Phosphatic Microbial Biofilms Cementing Gravels in a Vadose Environment

Abstract

Excavations through a barrier beach at Montrose on the north-east coast of Scotland revealed a coarse gravel beneath the surface. Within the tidally driven zone of the water table this is sufficiently cemented to impede penetration and to bend sheet steel piling emplaced to support the excavations. The remarkable feature of this cement is that it is a microbial biofilm and contains no mineral material. This is the first record of biofilms forming in coarse sediments and imparting such high strength characteristics, and also of their formation in what is essentially a vadose environment.

A high phosphorous content may have implications for the development of phosphate cements elsewhere.