Improvement of the ecological water qualification system of rivers based on the first results of the Hungarian phytobenthos surveillance monitoring

Results of an ecological quality ratio-based qualification system, developed on the basis of the analysis of 1,161 benthic diatom dataset of the Hungarian national database, are presented herein. Using Kohonen’s Self Organising Map technique, the 25 Hungarian physiographic river types were pooled into six larger distinct categories (diatom river groups). Diatom metrics were tested for their sensitivity to the targeted stressors (nutrients, COD hydromorphological alteration) in each group. The strongest relationships were found in the case of the IPS, SI and TI indices; therefore the average of these metrics (IPSITI) was proposed as a national multimetric index for Hungarian streams. Based on IPSITI values, the ratio of moderate to worse quality water was the highest in those groups containing small rivers. In the case of large, lowland and mid-altitude rivers with fine sediment, the good and moderate ecological status was more characteristic. Applicability of the IPSITI seems to be very useful in case of small- and medium-sized rivers. For these rivers, the index showed a significant relationship with nutrients and organic pollutants. In the case of very large rivers, the stressor–index relationships were not significant because of the insufficient number of samples and the small range of stressors.