Limnological Concept Gesäuse Phase II

This study presents phase II of the two-phase project management for the creation of a Limnological concept for the Gesäuse National Park. The basis for the drafting of the concept is the 6(2) of the National Park Ordinance, which states: The National Park Administration has to draw up a limnological concept and implement it within the framework of fisheries control. On the basis of this concept, the conservation of natural biodiversity and genetic variability, as well as the progress of the hemic animal population, will be ensured and promoted. Already for the processing of phase I of the limnological concept Gesäuse was divided into two investigation areas in which very different actual conditions and requirements for measures exist due to the strongly different proximity of nature or anthropogenic preload. The areas can be characterised as follows: — Investigation area 1 (UG 1): Enns between Lauferbauern and Gstatterbodenbrücke (approximately 6.7 km), Johnsbach from the tunnel in Johnsbach to the mouth of the Enns (approximately 4.7 km) of natural water character, predominantly unmounted or in dismantling as part of the EU-LIFE project. The naturalness of the water is comparatively high here; however, the 9 km long free flow route between the entrance of the Gesäuse and the Gstatterboden storage space also exhibits anthropogenic impairment as a result of spill-water discharges of the power plants at the two feeders Sölkbach (since 1978) and Salza (since 1949). Due to the surge operation of these power plants, the discharge behaviour of the Enns was significantly changed. Even in the Gesäuse, water level fluctuations of up to 20 cm per day (up to about 40 cm when the two spill amplitudes are superimposed) can still be observed (Hohensinner et al. 2008). — Investigation area 2 (UG 2): Enns between Gstatterbodenbrücke and Disc Fishing Bridge west of Hieflau (approx. 8.1 km) severely impaired section of the river: Dam root, reservoir with weir system and subsequent expulsion line (KW Hieflau) The severe anthropogenic impairment of this section is almost entirely due to the congestion and the abstraction of water for the power plant; other hydraulic interventions or morphological changes, such as those prevailing on lowland rivers, play only a small role on the enns in the Gesäuse. Thus, the Enns in the Gesäuse was in a largely natural state until the construction of the Hieflau power plant and the weir near Gstatterboden in 1953. Since commissioning, the Enns has been jammed on an approximately 1.5 km long route and diverted in the weir area, so that the drain is significantly reduced downstream of the weir on the approximately 7 km long discharge line between Gstatterboden and Hieflau (Kummerbrückenstrecke). The storage space has comparatively monotonous shore areas, on the left bank the wooded hem is largely missing. The route has so far been completed in summer (1 April 15. Oct.) dynamically endowed with up to 7.0 m/s, assuming a base dotation of 3.5 m/s. In winter there was no dotation of the expulsion line (Hohensinner et al. 2008). For Phase II, one sample of Enns and Johnsbach was now taken in area 1 and one sample at the Enns in test area 2. In particular, the following work was envisaged, the results of which are documented and discussed in this report: — Surveys of the macrozoobenthos and phytobenthos in Enns and Johnsbach, — Assessment of the ecological status of the two waters under the Water Framework Directive; and — Development of measures to achieve very good ecological status.