The dynamics of radiocesium in the hydrosphere ecosystem of exclusive inland lakes (Lake Onuma)

Abstract

  After the accident at FDNPP, the effects of radioactive Cs were observed on wakasagi in Lake Onuma,Gunma Prefecture. Lake Onuma is an exclusive inland lake of the hydrosphere ecosystem. The decay rate of 137Cs concentration in lake water has been almost constant since 2015. We examined the seasonal dynamics of the activities Cs in wakasagi and lake water. In Lake Onuma, from June to October, the upper and deep layers of the lake form a thermocline and do not circulate. At that time, the amount of dissolved 137Cs increases in the deep layer and the state becomes anoxic. We are investigating the adsorption rate of radioactive Cs in the sediment of Lake Onuma. In addition, stable Cs in the sediment is also analyzed to investigate the relationship with the adsorption of radioactive Cs.