The distribution of 137Cs in sediments of the littoral zone of a former reactor cooling pond

Previous studies in Pond B, a 12-m deep, 82-ha reservoir that once served as a reactor cooling pond, had (i) suggested the preferential accumulation of 137Cs in sediments at a water depth of 3m within the littoral zone and (ii) attributed this accumulation to the effects of either macrophyte vegetation or sediment slope. To test for the preferential accumulation of 137Cs at intermediate depths within the littoral zone, sediment cores were taken at water depths of 0.5, 1, 2, 3, 4 and 5 m along 6 transects in Pond B. The sediment structure was similar at all water depths in the littoral zone with a surface layer of 0.02–0.04 m of plant debris and fine sediments over a base of sandy sediments. The 137Cs was largely restricted to the surface layer of fine sediments, and there was no indication of preferential accumulation of fine sediments or 137Cs at water depths of 3 m. There was no apparent relationship between sediment slope and 137Cs content. Although the 137Cs entered Pond B more than 20 years ago, its prevalence in the surface layers of littoral zone sediments resembles the pattern observed for 134Cs deposited in European lakes from the recent Chernobyl accident.