Algae in Caves

Take a look at these two photographs and other than what they are pictures of see if you can see any major differences (Top picture from Carlsbad Caverns National Park [my post here] bottom picture from Mammoth Cave National Park [my post here]).

More photos from Carlsbad Caverns, more photos from Mammoth Cave.

What jumps out to me is the green stain on the wall in the picture from Mammoth Cave. This is something I really noticed while touring the cave and there was some really drastic growth on some of the walls in the New Entrance portion of the cave. According to Smith and Olson (2007) these are some of the 28 species of cyanobacteria, green algae, and/or diatoms. For the rest of this article I will refer to all of these groups as algae, because that is far easier than typing all those out every time. All of these groups are photosynthetic groups that need light as well as moisture to live and since they produce their own food they can grow on cave walls. Algae as well are known as pioneer species meaning, in this case, that they live on rocks, unlike plants which need soil to grow, and in the process they modify the rocks under them by producing weak acids during photosynthesis that break down the rocks they are on. On the surface where algae lives naturally this is a good thing, it is a form of chemical weathering that breaks the bonds that hold the rock together and forms soils in the long run, except in karst areas because it is hard to produce soil from limestone (not going to explain here if you want to know ask). In caves the algae are doing the same thing except that they naturally only occur where the sun shines so in order for them to grow deep down in caves is because we put lights down there.

So why so much more algae in Mammoth Cave than in Carlsbad Caverns? Some of it may have to do with the outside environments of the two areas. Carlsbad is in a desert and Mammoth Cave is in a temperate forest so it is going to be much more moist in Mammoth Cave. Carlsbad does, however, have algae that grows on the surface outside the cave. The main difference has to do with the type of lights that have been installed within the cave. Carlsbad Caverns has been moving toward lights that produce light at a wavelength that the algae cannot grow at (on a side note if you go to the link they talk about how they are changing the lights again and you can see some of that in my pictures). There is still some need to physically remove the algae as the Carlsbad website mentions:

Some of these algae live in the caves, too. Under normal light conditions, they will grow on walls or in pools as far into a cave as the sunlight penetrates (the twilight zone). In caves with artificial light sources of suitable wavelengths, such as Carlsbad Cavern, algae will grow in the dark zones near the lights. These algae are considered pest plants, and are kept under control periodically by park staff.

Smith and Olson (2007) point out that most of the work to remove the algae in Mammoth Cave has focused on physical removal using a weak sodium hypochlorite or bleach. This use of bleach can have physical effects on the cave but if the algae is not removed there can be other effects. Smith and Olson (2007) recommend the use of similar lights to what Carlsbad Caverns uses so the algae is unable to photosynthesize and therefore will not be able to produce food and will die without physical damage to the cave.

One other interesting thing the Smith and Olson (2007) paper is the only thing I can find about the removal of algae from Mammoth cave and they do not have anything about it on their website nor did they have any signs or did I hear from any of the rangers about it. Carlsbad on the other hand has the quote mentioned above and many of the rangers and signs throughout the cave mentioned the attempts to remove the algae. If I am wrong about this please let me know.

Source:
Smith, T. and R. Olson. 2007. A taxonomic survey of lamp flora (algae and cyanobacteria) in electrically lit passages within Mammoth Cave National Park, Kentucky. International Journal of Speleology. 36(2): 105-114.
(This source can be found here and is open access so the pdf is here)

Carlsbad Caverns National Park

Location: Eddy County in southeastern New Mexico right near the border with Texas, near Carlsbad, NM.

Introduction:
Within about 30 miles of Guadalupe Mountains National Park (Guads), Carlsbad Caverns National Park (Wikipedia page) is the first of the National Park cave systems that I visited. As with the Guads this national park is located in the high desert of the American Southwest. The surface footprint of the National Park is much greater that what would be expected if it was to just be the cave itself and as such there are many other activities to see and do including many great views as well as being able to visit other entrances to the cave system. If you are hitting up one of the two parks in the region you are doing something wrong since they are both so close and both offer many different options to explore.

Geology
As you might expect the geology of Carlsbad Caverns is very similar to that of the Guads so if you have not read my write up on that I suggest you do. A quick summary for those who have but may not remember it all. In the Permian the area that now includes Carlsbad Caverns and the Guadalupe Mountains was covered by a warm, shallow sea that allowed for the growth of organism that secreted calcium carbonate in a primarily sponge-reef. The sea eventually began to dry and covered up much of the reef in evaporites. Overtime these calcium carbonate rich rocks were lithified to form a large primarily limestone deposit. This limestone was eventually uplifted and formed the mountains and ridges in this area.

Now I can expand on something I mentioned in passing when I talked about the Guads is the formation of caves which this post will allow me to expand on. Caves form primarily in limestone rich areas which are typically known as karst areas, why? The answer is simply that limestone breaks down easily in acid rain. All rain has some acidic qualities in it these are picked up as the rain water passes through atmospheric CO2. When the CO2 is present in the atmosphere and gets taken up by water it forms carbonic acid but it is typically pretty weak in the rain water itself. As the rain water can either run off into rivers and lakes and eventually the ocean or it can penetrate the surface and reach the water table. As the water moves underground if it reaches a limestone rich deposit the carbonic acid will react with the limestone, this dissolves away a part of the limestone and releases CO2 back into the atmosphere. This dissolved water is part of the reason why people who have well water will get hard water stains etc a lot of times. Also of some interest this is another reason why scientist worry about excess CO2 in the atmosphere because it causes the oceans to become more acidic making it more difficult for calcite secreting organisms, coral etc, to secrete calcite and can cause them to actually dissolve over time, this is called ocean acidification. Over a long period of time the water can dissolve away large areas of the limestone and form caves and as the water table drops or the area with the cave is uplifted these caves become exposed at the surface where we find them. Another interesting thing that can happen is that the water can get supersaturated in lime at higher subsurface pressures and when this water reaches the surface, or a depressurized cave, it will drop this lime off and form a special kind of limestone called travertine. Travertine is what typically is found on the edges of cave walls as well as in many of the formations in the cave.

Animals have always played a large role in the environment of caves and the most typical animal that people think of with caves is bats. Carlsbad Caverns is no exception to this and during the summer you can watch the bats fly out of the cave at night, I hear this is an awesome sight but one which I have not yet seen. Other animals also use the caves and deep within the cave system it becomes an environment like no other. A karst system can form many openings into the cave system on the surface some of which may be nearly vertical or just impossible for a surface animal to escape from. This leads to the possibility of fossils being found in caves and in fact they have been found in this cave as well as others around the world. If you really wish to learn how these fossils may get preserved I recommend this post over at History of Geology, yes I know I have mentioned it before. I'm sure I am missing some aspects so if you have questions feel free to ask them in the comment section below and I will try to answer them.

More Pictures I have even more in the Carlsbad Caverns portion of my Flickr page.









Further Reading:

National Park Service's web page on the Geology and on the Caves

While only partially related: Bebout, D.G. and Kerans, C. 1993. Guide to the Permian Reef Geology Trail, McKittrick Canyon, Guadalupe Mountains National Park, West Texas. Bureau of Economic Geology, Austin, 48 p. (I really recommend this last one if you are going to do the geology trail (of the Guads) because it includes stops and talks about the geology of the are. A digital copy can be found here but I recommend buying one from the park when you get there [the Guads], support your parks!!!)

National Park Service Series homepage