Definition

There are many archaeological sites in wetland areas, but to be included in a category labeled ‘waterlogged’, a site cannot have undergone any drying episode throughout the time period of its existence. When dried, the fragile organic component disintegrates, sometimes in a matter of hours. Degradation is particularly deleterious for botanical specimens.

The survival of organic materials entombed in a waterlogged context can be attributed to anaerobic (oxygen-free) conditions that inhibit or minimize activities of aerobic (oxygen-requiring) bacteria (Figure 1). There are, however, microorganisms that exist in anaerobic or poorly oxidized environments that can eventually destroy 95% of the carbohydrates (cellulose and hemicellulose) of plants leaving only a skeleton of lignin, which most bacteria cannot digest. The voids left by the removal of cellulose and hemicellulose are replaced by water. The reason that objects disintegrate rapidly when a waterlogged environment becomes desiccated, or when items are removed from their protective matrix, is because the water within the voids evaporates and the cellular structure collapses. When the moisture content of a waterlogged deposit or a waterlogged item falls below a certain percentage, the process is irreversible; that is, no amount of rewetting will undo the damage. Wood, for example, shrinks, splinters, and warps, and its former shape is no longer recognizable.

The fact that the survival of waterlogged materials depends upon interment in oxygen-free conditions has An unfortunate consequence: the objects are invisible until accidentally discovered as a result of erosion or economic pursuits. Severe damage often occurs to specimens and sites before their significance is recognized.