RATES OF LEACHING OF CS-137 AND POTASSIUM FROM DIFFERENT PLANT LITTERS

Mature plants of Calluna vulgaris, Trifolium repens and Agrostis capillaris were dug up from field sites. Plants were artificially labelled with Cs-137 by uptake through the roots from a liquid medium. Shoot material was allowed to dry to give plant litters adequately labelled for leaching experiments, using microcosms subjected to a number of applied treatments. Measurements were made of Cs-137 activity, potassium content and pH on the leachates from each microcosm obtained every 2 weeks over a 3-month period. The respiration rate of the litter was also measured to give an index of microbial activity. At the end of the experiment, Cs-137 and K contents of the residual litter were measured. Generally, the rate of release of Cs-137 from Calluna litter was slower than that from Trifolium or Agrostis. After 3 months, the loss of Cs-137 from Calluna litter had stabilised at about 30-40% of the original (i.e. 60-70% remained in the litter). Trifolium had lost 60% of the initial Cs-137 over the same period, whilst Agrostis had lost about 70%. Repeated drying and rewetting treatment, compared to a continuous moistened state, resulted in the stabilisation of Cs-137 within Trifolium and Agrostis litters. In Agrostis and Trifolium, the release of potassium was greater and more rapid than the release of Cs-137, with only 10% of the original K remaining in the litter after 2 months. In Calluna, the release of K resembled the release of Cs-137 more closely.