Biogeochemical cycling of iron: Implications for biocementation and slope stabilisation.

Abstract Microbial biofilms growing in iron-rich seeps surrounding Lake Violao, Carajas, Brazil serve as a superb natural system to study the role of iron cycling in producing secondary iron cements. These seeps flow across iron duricrusts (referred to as canga in Brazil) into hydraulically restricted lakes in northern Brazil. Canga caps all of the iron ore deposits in Brazil, protecting them from being destroyed by erosion in this active weathering environment. Biofilm samples collected from these seeps demonstrated heightened biogeochemical iron cycling, contributing to the relatively rapid, seasonal formation of iron-rich cements. The seeps support iron-oxidising lineages including Sideroxydans, Gallionella, and an Azoarcus species revealed by 16S rRNA gene sequencing. In contrast, a low relative abundance of putative iron reducers; for example, Geobacter species (