MICROBIAL COLONIZATION AND WEATHERING OF SILICATES IN A PETROLEUM-CONTAMINATED GROUNDWATER

The influence of native microorganisms on mineral dissolution and prec ipitation was examined in a petroleum-contaminated aquifer near Bemidj i, Minnesota. In-situ microcosms containing clean silicate fragments w ere established in the contaminated, microbially active groundwater ov er 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 weather ing associated with microbial attachment and growth. Microcline, anort hoclase, and oligoclase were widely colonized, and the colonized surfa ces deeply weathered, with secondary clays precipitated on some uncolo nized surfaces. Other feldspars, in contrast, were uncolonized and unw eathered. Specific mineral removal rate was estimated from etch pit de pth, 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.