Metabolic rates of subsurface microorganisms in a hydrogeochemically characterized granitic aquifer system at the Mizunami Underground Research Laboratory (MIU) in Japan

Fukuda, Akari; Kozuka, Mariko*; Konno, Yuta*; Aosai, Daisuke; Hagiwara, Hiroki; Mizuno, Takashi; Suzuki, Yohei*

no journal, , 

To quantify microbial influences on the hydrogeochemistry of a 99-1169-m deep granitic aquifer system, we developed methodology for sensitive measurements of a variety of aerobic and anaerobic metabolic activities. Briefly, microbial cells were ca. 30-fold concentrated in groundwater by filtration to incubate with electron acceptors. Aerobic respiration was more than 400 umol/L/year at depths of 99 and 175 m and decreased with increasing depth down to 36 umol/L/year at a depth of 1169 m. Nitrate respiration increased from 99 to 308 m (4.3 to 37 umol/L/year) and decreased with increasing depth down to 0.20 umol/L/year. Sulfate respiration ranging from 1.4 to 3.2 umol/L/year was detected only at depths above 200 m. The depletion of O and NO and a gradual decrease in sulfate with increasing depth in the granitic aquifer could be attributed to microbial respirations at rates clarified in this study. Our research was partially founded by Nuclear and Industry Safety Agency.