Although the study of fen and bog lands probably doesn't sound extremely captivating, it is important to discuss a few of the physical and chemical properties of these environments in order to fully understand how they so effectively preserve bodies and artifacts.
Fens and bogs are waterlogged habitats found extensively in Europe. Walking on a bog entails stepping on a "living carpet" of moss which floats on a slightly acidic material composed mostly of water held in by fragments of Sphagnum moss and peat. Bogs consist of two layers: a thin top layer, the acrotelm, through which water can move quite rapidly, and a thick amorphous layer of peat called the catotelm. Raised bogs may be only 2% peat and 98% water, while blanket bogs, which by weight are only 85% water, are the more solid of the two types. The catotelm environment stays amazingly constant, protected from any turbulent outside environmental changes by the acrotelm. Buried in these conditions, archaeological material can lie undisturbed for generations; however, the chemical content of bogs has just as important an effect on remains as the sheltered environment.
Sphagnum moss and peat harvested from bogs have traditionally been used to exploit their seemingly antimicrobial properties. In the past, sailors would often take bog water with them on sea-voyages since it stayed algae-free longer than well or spring water. Dried moss was used to bandage wounds extensively during World War I, as it has been used throughout the history of folk medicine. Horticulturists today value Sphagnum peat for its resistance to decomposition and ability to neutralize odor. Scientists have proposed several theories explaining these effects. Some believe that the moss releases a chemical called "sphagnol" similar to the decay-resisting fungicides released by junipers and cedars. Others propose that the acid in bog water combined with anaerobic conditions delays the formation of putrefactive bacteria; this acidity has also been cited as the cause of the extreme decalcification observed in most bog bodies. However, it is now believed that the low density of bacterial cells in Sphagnum peat bogs is due to deprivation of essential metal cations and amino-nitrogen, which are retained by a pectin-like substance called sphagnan in the cell walls of the moss (Painter, 1995). Muscle, tissue and wooden artifacts can only survive in the bogs because of the way this sphagnan immobilizes destructive bacteria. Sphagnan has also been attributed with tanning the bodies preserved in the bogs. Tanning implies the process by which hide converts into leather; when leather is tanned with sphagnan it becomes highly water-attractive, fat-repellent and turns the very dark coffee color exhibited by most recovered bodies (seen in the above picture of Tollund Man).
Not all bodies have been recovered in the same physical condition; in other words, they were not all preserved in exactly the same way. In some cases, all muscle and skin have long decayed, leaving only skeletons. Often the opposite occurs, and all bones have dissolved away leaving soft tissue and tanned skin. Scientists have a hard time explaining these discrepancies. Also, much to the dismay of forensic scientists and archaeologists alike, peat bogs seem to be detrimental to the preservation of such things as DNA. However, instead of citing all of the imperfections of bog preservation, it's much more productive to concentrate on its benefits-the scientific advances made possible through studying bog relics.