and one another, species often suffer the effects of biomagnifications and bioaccumulation. One of the most these type of common troglobite/troglophiles is the Springtail, a tiny insect about 2 mm in size. The Springtail feeds on bacteria and funguses found among organic litter within the cave and consequently, are very susceptible to HIB, which is perhaps the reason that the Fountain Cave Springtail (Pseudosinella Fonsa) is “G2 imperiled,” which means that there are only 20 possible sites throughout the world, where they exist, and only in caves with very limited human activity.5
Another troglobite in peril from human activity is the cavefish. In Cave Springs Cave, Arkansas, there has been a 30% decline in the cavefish populations, attributed to infiltration of Di (2-ethylhexyl) phthalate (DEHP), used primarily in the production of poly-vinyl chloride (PVC). This material accumulates in the soft tissue of fish and causes reproductive damage and reduced fertility. Upon investigating the source of this pollutant, resident crayfish were to found to contain significant concentrations of the compound; additionally, high concentrations of nitrite, total coliform and E. coli further suggested that bacteria from leaking septic systems or direction application of animal waste as fertilizer to the land above, was having an extremely negative impact on the entire system. As the primary source of food for the cavefish, it is easy to ascertain the cause of the reduction in associated populations.6
Mercury (Hg) and Monomethylmercury (MeHg) are also a huge concern for cave systems. These elements are naturally occurring, but human activity has created a toxic overabundance of these materials, due to atmospheric emissions from coal-fired power plants, as well as negligent methods of industrial waste disposal. Limited exposure can be damaging enough; however, long-term exposure to these elements produces damage to the heart, lung, kidneys, reproductive systems, and neurological disorders. One study done to measure the quantities of these substances in Mammoth Cave, Kentucky, revealed frightening results. Bat guano sampled from beneath gray bat colonies contained quantities of Hg and MeHg sufficient to produce adverse effects in humans.7
Bat colonies can be an early indicator of trouble beneath the surface. They belong to the group of cave residents referred to as the Trogloxene, organisms that use caves, but do not necessarily complete their life cycle there; other trogloxenes include cave crickets, ants, wood rats, and bears. Influenced by conditions within the cave, the lifestyle of the trogloxene also influences conditions within the cave. Wherever they roost, their dung, guano covers the floor of the cave, sometimes in enormous piles, and is home and sustenance to a variety of cave flora and fauna. If the bat dung diminishes, or becomes contaminated, the entire system is affected.9
Insectivorous bats are the most common, and feed on the variety of insects found along rivers and lakes; consequently, they are extremely susceptible to biological amplification of substances like pesticides. Populations of the Mexican Free-Tailed bats declined dramatically, from 8.7 million in 1936 to only 200,000 in 1973 primarily from the use of the pesticide dichlorodiphenyltrichloroethane (DDT), used extensively on cotton in the nearby Pecos River Valley. Numbers remain low to this day, likely due to the persistent use of DDT in Mexico. Dieldrin, a chlorinated hydrocarbon insecticide, and neurotoxin metabolite of Aldrin, an organo-chlorine insecticide, destroyed two maternity populations of gray bat in Missouri during the late 1970s. Originally developed as an alternative to DDT, Aldrin proved an extremely persistent organic pollutant that does not break down, and biomagnifies along the food chain. At least three other caves in Missouri have lost gray bat colonies after the use of this pesticide. The effectiveness of this pesticide is so good that in one instance local public health authorities in Panama used the substance to fumigate a cave intentionally, to remove bat colonies.10
Massive disruption of the food chain, sometimes wiping out an entire cave ecosystem, is the result of the use pesticides and herbicides. Nutrients are sparse within a cave. There are extraordinarily few organisms perceived to be plants; fungi and mold are the primary organisms at work in this place that sees little to no sunlight. In this system, anything with any nutritional value is fair game. The dung pile beneath colonies is the richest in nutrients. Primarily composed of insect matter, it can also contain pollen and other organic substances.11 The dung pile within a cave also contains decaying matter, originating from within the cave. Bats, snakes, trapped animals, and other organisms may fall, die, and decay in the dung pile. All of these elements go in to producing a plethora of nutrients for the bacteria, mold, and fungi that grow in this massive heap of decaying matter, which provides home to and feeds the troglobites and troglophiles. Humans also use guano, because it has such a high concentration of nitrates, and is excellent fertilizer. As has been demonstrated, this fertilizer also contains various levels of other less desirable substances that have infiltrated not just the digestive tract of the bats and other organism, but anything else that has infiltrated the confinement of the dung pile.
