Degradation of wood buried in soils exposed to artificially lowered groundwater levels in a laboratory setting

Service life of wooden foundation piles could be at risk during modern urban construction work, as local groundwater conditions might change and cause increased degradation of nearby buried wood material. Maintaining a high groundwater level has been linked to good preservation conditions, but detailed studies on the effect of lowering the water level have not yet been performed. In this unique designed laboratory study, we explore how reduced water levels affect degradation rates of wood rods embedded in clay soil. In clay columns, effects of reduced water levels (30 cm, 60 cm) and fluctuating water levels (0–60 cm) were investigated at three levels (−5 cm, −30 cm, −55 cm). Two controls were included, one with no water reduction and one with sand soil. Redox potential was measured regularly at the three levels, and soil moisture was measured at start and end of experiment (12 months). Results showed that lowering water levels generally increased wood degradation. Decay took place almost exclusively by soft rot fungi and was highest at −5 cm below soil surface. At −55 cm depth and −400 mV redox potential, scarcely any decay was observed. Desiccation was highest in sand and in clay with −60 cm water reduction, and any decay process here had stopped. Surprisingly, fluctuating water level generated equally low decay rates as a high stable water level. Covered soil surfaces yielded less degradation and the effect was even comparable to that of a maintained high groundwater level. Protecting soils against desiccation could thus keep wood degradation at a minimum at open-air excavations. More experiments are needed to determine long-term effects and threshold values for decay in relation to redox potential.