HETEROGENEITY OF DEEP SUBSURFACE MICROORGANISMS AND CORRELATIONS TO HYDROGEOLOGICAL AND GEOCHEMICAL PARAMETERS

Nineteen samples were obtained from a 21-m(3) section of zeolitized vo lcanic ash-fall tuff 390 m below the surface of Rainier Mesa, Nevada. Rock mined aseptically from the walls of deep subsurface tunnels provi ded pristine samples for microbiological and geochemical analyses. Mic robiological parameters measured on all samples included direct counts and the abundance, diversity, morphology, and metabolic traits of cul turable organisms. Physical and chemical parameters measured included ionic and nutrient chemistries, mineralogy, porosity, moisture content , and permeability. The results indicate that the culturable microbiol ogical community size and composition exhibit random spatial variabili ty within the geologically/geochemically homogeneous rock section. The relative abundance of microorganisms testing positive for nitrate red uctase demonstrated a spatial trend along the vertical and front-to-ba ck axes of the rock section by gradient analysis. The porewater concen tration of nitrate correlated with numbers of bacteria testing positiv e for nitrate reductase and indicates that these bacteria may exist as dormant forms in situ.