Establishment of equilibrium states and effect of disturbances on benthic diatom assemblages of the Torna-stream, Hungary

摘要

This paper analyses the establishment of equilibrium states in relation to natural disturbances in epilithic diatom assemblages. Sterilized limestone bricks were exposed between April 2008 and 2009 in the Torna-stream and were removed one by one on every third day in the first month and then weekly until May 2010. Physical and chemical parameters were measured on the field and in laboratory. Equilibrium states were restricted to three separate months: July 2008, May and January 2009 taking the consistence of biomass (chlorophyll-a) into consideration. Cocconeis placentula sensu lato, Fragilaria vaucheriae, Gomphonema parvulum, G. olivaceum, Navicula gregaria, N. lanceolata, Nitzschia linearis, and Surirella brebissonii took part in the equilibrium assemblages, two of which dominated by a single species. Analyses of environmental constancy during equilibrium phases allowed concluding that resilience of a developed equilibrium phase may ensure biotic constancy even though the underpinning environmental background fluctuates at higher amplitude. The conclusions of our study on attached stream diatom assemblages are similar to those found for temperate lakes: equilibrium states are rare, unpredictable, ephemeral, may occur both in relatively stable and strongly fluctuating environments, and are mostly characterized by monodominance, but contrary to phytoplankton, their establishment requires a longer time to develop corresponding to differences in generation times.