Development of methods for collecting the stemflow on the trunk of trees contaminated with radioactive fallout

Abstract

Methods have been developed and evaluated to collect137Cs in stemflow to investigate the possibility of secondary radiocaesium contamination via stemflow in Japanese persimmon (Diospyros kaki Thumb.) orchards. Collection pads were made by encapsulating sphagnum or absorbent cotton in a tea pack (polyester-polyethylene composite fiber). In addition, stemflow was collected directly by a plastic zipper bag (collection bag). A significant linear relationship between the amount of137Cs per 1 g sphagnum collected and the accumulated precipitation over the measurement period was evident, indicating a close relationship between outflow of137Cs from the bark and precipitation. There was a significant difference between the percentages of dissolved137Cs to the total137Cs in stemflow collected by the sphagnum pads and the collection bag (Kruskal-Wallis test, P<0.01), suggesting that organic mediums consisting mainly of cellulose should not be used for the investigation of dissolved137Cs. The weight of stemflow, the amount of137Cs in particulate form and the total137Cs in the stemflow collected with sphagnum were significantly higher than those in the water collected with cotton. Accordingly, it is concluded that collection pads using sphagnum are more appropriate as stemflow collectors to quantify secondary deposition because of enabling to fix anywhere.