Changes in the properties of English oak wood (Quercus robur L.) as a result of remaining submerged in Baltic Sea waters for two years

• Samples of oak wood submerged for two years in Baltic Sea water were characterized.
• Properties of natural wood and wood submerged in the water were compared.
• Changes in chemical compounds of wood submerged in marine water were observed.
• Marine wood was more susceptible to rot caused by Trametes versicolor fungus.
• A decrease of physical and mechanical properties was noted.

The aim of the research was to determine the changes in the properties of oak wood caused by the submergence of samples in the Baltic Sea for two years in comparison with the properties of twin control samples which had not been submerged in sea water. Test samples of oak wood (250 × 10 × 10 mm) were placed in the waters of the Baltic Sea (near the wreck of the Swedish warship Solen). The samples taken out of the sea were examined visually and described. The changes in the physical, chemical and biological properties of the wood samples were investigated. The obtained results indicate noticeable, measurable changes in the oak wood submerged in the sea: 18–25% loss of wood mass, a decrease in bending strength and compression strength of up to 40–65% of the initial values. In addition, the following were noted: a clear change in wood colour and surface structure, an increase in the content of mineral substances, an increase in pH value, a decrease in the content of water-soluble substances and extractives (ethanol). The laboratory test with Basidiomycetes fungi has showed that wood became significantly more susceptible to the white-rot caused by Trametes versicolor than to brown-rot caused by Coniophora puteana fungus. Further observation of the noted changes may be useful for the protection and monitoring of underwater archaeological objects.