Limnological concept Gesäuse Phase II

The present study represents the phase II of the two-phase project execution for the preparation of a Limnological Concept for the Gesäuse National Park. The basis for the development 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 fishing regulations. On the basis of this concept, the preservation of natural biodiversity and genetic variability as well as the advancement of the native animal population is to be ensured and promoted. Already for the processing of Phase I of the Limnological Concept Gesäuse, a division into two study areas was carried out, in which very different actual states and measures are required due to the very different proximity to nature or anthropogenic pre-load. The areas can be characterised as follows: - Study area 1 (UG 1): Enns between Lauferbauern- and Gstatterbodenbrücke (approx. 6.7 km), Johnsbach from the tunnel in Johnsbach to the mouth of the Enns (approx. The degree of naturalness of the water is comparatively high here; however, the approximately 9 km long free flow route between the Gesäuse entrance and the Gstatterboden storage space also shows an anthropogenic impairment as a result of surge water levies from 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, there are still fluctuations in water levels due to swarms of up to more than 20 cm daily (up to about 40 cm if the two Schwallamplituden are superimposed) (HOHENSINNER et al. 2008). - Study area 2 (UG 2): Enns between Gstatterbodenbrücke and Scheibenfischerbrücke west of Hieflau (approx. 8.1 km) severely affected section of the river: Reservoir root, reservoir with defence system and subsequent discharge line (KW Hieflau) The severe anthropogenic impairment of this section is almost entirely due to the congestion and water abstraction of the discharge power plant; Other hydrological interventions or morphological changes, such as those occurring on lowland rivers, play only a minor role at the Enns in the Gesäuse. Thus, the Enns in the Gesäuse were in a largely natural state until the construction of the Hieflau power plant and the Wehres near Gstatterboden in 1953. Since commissioning, the Enns has been dammed on a 1.5 km long route and discharged in the weir area, so that the runoff from the weir on the approximately 7 km long discharge route between Gstatterboden and Hieflau (Kummerbrückenstrecke) is significantly reduced. The storage space has comparatively monotonous shore areas, on the left bank the woody hem is largely missing. The discharge route has so far been completed in the summer (1 April 15). Oct.) dynamically endowed with up to 7.0 m/s, assuming a base endowment of 3.5 m/s. In winter there was no provisioning of the discharge line (HOHENSINNER et al. 2008). For phase II, one sample was taken at Enns and one sample at Johnsbach in study area 1, and one sample at Enns in study area 2. In particular, the following work was planned, the results of which are documented and discussed in this report: - surveys of 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.