Effects of deposited litter on water quality and radiocesium runoff in a forested headwater basin

永田 祐太郎*; 恩田 裕一*; 平松 翼*; 高橋 純子*; 榊原 厚一*; 新里 忠史  

Nagata, Yutaro*; Onda, Yuichi*; Hiramatsu, Tsubasa*; Takahashi, Junko*; Sakakibara, Koichi*; Niizato, Tadafumi

This study aims to investigate the effect of litter on the discharge of dissolved Cs in a forested headwater catchment. We sampled stream water, groundwater, and water passing through litter to measure dissolved Cs, ions, and DOC. Additionally, we examined changes in river water quality and dissolved Cs concentrations by removing litter near the river channel, simulating forest decontamination. Sampling was conducted monthly and during rainfall events with totals of 26 mm and 51.5 mm. Results indicated that at runoff peaks, dissolved Cs concentrations were over ten times higher than baseflow levels, with concurrent increases in DOC and K concentrations. While Cs and DOC concentrations remained elevated the day after rainfall, K concentrations returned to baseflow levels within four hours after the runoff peak. This suggests that leaching from organic matter significantly contributes to the increase in dissolved Cs concentration during runoff, much more than ion exchange with K. The study also reports changes in water quality and Cs concentrations following litter removal experiment in the watershed.