[M-IS14] Biogeochemistry

[MIS14-P04] Spatial pattern of radiocesium concentration in acidic river systems

*Yasunori Igarashi¹, Keitaro Fukushima¹, Asuka Saito¹ (1.Fukushima University)

Keywords:Radiocesium, River

Radiocesium from the nuclear disaster still persists in rivers. While the distribution of cesium between solid and liquid phases is known to be influenced by clay minerals and cation concentrations, its behavior in rivers upstream of volcanic areas with low pH remains uncertain. This study investigated the spatial distribution and factors influencing ¹³⁷Cs concentration in river water, including pH, major cation and anion concentrations (e.g., ammonium, nitrate, phosphate), suspended solids, and dissolved and particulate ¹³⁷Cs concentrations, in October 2023. Findings revealed that pH levels in the middle reaches of the Arakawa River were notably reduced by acidic tributaries from volcanic sources, leading to heavy metal precipitation in the riverbed as these tributaries were neutralized. This process likely affects the distribution of radiocesium between solid and liquid phases. The study offers insights into the spatial variability of dissolved ¹³⁷Cs and particulate ¹³⁷Cs in this water system, with discussions on determinants of river water quality variability.