Diatom assemblages of non-living substrates in petrifying Cratoneurion springs from lower Belgium

Abstract

Diatom assemblages were examined from non-living substrates in thirteen springs supporting the Natura 2000 habitat type 'Petryfing springs with tufa formation' in the southern part of Flanders. More than 300 taxa were recorded, including some which appear to be particularly associated with this kind of environment. Even though a number of characteristic taxa and diatoms characterizing fast-flowing springs of more elevated terrain remained absent, local species richness was higher than reported from carbonate springs elsewhere in Europe. Relative abundance of 'Red List' taxa was, however, substantially lower. Taxon richness was not related to measured nutrients but increased with diatom-inferred trophic status. Assemblages consisted mainly of motile, small-celled species of Achnanthidium, Amphora, Caloneis, Planothidium and Stauroneis. Hygropetric rheocrenes presented a somewhat more distinct assemblage than helocrene and rheohelocrene settings, but overall, compositional metrics were similar among spring types. Assemblages were structured mainly along gradients of pH, major ions (in particular magnesium and potassium) and nitrate relating to calcite precipitation, aquifer and nitrogen supply. Besides substantiating broad similarities among Cratoneurion springs, the results provide arguments for a regionalized approach towards assessment of their diversity, community structure and conservation status.