Assessment of the ecological functionality of anthropogenically created habitats in the impoundment of the hydropower plant Freudenau (Vienna, Austria) with bi- and multivariate statistical analyses

ZOOLOGIA 27 (1): 92–98, February, 2010 Assessment of the ecological functionality of anthropogenically created habitats in the impoundment of the hydropower plant Freudenau (Vienna, Austria) with bi- and multivariate statistical analyses Martin Tarkus1; Christian Volkmann1; Silke-Silvia Drexler2; Herwig Waidbacher2 & Michael Straif2 1 Postgraduate program of Applied Hydrobiology and Bioengeneering, Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Applied Life Sciences, Vienna. Max – Emanuel-Strasse 17, 1180 Wien, Austria. E-mail: ; 2 Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Applied Life Sciences, Vienna. Max – Emanuel-Strasse 17, 1180 Wien, Austria. E-mail: ; ; ABSTRACT. The construction of the hydropower plant Freudenau was accompanied by the introduction of new structures and habitats. This study processes and evaluates the ecological fish data for the periods 1999/2000 and 2003/ 2004. The area was subdivided into five sections and 19 habitats (stream kilometer 1914.50 to 1994.60). Bi- and multivariate analyses were inducted with SPSS© (SPSS 2007). The CPUE values show that most fish remain in the Transition Zone and in the Head of Reservoir. The cluster analyses of the individual habitats show that these can be characterized primarily by abiotic factors. There was a strong statistical relationship between the individual habitats and the Danube mainstream. We conclude that fish have access to the habitats and that there is interconnectivity between these habitats. In general, the habitats were highly accepted by the fish species: all contained both juvenile and adult fish. The differentiated spectrum of species points to complex relationships. In principle the newly created habitats can be considered to be good replacement environments. KEY WORDS. Aquatic ecosystems; fish ecology; hydraulic engineering; river management. In potamal rivers, hydropower plants represent special ecological problems. The low descent requires large-dimensioned impoundments. Monotonous habitats arise both in the retention areas and tailwaters. Hinterland detachment and groundwater isolation impair the riparian forest. Key features include the reduction of dynamic processes, such as one-sided directional developments, which are expressed as degradation and obsolescence of the vegetation. The river bed erosion related to bed load retention represents another problem (JUNGWIRTH et al. 2003). Originally, the Danube in the Vienna area was a braided river system with numerous mainstreams and tributaries. The regulation in the 19th century, however, created a single river mainstream. The typical fish fauna is therefore confined to the main arm of the river. The regulation increased flow velocity and river bed erosion, leading to a dominance of rheophilic fish species (WAIDBACHER et al. 1996). During the construction of the hydropower plant Freudenau, structures and habitats were created and a bypass channel was built according to the requirements of the European Water Framework Directive. This was preceded by research by the Institute of Hydrobiology and Aquatic Water Management, University for Natural Resources and Applied Life Sciences, into the ecological preservation in the area of hydropower plant Freudenau (WAIDBACHER et al. 1996). Both benthic long-term relationships and the fish biocenosis were studied. The study focused on the fish ecological conditions. Due to their various ecological requirements, fish species are excellent indicators for hydromorphological changes; this is decisive in assessing the freshwater ecology and especially the ecological functionality. Accordingly, fish are crucial indicators for continuum conditions and for habitat structures (SCHMUTZ et al. 2000). The ecological functionality is the ability to maintain the ecological integrity between waters and the occurrence of organisms in the surrounding area, according to the natural characteristics of the respective water body type (A DMICKA et al. 1992). This study evaluates the fish ecological functionality of anthropogenic shore structures related to the temporal gradient at the hydropower plant Freudenau. © 2010 Sociedade Brasileira de Zoologia | www.sbzoologia.org.br | All rights reserved. Assessment of the ecological functionality of anthropogenically created habitats MATERIAL AND METHODS The hydropower plant Freudenau, built between 1992 and 1998, was the first large, modern power plant ever built in a major city. For a detailed investigation, the study area (stream kilometer 1914.50 to 1994.60) was divided into five sections (G INZLER 2002). Each section contains various habitat structures located on the left river side. The five river sections are: Tailwater (strkm. 1914.50 to 1921.05), Impoundment (strkm. 1921.05 to 1928.00), Transition Zone (strkm. 1928.00 to 1935.00), Head of Reservoir (strkm. 1935.00 to 1945.50) and Free Flowing Stretches (strkm. 1945.50) (Fig. 1). During the construction of the power plant, nine artificial habitats (A-I) were installed on the left river bank to simulate tributaries and bays. Habitat A (strkm. 1921.90 to strkm. 1922.40), B (strkm. 1923.90 to strkm. 1924.50), C (strkm. 1926.20 to strkm. 1926.70) and D (strkm. 1927.35 to strkm. 1927.50) are situated in the Impoundment. The Transition Zone encompasses habitats E (strkm. 1928.80 to strkm. 1928.90), F (strkm. 1929.90 to strkm. 1930.10) and G (strkm. 1930.90 to strkm. 1931.10). The Head of Reservoir is characterized by the habitat H (strkm. 1932.20 to strkm. 1932.50) and I (strkm. 1934.80 to strkm. 1935.50). 93 E-fishing creates an electric, externally applied DC field in the water to which fish react. Individuals in the electric field lines actively swim to the anode and are narcotized (electrotype narcosis). The efficiency and domain of this method depend on the conductivity of the water. E-fishing is a quantitative and species-selective fishing technique (COWX & LAMARQUE 1990). The captured fish were determined on the spot, measured and weighed. Those individuals that could not be determined (primarily juveniles) were fixed in a 4% formalin solution and later examined under a stereomicroscope. In most cases the sampling unit of the “CPUE” (Catch Per Unit Effort) was determined by the number of individuals per ten minutes of fishing. The fish ecological data from 1999 to 2000 as well as from 2003 to 2004 were processed, evaluated and analyzed with multivariate statistical methods. The data collected formed the Access databases “Freudenau” (1999/2000) and “FIDON” (2003/2004) of the Institute for Hydrobiology and Aquatic Ecosystem Management. They were further subjected to bi- and multivariate analyses and their temporal course evaluated. The E-fishing data were used to obtain values for an efficient statistical evaluation with binary data, frequencies and ”Catch Per Unit Effort” (CPUE). SPSS 16.0 was used for the (...truncated)