Caves and the Human Factor
The most dramatic effects are those imposed by humans and are the biggest threat to the biodiversity of caves. William Elliott, one of the most respected cave biologists in the United States, identifies the most significant human pressures on cave life as; “1) hydrological threats, 2) land development, 3) killing, over-collecting, and disturbing bats and other species, 4) sedimentation and contaminants, and 5) nutrient loss and enrichments.”10
Hydrological threats include damming, changes in drainage patterns due to development in drainage basins, and over-pumping of aquifers. Obviously, damming causes the inundation of some caves. Appropriate precautions, prior to inundation, preserves and protects endangered species from extinction. Banksula melones was rescued and transplanted to a nearby mine in the 1970s, when one of only two known habitats for this troglobite was inundated by the construction of the New Melones Reservoir on the Stanislaus River in California. Development near and in drainage basins decrease the quality of water in caves too. A 1990 study at Mammoth Cave National Park demonstrated a strong correlation between water quality and surrounding agricultural use, urban influences, and oil and gas exploration. Water exploration is another contributing factor. In portions of the southwestern United States, extensive groundwater pumping has caused the water levels of many aquifers to recede, past their ability to recharge. In Texas, over-pumping is causing spring failures and encroachment of salt water in to the system, which translates to death for many cave species dependant upon fresh water, including five currently endangered.
Land development factors have adverse effects on cave life, especially when done without appropriate planning. In a recently discovered cave beneath Georgetown, Texas, areas below the slab foundations of houses eliminated moisture and growth of any species of fauna. Fortunately, many species found refuge in passageways that were under the street and yards, which received water from leaking street gutters and lawn irrigation systems. Other development activities, such as tourism, quarrying, and mining can have negative consequences, as well. Opening a secondary entrance to Marshall Bat Cave in Texas to remove guano, the entire population of Mexican Free-Tail bats vacated, because meteorological conditions within the cave were no longer ideal. Without the bats, there was no more guano; cave systems lost their source of nutrients and human industry lost its source of capital.10 Onyx Cave in Missouri, recently witnessed the possible extinction of the Missouri Cave Lichen, a nutrient for many forms of cave bacteria, due to similar circumstances, when it became a tourist attraction in 1990.12
Nutrient losses have a profound effect on cave life, especially when contributed to by human activity. Citizens concerned about youth entering Shelta Cave in Alabama caused the evacuation of a large colony of gray bats, when they gated the entrance to the cave. Without the bats, there was no guano; nutrients levels dropped and aquatic systems within the cave dependant upon the guano decreased significantly. Meanwhile, continued development nearby caused the infiltration of the insecticide Heptachlor Epoxide. Likely used to treat nearby foundations, infiltration of this substance nearly decimated the Alabama Cave Shrimp population, resulting in its addition to the endangered species list in 1988.10
Nutrient loads in excess of the carrying capacity of the cave choke out life, while promoting the growth of more damaging organisms. Pig and cattle farms, fertilizers, herbicides, and pesticides threaten many cave water supplies, which are sometimes also the source of water for humans. Deep-well injection of wastewater and solid waste dumped in to dry caves near Mérida, Mexico resulted in an overabundance of cyanobacteria (blue-green algae), which contaminated the drinking water, affecting not only the local human population, but also the endangered jaguar and the threatened Morelet’s crocodile. Indiscriminate sewage disposal resulted in huge numbers of red tubificid worms, or “sewage fungus,” which nearly destroyed the troglobite community at Hidden River Cave in Kentucky.10 However, a new sewage treatment facility eliminated the flow of sewage in to the cave in 1989 and by 1995, the original community had reestablished itself and today, visitors enjoy ecological tours of the cave, demonstrating the effects.13
Chemical pollution is by far the most damaging to cave systems, and the most widely ignored, until recently. The most recognized poison to caves is carbide from acetylene lamps used by cavers through the 1960s. The calcium hydroxide in these spent carbide cartridges is highly toxic to cave fauna. Typically discarded or buried in caves, the toxin can leak in to the soil and water for hundreds of years. Modern technology has not improved the situation very much. Mercury used in batteries for cave lighting continues to be a concern for the cave environment, mostly due to accidental or careless action by individuals exploring caves.
