Seasonal changes of magnetic susceptibility in sediments from Lake Zywiec (South Poland)

Lake Zywiec is a man-made lake constructed in 1965 on the Sola River, Beskidy Mountains (South Poland). The lake is the largest one in a flood control reservoir system known as the Sola Cascade. In May and September 1970, separated by a big flood event in July, the lake was sampled for rock magnetic, chemical and granulometric studies. In 85% of the September samples, susceptibility decreases by 10 to 40% compared to the value measured in May. Seasonal changes are also observed in the total Fe content and some heavy metals. A general decrease in Zn, Pb, Cd, Cu and Cr content during the summer season was observed in the whole lake. The content of other metals such as Mn and Ni increased in samples taken in September. The changes observed in the lake sediments could be only an accidental result of the flood or may indeed result from seasonal changes fostered by the flood effect.