2:20 PM - 2:35 PM
[MAG34-03] The Changes of 137Cs Runoff due to Littter Removal in Forest Headwater Catchmrnt
Keywords:Cs-137, Forest Headwater Catchment, DOC, Decontamination
In the forests affected by the Fukushima Daiichi NPP accident, decontamination has only been carried out within a 20 m radius from residental areas, and most of these areas remain undecontaminated. The forests discharge 137Cs through rivers, and it has been observed that the concentrations of dissolved 137Cs increace when water flows out of the forests. This is thought to be due to soil infilration water runoff and leaching from sedimentary litter as a result of rising groundwater levels. Desorption from the suspended sediments by ion exchange with K+ is also considered to be the origin of dissolved 137Cs. In this study, the effect of sedimentary litter on the discharge of 137Cs from a forest headwater catchment in the Yamakiya area, Kawamata town, Fukushima prefecture, was investigated by removing litter near the river channel, and K+ and Dissolved Organic Carbon (DOC) concentrations were measured as indicators of ion exchange and organicmatter leaching, respectively.
Sampling was carried out every month, with additional intensive observations during rainfall runoff events. Sampling during runoff events was carried out before decontamination during an event with a total rainfall of 51.5mm from 14 to 15 July 2024 and after deconaminaion during an event with a total rainfall of 28mm from 2 to 3 November 2024. A comparision of 137Cs runoff per flow rate before and after decontamination showed a 2.5-fold increase in dissolved 137Cs from 0.0069 Bq/L to 0.0178 Bq/L, and no significant change change in suspended 137Cs from 45.891 Bq/L to 40.112 Bq/L. Before decontamination, dissolved 137Cs and DOC increased 10-fold and K+ concentrations increased 5-fold at outflow compared to the average concentrations in baseflow, and 137Cs and DOC concentrations remaind higher than in normal water after the flow peak. After decontaminaton, the rate of the rate of increase in dissolved 137Cs, DOC and K+ concentrations decreased by a factor of 3,4 and 2.5 times, respectively. The amount of dissolved and suspended 137Cs discharged decreasing and the amount of suspended 137Cs discharged increasing, with the proportion of the suspended form increasing from 99.15 % to 99.84 % . Dissolved 137Cs and DOC concentrations remaind high after the peak discharge while K+ concentrations decreased to the mean of baseflow, suggesting that the increase in dissolved 137Cs concentrations during discharge was due more to leaching from organic matter than ion exchange.
These results suggest that the removal of litter near the river channel may reduce the extent of the increace in dissolved 137Cs concentration at runoff, and that the removal of litter cover stimulates sedimend productuion in the catchment and increaces the discharge of suspended 137Cs. On the other hand, during the baseflow period, the concentration of dissolved 137Cs increased and the DOC concentration also increased, even though there was no change in the amount of suspended 137Cs discharge, suggesting that thw increase in soil temperture due to litter removal accelated the decomposition of sedimentary organic matter and the dissolved 137Cs was leached out.
Sampling was carried out every month, with additional intensive observations during rainfall runoff events. Sampling during runoff events was carried out before decontamination during an event with a total rainfall of 51.5mm from 14 to 15 July 2024 and after deconaminaion during an event with a total rainfall of 28mm from 2 to 3 November 2024. A comparision of 137Cs runoff per flow rate before and after decontamination showed a 2.5-fold increase in dissolved 137Cs from 0.0069 Bq/L to 0.0178 Bq/L, and no significant change change in suspended 137Cs from 45.891 Bq/L to 40.112 Bq/L. Before decontamination, dissolved 137Cs and DOC increased 10-fold and K+ concentrations increased 5-fold at outflow compared to the average concentrations in baseflow, and 137Cs and DOC concentrations remaind higher than in normal water after the flow peak. After decontaminaton, the rate of the rate of increase in dissolved 137Cs, DOC and K+ concentrations decreased by a factor of 3,4 and 2.5 times, respectively. The amount of dissolved and suspended 137Cs discharged decreasing and the amount of suspended 137Cs discharged increasing, with the proportion of the suspended form increasing from 99.15 % to 99.84 % . Dissolved 137Cs and DOC concentrations remaind high after the peak discharge while K+ concentrations decreased to the mean of baseflow, suggesting that the increase in dissolved 137Cs concentrations during discharge was due more to leaching from organic matter than ion exchange.
These results suggest that the removal of litter near the river channel may reduce the extent of the increace in dissolved 137Cs concentration at runoff, and that the removal of litter cover stimulates sedimend productuion in the catchment and increaces the discharge of suspended 137Cs. On the other hand, during the baseflow period, the concentration of dissolved 137Cs increased and the DOC concentration also increased, even though there was no change in the amount of suspended 137Cs discharge, suggesting that thw increase in soil temperture due to litter removal accelated the decomposition of sedimentary organic matter and the dissolved 137Cs was leached out.