2024 年 58 巻 1 号 p. 11-22
To elucidate the role of Himalayan river systems in the global carbon cycle, I have conducted sampling surveys and studied carbonate systems in these rivers. On modern timescales of 1–100 years, I showed that abundant soil-derived CO2 was released from the surface water to the atmosphere. On the geological timescales of more than 10,000 years, I re-evaluated chemical weathering of both silicate and carbonate rocks and the atmospheric CO2 consumed in the basins. I also investigated the dynamics of radiocesium (137Cs) released by the Fukushima Dai-ichi Nuclear Power Plant accident in 2011 and its decadal trends, in Fukushima forest soils. I showed that most of the radiocesium is now retained on the surface of the mineral soil horizon, and that the distributions of radiocesium in each forest compartment (e.g., tree leaves/needles and forest soils) are entering the “quasi-equilibrium steady-state”. In addition, I highlighted the potential importance of organic matter in forest soils as a temporary reservoir of radiocesium and as a source for radiocesium cycling in forest ecosystems.