Management measures for the restoration of degraded ecosystems in order to increase biodiversity conservation in the Târnava Mică catchment area. Case study Bălăuşeri section, Târnava Mică River, Romania

The paper examines the possibilities of maintaining the longitudinal connectivity of the Târnava Mică R water courses in the context of hydrotechnical works execution. The main reason why the longitudinal connectivity needs to be analysed is that the transverse obstacles may prevent the migration of upstream fish species in order to reproduce the species concerned. In this way, the state of aquatic ecosystems is affected, which the Water Framework Directive aims to protect. The European Commission has launched two infringement procedures against Romania due to the destruction of unique habitats by not ensuring the longitudinal connectivity. The current methodology for the restoration of longitudinal connectivity provides that the longitudinal connectivity of a water body is ensured if there are no transverse obstacles on the river, or if these obstacles meet certain criteria which make the pressure given by them insignificant. In addition, longitudinal connectivity is an important criterion for defining the natural water bodies and heavily modified water bodies. The most widespread measure is the fish scale. The advantage is given by the lowest cost compared to the other variants and the fact that in many cases, it can be applied to the already existing constructions. However, there is a construction height limit for which it is recommended. In the National Administration of Romanian Waters methodology, the height limit is 15 m. The case study in this paper will also present the numerical modelling (1d) for a fish scale at Bălăuşeri on the Târnava Mică water stream from the Mureş River catchment area. The purpose of the case study of the longitudinal connectivity of the Târnava Mică River was to restore water connectivity to ensure favourable conditions for aquatic species dependent on riparian habitats.