Biologia 72/6: 652—670, 2017 Section Zoology DOI: 10.1515/biolog-2017-0077 Downstream eﬀect of a pumped-storage hydropower plant on river habitat conditions and benthic life – a case study Igor Kokavec 1,5 , Tomáš Navara 1 , Pavel Beracko 1 ,Tomáš Derka 1 , Ivana Handanovičová 1 , Andrea Rúfusová 1 , Zuzana Vráblová 2 , Tomáš Lánczos 3 , Marta Illyová 4 & Ferdinand Šporka 5 1 Department of Ecology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, SK-84215 Bratislava, Slovakia; e-mail: kokavec@fns.uniba.sk 2 Water Research Institute, Nábrežie arm. gen. L. Svobodu 7, SK-81249 Bratislava, Slovakia 3 Department of Geology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, SK-84215 Bratislava, Slovakia 4 Plant Science and Biodiversity Centre, Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84523 Bratislava, Slovakia 5 Institute of Zoology, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84506 Bratislava, Slovakia Key words: benthic invertebrates; pumped-storage hydropower plant; longitudinal discontinuum; secondary production; life history Abstract: In spite of many investigations about the impact of reservoirs on river continuum, the downstream eﬀects of a pumped-storage hydropower plants (PSHP) still have been less known. The aim of the study was to evaluate the downstream eﬀect of the PSHP Čierny Váh in regard to the Serial Discontinuity Concept assumptions or studies assessing more frequent types of hydropower reservoirs. We predicted that the increase of water temperature and the alteration of food sources will hierarchically be the most relevant factors determining macroinvertebrate community composition. We focused on mayﬂies, caddisﬂies and non-insect benthic invertebrates due to their appropriate responses to discontinuity. We also determined the inﬂuence of the hydropower plant on life cycles and productions of the most abundant species of mayﬂies and caddisﬂies. We recorded the unique eﬀect of the PSHP Čierny Váh on its downstream environmental variables. According to the nested ANOVA results, temperature regime, transported organic matter, benthic ﬁne particulate organic matter and periphyton biomass were the environmental variables signiﬁcantly modiﬁed by the river discontinuum. Signiﬁcant diﬀerences were also found in the case of macroinvertebrate species richness, density and diversity. Nevertheless, based on the forward selection test for predictor eﬀects, none of the environmental variables aﬀected the macroinvertebrate assemblages signiﬁcantly. However, the redundancy analysis revealed a separated group of macroinvertebrates preferring conditions characteristic for the site immediately below the reservoir. Regarding the impact of the reservoir on life histories, we revealed the shift in hatching, emergence and duration of life cycles of the abundant mayﬂies (except Baetis rhodani) and caddisﬂy Ecclisopteryx dalecarlica. Total annual production of mayﬂies as well as caddisﬂies was several times higher at the site immediately below the reservoir. Although PSHP Čierny Váh matches the SDC assumptions (except thermal stratiﬁcation), the downstream impact resembles much more the eﬀects of small reservoirs or epilimnetic-release reservoirs. Introduction The downstream eﬀects of large, thermally stratiﬁed reservoirs releasing hypolimnetic water, in other words matching the speciﬁcations of the Serial Discontinuity Concept (SDC) (Ward & Stanford 1983, 1995; Stanford & Ward 2001), have been assessed by many scientiﬁc papers. The SDC is a theoretical framework describing environmental and biological changes in river contin- uum (sensu Vannote et al. 1980) induced by reservoirs. Generally, studies support the SDC predictions in spite of formal testing (Ellis & Jones 2013). Additionally, there have been studies of diﬀerent types of reservoirs, e.g., epilimnic-release reservoirs (Fraley 1979; Lessard & Hayes 2003), mixed-release reservoirs (Armitage 1978, 2006), small hydropower plants (Svitok & Novikmec 2014; Beracko et al. 2016) and pumped-storage hy- dropower plants (Šubrtová & Tuša 2005) that do not meet some of the SDC speciﬁcations. In headwaters, the prediction of the SDC in the case of organic and inorganic matter transport disrup- tion has often been conﬁrmed (e.g., Webster et al. 1979; Voelz & Ward 1991). The reduction in sediment load that is deposited in the reservoir can lead to down- stream channel degradation and substrate armouring due to erosive power of the river ﬂow (Donnely 1993). Moreover, the damming of headwaters induces a shift in the photosynthesis/respiration ratio (Ward & Stan- ford 1983) by the development of periphyton immedi- ately below the reservoir (Morley et al. 2008; Katano et al. 2009; Rehn 2009). Even though, an opposite pattern was observed below a hydropeaking reservoir c 2017 Institute of Zoology, Slovak Academy of Sciences Brought to you by | University of Sussex Library Authenticated Download Date | 9/26/17 2:34 PM