Ilus Erkki, Saxén Ritva
STUK-Radiation and Nuclear Safety Authority, PO Box 14, FIN-00881 Helsinki, Finland.
J Environ Radioact. 2005;82(2):199-221. doi: 10.1016/j.jenvrad.2005.01.008. Epub 2005 Mar 17.
The amount and vertical distribution of Chernobyl-derived 137Cs in the bottom sediments of some Finnish lakes were studied. Sediment and surface water samples were taken in 2000 and 2003 from 12 stations in nine lakes and the results were compared with those obtained in corresponding surveys carried out in 1969, 1978, 1988 and 1990. Each of the five deposition categories of Chernobyl fallout in Finland were represented. The depth profiles of 137Cs in the sediments showed considerable variety in the lakes studied. The peak values varied between 1.5 and 46 kBq kg(-1) dry wt. The size and shape of the peak did not always correlate with the amount of deposition in the area, but on the other hand, reflected differences in sedimentation processes in different lakes. In some of the lakes the peak still occurred in the uppermost (0-2 cm) sediment layer, but in an extreme case the peak occurred at a depth of 22-23 cm corresponding to a sedimentation rate of 16 mm year(-1) during the 14 years after the Chernobyl accident. The total amounts of 137Cs in sediments varied from 15 to 170 kBq m(-2) at the sampling stations studied. Since 1990, the amounts have continued to increase slightly in two lakes, but started to decrease in the other lakes. In most of the lakes, the total amounts of 137Cs in sediments were about 1.5-2 times higher than in local deposition. In two lakes, the ratio was below 1, but in one case 3.2. Compared with the total amounts of 137Cs at the same stations in the late 1960s and 1970s, the values were now at their highest, at about 60-fold. The most important factors affecting 137Cs values in sediments were the local amount of deposition and the type of the lake and the sediment, but in addition, there were a number of other factors to be considered.
对芬兰一些湖泊底部沉积物中源自切尔诺贝利的137铯的含量及垂直分布进行了研究。2000年和2003年从9个湖泊的12个站点采集了沉积物和地表水样本，并将结果与1969年、1978年、1988年和1990年进行的相应调查结果进行了比较。芬兰切尔诺贝利沉降物的五个沉积类别均有代表。所研究湖泊中沉积物中137铯的深度剖面显示出相当大的差异。峰值在1.5至46 kBq kg(-1)干重之间变化。峰值的大小和形状并不总是与该地区的沉积量相关，但另一方面，反映了不同湖泊沉积过程的差异。在一些湖泊中，峰值仍出现在最上层（0 - 2厘米）沉积物层，但在一个极端情况下，峰值出现在22 - 23厘米深处，这对应于切尔诺贝利事故后14年期间16毫米/年的沉积速率。在所研究的采样站点，沉积物中137铯的总量在15至170 kBq m(-2)之间变化。自1990年以来，两个湖泊中的含量继续略有增加，但其他湖泊开始下降。在大多数湖泊中，沉积物中137铯的总量比当地沉积量高约1.5 - 2倍。在两个湖泊中，该比例低于1，但在一个案例中为3.2。与20世纪60年代末和70年代同一站点的137铯总量相比，现在的值处于最高水平，约为60倍。影响沉积物中137铯值的最重要因素是当地沉积量、湖泊和沉积物的类型，但此外，还有许多其他因素需要考虑。
