Comparison of the utility of a frequently used diatom index (IPS) and the diatom ecological guilds in the ecological status assessment of large rivers
Trábert, Zsuzsa; Tihamér Kiss, Keve; Várbíró, Gábor; Dobosy, Péter; Grigorszky, István; Ács, Éva
published: Jan 1, 2017
Open Access (paper can be downloaded for free)
The Indice de Polluo-Sensibilité Spécifique (IPS) is one of the most frequently used diatom indexes. However, according to some studies on streams and small rivers, the diatom ecological guilds might be more effective tools for ecological quality assessment in the future, but their usability is not always clear. Our main goal was to compare the robustness of the IPS index and diatom ecological guilds in a large river. For this: i) a temporary study was carried out to investigate if there were some differences between how the nutrient content affected the IPS values and guild proportions in the Danube River; ii) spatial studies were conducted to investigate the effects of the different water depths (different light intensity and current velocity) on biological metrics (such as IPS and guilds); iii) we studied whether the IPS index or guild proportions were influenced more by the substrate type. As for the results of the temporal study, only the motile and planktic guilds had significant connections with phosphate- phosphorus concentration. However, the high profile and the low profile taxa showed correlations neither with nutrient concentration nor water discharge. Nevertheless, the higher the abundances of the low profile guild, the lesser the values of the IPS index. In spatial studies, the guild abundances (especially the motile taxa) altered at different water depths. This could be caused by different microhabitats characterised by a disparate current velocity, and by different types of bed material along the cross-section. Contrary to guilds, there were no relevant differences in IPS values along the cross-sections. We experienced similarities in the study on shells and in the spatial study: there were significant differences between guild abundances on different shell surfaces, but not so in the IPS. On the whole, the IPS is robust enough to be a suitable index for ecological water quality assessment, and diatom ecological guilds cannot be used instead of the diatom index (IPS) in large rivers. However, the trait-based methods could be useful supplements to the ecological status assessment.