Burial conditions and wood degradation at archaeological sites in the Netherlands

A series of waterlogged archaeological sites in the Netherlands were investigated to examine wood degradation by erosion bacteria. Chemical analyses of soil and water at the sites showed a large variation in burial conditions, reflecting differences in sediment composition, salinity, trophic levels, and past burial conditions. The most constant factor was the generally low redox state. Despite these large differences, degradation by erosion bacteria was found in all wood samples, indicating active degradation in a large number of different environments including reducing ones. The degree of degradation varied markedly, but showed no correlation with the chemical burial environment, although water movement may have had a role to play. As a result of degradation by erosion bacteria, wet wood is damaged easily and is also susceptible to damage and deformation during drying out. Sites where oxygen was available showed evidence of degradation by soft-rot fungi. Moreover, one marine site showed loss of wood strength that may be related to the oxidation of iron sulphides and the associated production of sulphuric acid. In situ protection of wood requires the maintenance or restoration of an oxygen-free burial environment, and decay by erosion bacteria may be slowed by reducing water flow at the site.