Microbial colonization and weathering of silicates in a petroleum-contaminated groundwater

The influence of native microorganisms on mineral dissolution and precipitation was examined in a petroleum-contaminated aquifer near Bemidji, Minnesota. In-situ microcosms containing clean silicate fragments were established in the contaminated, microbially active groundwater over one-year periods. The recovered minerals were then examined by SEM and ESEM for microbial colonization patterns and weathering features. These experiments reveal distinct patterns of colonization and weathering associated with microbial attachment and growth. Microcline, anorthoclase, and oligoclase were widely colonized, and the colonized surfaces deeply weathered, with secondary clays precipitated on some uncolonized surfaces. Other feldspars, in contrast, were uncolonized and unweathered. Specific mineral removal rate was estimated from etch pit depth, while bulk weathering rate was estimated from the rate of change of silica concentration in the groundwater. In this system the primary control of silicate dissolution is apparently microbial colonization and metabolic activity.