Long-term study on wood degradation in urban soil-water systems - implications for service life of historic foundation piles

Abstract

Many historic buildings in urban environments are raised on wooden foundations, and due to microbial degradation their service life varies greatly. This is one of the first field experiments in urban environments where wood decay is studied on proxy samples and related to ongoing processes in historic foundation piles. Here 90 proxy samples are exposed at 8 urban sites for 6, 12, and 18 months in the centre of Gothenburg. Development of microbial decay is followed in dipwells adjacent to well-studied historic piles. Analyses by light microscopy show that decay took place at all sites. Erosion bacteria were the sole degrader of wood at ¾ of the sites, both at groundwater level and at pile head level, indicating near anaerobic conditions in the soil pore water. At the two remaining sites, soft rot was also active. Decay increased over time and results demonstrate a significant correlation between depth of exposure below groundwater level and decrease in decay rates. Decay intensity varied between the sites, indicating that other site-specific conditions affect microbial activity. Redox and oxygen measurements did not show any correlation to observed decay intensity in proxy samples. Advise to stakeholders and for future studies are given.