Accidents are the dominant factor in cave pollution though. One of the most massive destructions of cave biota was only an accident. A pipeline break near Dry Fork Creek, Missouri dumped 80,000 gallons of ammonium nitrate and urea fertilizer in to Maramac Spring, the third largest in the state. 10,000 of the rare Salem Cave Crayfish and 1000 of the Southern Cavefish died because of elevated ammonium and nitrate nitrogen concentrations. Slower movement of toxins in the environment can have equally devastating effects. Leaking diesel fuel, from a service station storage tank, decimated the crustacean population of Wildcat Saltpeter Cave in Virginia.10
Human activities undoubtedly leave a mark on cave systems; the simple presence of a human can dramatically alter these fragile environments. Ignorance is most often a major contributing factor. Unfounded fear of vampire bats in Mexico has led to the destruction of many bat colonies in the country; indeed, the practice of extinguishing bat colonies in Central and South America continues even today. Science has also contributed to the decline of certain cave populations. One biologist, D.C. Culver admitted that his methods of collection had resulted in a severe decline in populations of cave isopods. Additionally, early attempts to track bats using banding caused torn wing membranes and injured their fragile bones, affecting their populations. Today, the preferred method of tracking uses tiny radio transmitters, glued to the fur, which has helped to provide a better understanding of bat habits, the factors that influence them, and their diminishing populations. It is extremely important to understand these factors too, because without the bat, there is no guano; in most instances, without guano, there is no cave life; without cave life, no organisms exist to help filter the water indicative of these environments, which humans depend greatly upon.10
The Solution for Caves
The most obvious solution is careful attention to all of the factors that can influence cave structures. There are many different theories on best practices. The most popular are: isolation, ecological surveys, cave gating, and restoration or transplantation of species, when possible.
Some perceive that isolation of cave and karst areas is the ultimate solution and can be in some instances. However, while this method of protection can aid to restore some level of normalcy to a cave, inattentiveness to contributing factors can further damage these systems. In one case, a quarry near Inner Space Cavern in Texas could be the cause of the destruction of several caves in the area, since 1963. While the caves are isolated, the quarry creates an artificial barrier to the natural flow of nutrients in the water supply to the caves, while causing excessive sediment deposition. As demonstrated previously, this can dramatically alter nutrient levels, which ultimately affects the biodiversity of the cave.10
Cave gating is an excellent way of preserving the ecosystems within, if special attention is devoted to ensuring that maximum levels of access are not inhibited. When designed properly, gates can protect cave resources and limit the ability of intruders to inflict damage, while at the same time permitting the various trogloxenes and troglophiles to move in and out of the cave, unimpeded. Unfortunately, improper gating can disrupt airflow, cause variations in nutrient levels, and sometimes inhibit the free movement of creatures dependent upon the entrance of the cave.14 However, even the most perfectly planned gate will have unintended effects. Extremely particular about obstructions in the openings of their caves, in certain instances gray bat colonies have evacuated even the most appropriately gated cave. With so very few caves suited to hosting this endangered species, even the most careful attention could induce a massive decline in population.
Removing trash and other materials not normally found in caves can help in restoring the ecology; however, care not to remove items that might cause excessive stress in the cave community, is extremely important. Rotting wood sometimes infiltrate the environment of the cave. While not normally found there, when it is, large populations of cave invertebrates take advantage of the decaying matter. Removing the wood suddenly could wipe out an entire species, while gradual removal permits these creatures to take refuge in other parts of the cave. Foreign algae and moss growing on cave features can be eliminated using special bleach solutions, though as with many other chemicals, can be disruptive to other organisms.10
One of the most experimental concepts in cave preservation is ecological transplantation. As previously mentioned, this method did rescue a species of cave life, threatened by inundation by the New Melones Reservoir. However, transplanting sensitive and sometimes endangered cave species, which rely heavily on specific environmental conditions, is probably a good emergency measure at best. Caves have their own natural community. If the species introduced does not already exist there, is the relocation effort sustainable? If the effort is sustainable, the species will be in peril from competition within the existing ecosystem. Even if all of these efforts are sustainable, and the species is able to persist, alterations to the two communities may irreversible. In the case of McLean’s Cave, at the New Melones Reservoir, other problems have recently presented themselves. The mine requires a regular stock of wood to maintain the appropriate level of nutrients, for the species transplanted there. Additionally, a lack of commitment in funding for long-term monitoring, could ultimately lead to neglect of the transplanted species. Ironically and fortunately, after the relocation of this species, researchers discovered 18 caves in the area containing the same species previously thought endangered.10
Landowners are the primary protectors of caves though and help and support is readily available through local conservation agencies. Immediate solutions for landowners actually cost very little and are rather simple practices to implement. Preserve wooded areas around caves and maintain a forest path 100 feet wide to, and along local streams for bats and other trogloxene. Owners should deny access to caves during the bats summer roost, as well as during their winter hibernacula. Avoid burning any sort of material near the cave entrance, and most importantly, eliminate or reduce the potential for infiltration of compounds easily dissolved in the soil and water. (MoDoC)
With so many species influenced by all of the processes of the earth, living within these formations on earth, it is essential that caves remain protected. Damage to these systems can have a wide impact on nearly every aspect of human life. Contamination of caves leads to the contamination of any species dependent upon the life that the cave nurtures, as well as those elements that are only passing visitors to the cave, like water. In the United States, caves and karst formations influence nearly 25% of the drinking water consumed. (Christopherson) If development continues with disregard for this system, the effects may not be immediately apparent; however, long-term repercussions over successive generations will be witnessed, and in certain instances, may be unrecoverable.
