Adaptation of phytoplankton-degrading microbial communities to thermal reactor effluent in a new cooling reservoir

Abstract

The reactor is a nuclear materials production facility at the Savannah River Plant, 13 km north of the Savannah River, South Carolina. For experiments that were begun during reactor shutdown, aerobic decomposition occurred at temperatures of <55°C. After 2 months of reactor operation, aerobic rates increased substantially at 55 and 70°C, although maximum rates were observed at temperatures of ≤40°C. The temperature range for which maximum anaerobic mineralization (ie the sum of CH4 and CO2) was observed was 25-40°C when the reactor was off, expanding to 25-55°C during reactor operation. Increased rates at 55°C, but not 70°C, correlated with an increase in the ratio of cumulative CH4 to CO2 produced over 21 days. When reduced reactor power lowered the maximum temperature of the reservoir to 42°C, aerobic decomposition at 70°C was negligible, but remained substantial at 55°C. Selection for thermophilic decomposers occurred rapidly in this system in both aerobic and anaerobic communities and did not require prolonged exposure to elevated temperatures. -from Authors