Temporal variability of Achnanthidium minutissimum (Kützing) Czarnecki and its relationships to chemical and hydrological features of the Torna-stream, Hungary
Establishment of indicator values of species used in any kind of environmental quality assessment system has been of essential importance. This need is increased in case of species that are abundant. Achanthidium minutissimum has been, inevitably, one of the most frequently occurring diatom species all over Europe. Some authors list is as r-strategist aquatic weed that idndicates disturbed environment. The aim of our study was to analyze the temporal distribution of A. minutissimum in relation to physical and chemical parameters and to evaluate the data on basis of the existing diatom indices. In 2004-2005, diatom samples were taken biweekly and water samples for chemical analyses were collected once a month in the Torna-stream, W-Hungary. The diatom assemblages showed marked seasonal distribution, and the relative abundance of the A. minutissimum also varied throughout the year. We could find no clear correlation between the relative abundance of the a. minutissimum and either the fluctuation of the nitrogen and phosphorus forms or the major ions. Instead, there was significant correlation with Si content of the water which correlated with the seasonal changes of the discharge. The relative abundance of the A. minutissimum ashowed significant positive correlation with three diatom indices (IBD, EP-D, TDI): the higher abundance of the species resulted in better water quality. Against the IPS index (which is recommended to apply for ecological status assessment of Hungarian streams) we did not find significant correlation, consequently this index does not use the A. minutissimum as a potential indicator species.
Based on the data we conclude that the discharge-dependent Si content of the streamwater and the r-strategy of the species determine the distribution of the A. minutissimum; it typically reaches higher dominance after flood periods and therefore indicates natural disturbances. Since flooding is a natural phenomenon existing also in reference state, the species’ abundance can not be used to assess the antropoghenic impacts. According to most diatom sampling protocols for WFD qualification, periods after floods should be avoided. In this view we may conclude that high contribution of A. minutissimum in any sample may indicate a preceding flood and therefore such samples do not provide a reliable basis for ecological status assessment
