Observations of sedimentation of diatoms in some Finnish rivers

Abstract

reservoirs of the rivers Kemijoki (Valajaskoski, Isohaara), Oulujoki (Pyhäkoski), Kokemäenjoki (Kolsi, Tyrvää), Paimion­joki (Juva), Pielisjoki (Kuurna) and in the channel of Lake Höytiäinen (Pun­tarikoski). The proportion of marine, brackish and clear‑water forms should be seen as secondary diatoms. These originate from sediments accumulated during the different stages of the Baltic Sea. As a result of river erosion, the marine and brackish water forms (Yoldia Sea stage and Litorina Sea stage) range from 1 to 15 % and the clear‑water forms (Ancylus Lake stage) from 1 to 17 % of the counted diatoms. This should be taken into consideration when interpreting diatom deposition in the estuary areas. The character of the drainage area – its geology and also the limnology of its lakes – is clearly reflected in the pH ecological groups of the diatom flora examined. This result agrees with the quality of the river water and that of the sediments at the sampling sites.