Depth of burial, an important factor in controlling bacterial decay of waterlogged archaeological poles

Wood discs from two waterlogged softwood poles were investigated for variations in bacterial decay. Exterior and interior degradation was observed using light, transmission and scanning electron microscopy. Maximum water content (Umax) was measured and extent of decay from the surface towards the wood interior was investigated. Despite a well preserved appearance, the majority of the tracheids were heavily degraded. Erosion bacteria were identified as the main degraders and a significant difference in degree of decay was found between the upper and lower parts of each pole. Small differences in oxygen concentration, derived from depth of burial, are suggested as the controlling factor. Active erosion bacterial decay was found in the inner parts of the 1200-year old wooden poles.