Biofilms in the Critical Zone: Distribution and mediation of processes

Microbial biofilms occur in all levels of the Critical Zone (CZ); they are on and in the vegetation, throughout the soil-saprolite zone, and along fractures in deep subsurface. Here we discuss biofilms in each level of the CZ with a focus in the soil-saprolite continuum. We show how scanning electron microscope (SEM) images provide an appropriate scale to explore microbe mineral interactions in the CZ and can be used without extensive sample preparation. Through SEM imaging, we show that biofilms weather primary minerals, that macropores and fractures are hotspots of biofilm development, that biologic precipitation of short-range-order minerals (SROs) occurs in biofilms, and that biofilms are important in the process of organic matter stabilization.