Characterising physicochemical sediment conditions at selected bacterial decayed wooden pile foundation sites in the Netherlands, Germany, and Italy

We investigated the relationship between wood degradation caused by erosion bacteria and the physicochemical properties of foundations with wooden piles from sites in the Netherlands, Germany, and Italy. Wooden foundation piles have been widely used to stabilise urban settlements along coastal areas and river sites for several millennia. Recently a number of these buildings have suffered from structural instability because their foundations have suddenly lost supporting strength. This loss of strength has been associated with the activity of erosion bacteria that can colonise and destroy wood under low-oxygen conditions, such as those that exist below the groundwater level. Knowledge of bacterial species involved in this process and their growth requirements is sparse, but it has been documented that the damage to wooden foundation piles caused by these bacteria can occur relatively rapidly. Redox potential (platinum electrodes) measurements, sediment, and sedimental water samples were obtained from nine European sites. Sediments were characterised and analysed for total contents of carbon, nitrogen, sulphur, phosphate, and major cations, whereas sedimental water was analysed for pH, conductivity, total and dissolved carbon and nitrogen, NH 4 + , NO 3 - , SO 4 2 - , PO 4 3 - , Cl - , and major cations. The chemical sediment composition was governed mainly by sediment type (sand, clay), whereas sediment water composition reflected the exposure to sea or freshwater and the redox status of the sampling location. Bacterial wood decay was detected at all sites but with different magnitude orders reflecting the different environments. When the physicochemical properties of sedimental water from foundations in sandy sediments were compared with wood degradation levels, it was observed that decreasing total nitrogen concentration, but not that of phosphate, accompanied increasing bacterial wood decay.