Growth and calcification of Vaucheria (Xanthophyta) on a travertine surface in a temperate freshwater setting

Six species of Vaucheria were identified in calcified mats growing on a shaded travertine surface. Growth was seasonal and strongly influenced by irradiance but little influenced by temperature which was consistently below 15 degrees C. Calcification of Vaucheria was low at the mat surface but increased rapidly with depth and was significantly higher on empty siphons. Crystals of calcite were randomly distributed on the siphons, and consisted almost entirely of combinations of the flat rhombohedron and prism. Vaucheria oospores were occasionally calcified preferentially suggesting some biological control of the process. Calcification was influenced to some extent by photosynthesis, but was mainly the result of carbon dioxide evasion from a turbulent, bicarbonate-rich stream water.