Comparison of the utility of a frequently used diatom index (IPS) and the diatom ecological guilds in the ecological status assessment of large rivers

Abstract

The Indice de Polluo-Sensibilité Spécifique (IPS) is one of the most frequently used diatom index. Beside this, according to some studies in streams and small rivers the diatom ecological guilds might be effective tools for ecological quality assessment in the future, but the usability of them 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 guilds 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 (IPS and guilds, as well); 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 abundances the low profile guild reached the lesser values of the IPS index were. In spatial studies the guild abundances (especially the motile taxa) altered in different water depths. This could be caused by 2 different microhabitats characterised by 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 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 the ecological water quality assessment and diatom ecological guilds could not be used instead of the diatom index (IPS) in large rivers. However, the trait based methods could be useful supplements of the ecological status assessment.

Expanding the trait-based concept of benthic diatoms: Development of trait- and species-based indices for conductivity as the master variable of ecological status in continental saline lakes

“…However, other, well-known functional traits (planktic life form, high and low profile ecological guilds) may indicate lower conductivity values, similarly to S4 size. Trábert et al (2017) showed already that the relative abundance of diatom taxa under the high profile and motile guilds correlated with each other negatively in lotic systems. The abundance of diatoms belonging to the high profile guild is not directly related to the nutrient level, rather to other habitat factors (Soininen et al 2016) like high light intensity (Trábert et al, 2017).…”

“…Trábert et al (2017) showed already that the relative abundance of diatom taxa under the high profile and motile guilds correlated with each other negatively in lotic systems. The abundance of diatoms belonging to the high profile guild is not directly related to the nutrient level, rather to other habitat factors (Soininen et al 2016) like high light intensity (Trábert et al, 2017). The dominance of low profile diatom taxa is characteristic in temporary and permanent water courses with frequent disturbance events and low nutrient content (Novais et al, 2014).…”

Long-Term Changes of Species Composition and Functional Traits of Epiphytic Diatoms in the Szigetköz Region (Hungary) of the Danube River

“…Beside abiotic factors, biotic factors (e.g., interspecific competition) also affect the relative abundance of these traits. Regarding traits related to the attachment mechanism and lifeform of diatoms, the proportion of high-profile groups in running waters is typically low because they have a long stalk that attach to the substrate and is easily torn off by flowing water [51,52]. During periods of low water discharge, their proportion was slightly higher in the epiphyton, partly because they are adapted to low current velocities [53].…”

“…Therefore, the amount of this group is typically the largest in flowing aquatic habitats. This group is also the dominant ecological group in the epiphyton of the main arm of the Danube [52]. In addition, LPGs are more common in shaded environments [54] and are able to withstand washing out and physical damage, explaining their domination of unstable habitats [27,53].…”

“…In Hungary, the specific pollution sensitivity index (IPS, Coste in Cemagref 1982) has been applied to evaluate the ecological status/potential of the Danube River and its branch systems [65], this index was used alongside the Danube for ecological status assessment [66]. Although the IPS index has been primarily developed for the detection of basic inorganic nutrients and organic loads in water courses, its value is also associated with hydro-morphological changes [52]. Diatoms are also good ecological indicators of the effect of altered hydrological conditions, as they react with great sensitivity not only to chemicals but also to physical conditions [67].…”