engleski

The structure and dynamics of the non-biting midge assemblages (Chironomidae, Diptera) in a dinaric karst river, River Dobra, Croatia

Because of their ubiquity and the large variety of ecological niches in which they exist, the larvae of family Chironomidae are valued as excellent bioindicators. However, the impacts of disturbance events, such as the construction of a hydropowerplant dam, on non-biting midge assemblages were sparsely studied in dinarickarst rivers. The aim of this study was to investigate the temporal dynamics of the chironomid assemblages in the moss microhabitats of the Dobra River before and after new large dam construction. The Dobra is a karstic river situated in the central Croatia, characterized by a subterranean flow and numerous unique microhabitats, including moss-covered substrates which represent a refuge from the fast flowing current and potentially trap for food particles, what makes them preferable habitat by smaller macroinvertebrates. Sampling was conducted in the period from 2007 to 2016, with the notable year of 2010 when the hydroelectric power plant Lešće (HEPP Lešće) was finished 460 m upstream from the sampling site. The samples of moss with accompanying macroinvertebrates, were collected with a hand net (mesh size of 200 μm) and preserved in a 70% alcohol. Before sampling several environmental factors were measured using WTW probes: water temperature, oxygen saturation and concentration, pH and electrical conductivity. Collected organisms were sorted and identified to the lowest possible taxonomic level. Analysis of the chironomid assemblages before and after the dam construction revealed important changes. IndVal analysis indicated species Nilotanypus dubius and Tanytarsus sp. as representative before the construction and Cricotopus gr.tremulusand Orthocladius (Orthocladius) sp. as representative taxa for the period after 2010. Larval abundance was found to have the greatest positive correlation with the oxygen concentration in water, water temperature and pH. Although chironomids have high natural and seasonal variability, which have to be taken into account, the changes of the chironomidassemblage structure after theconstruction of the HEPP, indicates ecological changes of the studied area, since the newly dominant taxa can thrive in the nutrient rich habitats. A dam closure can highly influence the hydrology, temperature regime of the modified water-body and consequently degrade the water quality and influence the benthic organisms.

Chironomid larvae, water quality, HEPP

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