Studying bacterial wood decay under low oxygen conditions—results of microcosm experiments

In recent years various studies have indicated that bacterial wood attack can cause considerable strength loss of waterlogged pile foundations in unexpectedly short periods of time. In this study we set up microcosm experiments with pine sticks placed in waterlogged sediment to establish, monitor, and manipulate the bacterial wood decay process. Microcosms were equipped with oxygen sensors (optodes) and CO2, CH4, and N2O head space measurement devices. Microcosm head space was aerated with air, air+O2, N2, air+water circulation and sediments were supplied with NO−3, NH+4, PO3−4, SO2−4, and glucose. Wood decay was microscopically detected and classified for low decay intensities, and was found to have occurred in all treatments after 150 days. The fastest rate of decay developed in 120 days and was most intense under air+water circulation treatment. Gas emissions and C-budget calculations did not show any reliable correlation with bacterial decay intensity. Sediment nitrate addition prevented bacterial decay in wood samples but sediment pH was also affected by such additions. We conclude, therefore, that wood surrounded by low sediment nitrogen concentrations is more likely to be affected by bacterial attack than is wood in nitrogen-rich sediments. Glucose and SO2−4 addition also prevented bacterial attack on other lignocellulosic test materials (kapok fibres) after 28 days, indicating that reducing the redox potential might serve as a protection strategy.