Diatom communities of springs in the Southern Alps

In the Adamello-Brenta Regional Park (Trentino, Italy), the diatom communities of 30 mountain springs, 15 on crystalline and 15 on carbonate substratum, were studied between 1993 and 1996. Two of them, one from each substratum type, were sampled monthly for a more detailed investigation of seasonal changes in community structure. The diatom flora of these springs consisted of 250 diatom taxa and showed similarities with springs and headwater stream diatom communities from different geographic areas. Characteristic spring taxa (crenophiles) were present, but included mainly subdominant and rare taxa. Diatom taxa numbers were similar to those found for mountain streams with the lowest values found for stones in carbonate springs; nevertheless the community structure of epilithic and epiphytic samples was found to be similar and more or less constant over the seasons. By numerical methods, diatom communities were clearly related to a pH gradient. A group of species, located at the lower end of this gradient, is typical of anthropogenetically acidified running waters.