The author's previous notes on this topic is: A preliminary look at the ciliates of sinkhole #25.

I had a recent opportunity to return to Bitter Lake National Wildlife Refuge near Roswell, Chaves county, New Mexico, and thus collected water samples from not just Sinkhole #25 as I had earlier, but also from Sinkhole #20 only about 30 or so meters to the northeast of Sinkhole #25. To this I added a third sample from an overflow pond south of Bitter Lake itself. The two sinkholes differ quite a bit in size and characteristics despite their close proximity. Sinkhole #25 has no fish in it, but sinkhole #20 does. Large clumps of Chara nearly fill sinkhole #25, but there is much more clear surface on the much larger (and possibly deeper) Sinkhole #20. Sinkhole #25 had many aquatic insects such as notonectid, corixid and giant water bugs, dyticid and hydrophilid beetles and damselfly larvae, as well as many amphipods. Sinkhole # 20 had recently undergone a huge emergence of dragonflies, especially the seaside dragonlet and on both my trips was the only place where we collected haliplid beetles. The overflow pond was quite different from both sinkholes in that it was smaller yet and even more highly salty and alkaline. It was the only site where we found saldid shore bugs (genus Pentacora) and the black and white patterned tiger beetle Cicindela hemorrhagica. The muddy shore was heavily infused by slime indicating algal and bacterial blooms. As it turned out I might as well have taken samples from the ends of the earth as the samples, while exhibiting some similarities, were each characterized by their own constellation of dominant organisms.

The physical characteristics of the sinkholes from 2002-2004 varied considerably. Sinkhole # 20 had salinity and pH readings of 8.6 ppt, pH 8.9 (Winter 2002); 8.1 ppt, pH 8.6 (Summer 2002); 8.8 ppt, pH 8.39 (Summer 2003), 8.4 ppt, no pH taken (Summer 2004). Sinkhole # 25 had salinity and pH readings of 17.4 ppt, pH 8.5 (Winter 2002); 17.0 ppt, pH 9.0 (Summer 2002); 19.6 ppt, pH 8.07 (Summer 2003), 13.9 ppt, no pH taken (Summer 2004). Bitter Lake itself had salinity readings (no pH taken) of 22.8 ppt (01/02), 124 ppt (08/02), 8.2 ppt (01/03), 28 ppt (07/03), 30 ppt (01/04), and 29 ppt (07/04). The wide swings in Bitter Lake salinity are dependent on rain or lack thereof of, which alternately dilute and concentrate the level of salinity in this shallow lake. The overflow pond that I sampled should have similar wide swings as it is in essence a finger of the playa lake.

The highly variable conditions at Bitter Lake and its sinkholes allow for a huge amount of diversity in the biota. In recent times the number of known dragonfly and damselfly species has risen from 90 to over a hundred! Collections that we have made there over four half days of work resulted in over 500 specimens of 200 species of arthropods. The species in the microbiota are largely unknown, but are certain to be quite diverse. The observations I have made are only preliminary, but give at least an impression of this impressive diversity.

Overflow pond from Bitter Lake (Bitter Lake in background) (Photo by C. S. Bundy)

The results of my rather incomplete survey were none the less quite interesting. I summarized the comparison of the three samples in the following table. It might be noted that the water smelled somewhat sulfurous, especially after ten days!

Table 1. Micro-organism differences and similarities in samples taken from three different bodies of water at Bitter Lake National Wildlife Refuge on July 21, 2004. Observed July 24, 2004.

Table 2. Micro-organism differences and similarities in samples taken from three different bodies of water at Bitter Lake National Wildlife Refuge on July 21, 2004. Observed Aug 1, 2004.

In actuality the diatom flora was more varied than these tables would indicate. The species ranged from relatively tiny needle-like species to the huge Synedra, looking like chemical stirring rods. Some of the boat-like naviculoid types were motile, moving slowly across the field. I suspect that although naviculoid diatoms were found in all samples, they may not have been the same species or even genera in some cases, as between the sinkholes and the very saline overflow pond. In essence there appeared to be at least ten species of diatoms between all the samples, with a few dominating. It was especially interesting that the overflow pond was the only place dominated by Synedra. The density of diatoms also varied, with the Synedra rods in the overflow pond much more numerous than any type in any of the other samples.

The ciliates were also quite interesting, but I was only able to identify one genus for sure, Metopus, which showed up in the samples from Sinkhole #25 after ten days of collection. These strange ciliates were oddly twisted, but otherwise very flat, and as they moved in their characteristic half rotation and back, their aspects changed considerably. Many smaller ciliates were seen, but none were easy to place.

The bacteria seen in these samples were of basically two types, tiny (just visible at 200X) short bacillus-like rods and much larger (to over 100 μm) watch spring-like spirochetes. The later were motile. I also saw strange motile hair-like organisms about the same size that I could not place to even kingdom (if any body has any ideas I would appreciate them). They were much too thin to have been any nematodes that I have ever seen. Finally, there were round clusters of vibrating tiny (less than 5 μm) protoctists (flagellates?) through which medium-sized ciliates moved, possibly eating some of the members of these “schools.”

All in all I think the bodies of water on Bitter Lake National Wildlife Reserve could easily serve as projects for years. I have not included the other sinkholes, springs, the main playa lake or the Pecos River. Each of these may well have differing communities of microorganisms. A few may even be associated with the endangered species of spring snails or amphipods that live in some sites. I had no permission to sample these sites and so did not. The pH and salinity varies even more than among the three sources I sampled. My guess is that there may well be hundreds or even thousands of species involved and numerous specialized ecosystems.

I offer my thanks to the officials at Bitter Lake National Wildlife Refuge, who allowed me access to the sinkholes and overflow pond, and especially to the refuge biologist, Gordon Warrick, who guided me to sink holes #20 and #25 and graciously provided me with pH and salinity records for the sinkholes and Bitter Lake itself.

I would be happy to hear of anyone who has looked at similar ecosystem microorganisms.

Comments to the author, David Richman, are welcomed.

Protozoan references used were:

Patterson, D. J. 1998. Free-Living Freshwater Protozoa: A Colour Guide, John Wiley and Sons, New York. Kudo, R. R. 1966. Protozology, 5^th ed., Charles C. Thomas Pub., Springfield, IL.
Jahn, T. L., E. C. Bovee and F. F. Jahn. 1979. How To Know the Protozoa, 2^nd ed., William C. Brown, Dubuque, IA.

Diatom references used were:

Vinyard, W. C. 1979. Diatoms of North America. Mad River Press, Eureka, CA.
Wehr, J. D., and R. G. Sheath. 2003. Freshwater Algae of North America: Ecology and Classification. Academic Press. Amsterdam.
Footnote 1: The salinity measurements quoted are in parts per thousand (ppt).
Footnote 2: The author used 100-200x magnification and phase contrast for his observations.

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