References
- Plummer, Charles C Plummer & McGeary, Effects of Ground-Water Action on Caves, Sinkholes, and Karst Topography. Physical Geology, 3rd Ed. Dubuque: William C. Brown Publishers, 1985. 222-223
- Barton, Hazel A. Barton & Northup, Diana E. Geomicrobiology in cave environments: Past, Current, and Future Perspectives. Journal of Cave and Karst Studes, v.69, no 1; [article online] 2007. http://www.caves.org/pub/journal/PDF/v69/cave-69-01-163.pdf . 163-178.
- Lavoie, Kathleen H. Lavoie & Northup, Diana E. Northup. Bacteria as Indicators of Human Impact on Caves. National Cave and Karst Management Symposium. [article online] 2005. http://www.nckms.org/2005/pdf/Papers/lavoie-bacteria.pdf
- Krajick, Kevin, “Discoveries in the Dark,” National Geographic. [article online] 2007. http://ngm.nationalgeographic.com/2007/09/new-troglobites/new-troglobites-text
- Lewis, Julian J. Lewis. Conservation Assessment for Fountain Cave Springtail (Pseudosinella Fonsa). USDA Forest Service, Eastern Region [article online] 2002. http://www.fs.fed.us/r9/wildlife/tes/ca-overview/docs/insect_Pseudosinella_fonsa-FountainCaveSpringtail.pdf
- Brown, Arthur V., Graening, G.O., & Vendrell, Paul Vendrell. Monitoring Cavefish Population and Environmental Quality in Cave Springs Cave, Akransas. Arkansas Water Resources Center Publication No. MSC-214. [article online] 1998. http://www.uark.edu/depts/ecology/docs/ANHC1999Report.PDF
- Helf, Kurt Lewis Helf. Mercury and Methylmercury in the South Central Kentucky Karst: Its Transportation, Accumulation, and Potential Effects on Vulnerable Biota. National Cave and Karst Management Symposium [article online] 2003 http://www.nckms.org/2003/pdf/HELF.pdf
- O’Shea, T.J. & Botan, M.A. Monitoring Trends in Bat Populations of the United States and Territories: Problems and Prospects. USGS Information and Technology Report USGS/BRD/ITR—2003-0003 [article online]. 2003. http://www.caves.org/pub/journal/PDF/V66/v66n3-Book_Reviews.pdf
- Baker, Gretchen. Field Guide to Cave Life. A Guide to Cave Life in Great Basin National Park. [article online] 2008. http://www.nps.gov/grba/naturescience/upload/Field%20Guide%20to%20Cave%20Life.pdf
- Elliott, William R. Conservation of the North American Cave and Karst Biota. An electronic preprint from Elsevier Science’s Subterranean Biota [article online] 1998 http://www.utexas.edu/tmm/sponsored_sites/biospeleology/preprint.htm
- Darntan, Michael. Making a Study of Bat Droppings. Microscopy UK [article online] 1995. http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artapr99/bdbat.html
- Low, Jim. Species of Concern: Missouri Cave Lichen. Missouri Conservationist; 2009
- Lynn, Jessica. Kentucky Cave Restored: Hidden River Cave and American Cave Museum. Associated Content [article online] 2007 http://www.associatedcontent.com/article/316671/kentucky_cave_restored_hidden_river.html
- Roebuck, Brian, Vakili, Ahmad & Roebuck, Lynn. Cave Gate Airflow Disturbance – A Qualitative Study. National Cave and Karst Management Symposium. [article online] 1999. http://www.nckms.org/pdf/roebuck.pdf
- Care and Maintenance of Missouri Bat Caves. Missouri Department of Conservation [article online] 2004. http://mdc.mo.gov/nathis/mammals/batcave/
- Christopherson, Robert W. Karst Topography and Landscapes. Geosystems, 6th ed. New Jersey: Pearson/Prentice Hall; 2006. 412-418