Diatom communities of lake/stream networks in the Tatra Mountains, Poland, and the Swiss Alps

Diatom communities in alpine-zone streams of the Tatra National Park and the Swiss National Park were heterogeneous with respect to species richness, abundance, Shannon diversity index, and ecological preference. Two groups of diatoms were distinguished. Group 1, inhabited streams in the upper Gasienicowa Valley (Tatra Mts) and Macun Lakes region (Alps), and had high species richness and Shannon diversities (especially in the Tatra Mts streams) but low abundances. The most abundant and common diatoms were Psammothidium helveticum, Diatoma mesodon, Aulacoseira alpigena, Achnanthidium minutissimum, Psammothidium subatomoides, Psammothidium marginulatum, and Gomphonema parvulum. Group 2 inhabited Tatra Mts streams in the Five Polish Lakes Valley and lower Gasienicowa Valley. Diatoms were highly abundant but species richness and Shannon diversities were relatively low. The most abundant were Achnanthidium minutissimum, Diatoma mesodon, Fragilaria capucina gracilis group and Tabellaria flocculosa. There was no clear difference between the diatom communities of the outlet streams of upper lakes and the inlet streams of adjacent downstream lakes. The high abundance of diatoms in the streams of the Tatra Mts suggests recent ecosystem changes related to lake eutrophication and partly by weather anomalies resulting from climate change.