Niechwiej A.: Formation of groupings of mayfly larvae (Ephemeroptera) in the area of small hydrological structures, in the streams of the Kamienica Nawojowska river basin (the Sądeckie Beskids, Poland). Ekológia (Bratislava), Vol. 35, No. 4, p. 320-339, 2016. Anthropogenic modification of abiotic factor in turn influencez biotic communities. The aim of this study was to characterise clusters of mayflies in selected streams of Kamienica Nawojowska river basin in conjunction with small, lateral hydrological structures that have been built in this area. There was an attempt to determine whether and to what extent small lateral hydrological structures affect larvae of mayflies in the examined mountain streams. An analysis of the taxonomic composition of mayfly clusters in the examined stream sections was carried out. For this purpose, the author described the taxonomic wealth, variation in the density of organisms, the domination structure within taxonomic groups and trophic functional groups, taxonomic variation (based on the Shannon-Winner factor), constancy of occurrence (according to the Szujecki formula) as well as faunistic similarity (according to the Jaccard formula). An emphasis was also placed on the species included in the Red List of Vulnerable and Endangered Species in Poland (2002). The obtained results indicate a high taxonomic richness and a large diversity of mayfly fauna on the examined stream sections. There were no significant differences, however, in this aspect between posts situated upstream and downstream from the hydrological structures. The formation of clusters was influenced not so much by small hydrological structures as by other abiotic factors such as the nature of the bottom substrate, the way in which the basin is used, the location of a particular post on a particular watercourse section as well as other anthropogenic activities (e.g. those related to forest management). A comparison of the obtained data with the results of the research conducted before the completion of major regulatory works in Kamienica Nawojowska river basin showed that the mayfly fauna had preserved a large taxonomic richness, although some changes had occurred in the structure of the clusters. However, further research related to this issue is needed, especially in other river basins of the Beskids.

The study of larval stoneflies was carried out in the years 2010-2011 in the Kamienica Nawojowska river basin. The study involved three left-bank tributaries of the Kamienica Nawojowska River: the Kryściów, Łabowczański Potok and Homerka streams, in the course of which there were present small transverse hydrological structures. In the streams, within the investigated facilities, a large taxonomic richness of stoneflies was discovered. There were no significant differences in taxonomic richness and abundance of organisms forming stonefly clusters between stations situated upstream and downstream from the small transverse hydrological structures, which do not change the volume of the flow. The shape of the clusters in the studied streams and their individual sections were not as much influenced by the presence of small transverse hydrological structures as by other conditions such as: seasonal occurrence of taxa, similar type and structure of the bottom substrate, the way in which the territory of the basin is used. Assemblages of stoneflies were not significantly depleted after regulatory works, which is confirmed by the comparison with the results of previous years.