14C2
Slow-flowting rivers without macrophytic vegetation
Relationships with habitat classifications. EUNIS: C2.3 Permanent non-tidal, slow, smooth flowing watercourses, C2.34 Eutrophic vegetation of slow-floating rivers; PAL. CLASS.: 24.1 Part of rivers and streams.
Conservation status. None.
Category. Endangered [EN – C2 D2 E2 F1 G2 H2 J L3].
General characteristics. These are small parts from the middle and low parts of the river valleys of Iskar river (the lowest part where the riverbed has been changed), Osam river (just before it flows into the Danube), Arda river (between Studen Kladenets and Ivailovgrad dams) and the Bulgarian bank of the Danube and its islands. This habitat type occurs at 300–400 m alt. The rivers are slow, the waters are mainly mesotrophic and rarely eutrophic. The highest water level is at the end of spring and the beginning of summer (May - June), and the minimum is at the end of the summer / beginning of autumn (August - October). The depth of the rivers is usually about 1.5 m, sometimes more. The oxygen content changes according to different factors – flow speed, water temperature, etc. The banks and the bottom are muddy (the Danube, Osam river), sometimes gravel-sandy (other rivers). It is typical that in such places the riverbanks are steep and the depth quickly increases. Often these are places of the riverbanks that have been radically changed. That is the main reason why no macrophytic communities or even temporary plant groups develop in these places. In isolated places on the periphery of the river basins, where the flow is slow, small accumulations of Lemna minor can develop. They are temporary and strongly dependent on the water turbulence. Sometimes small groups or single plants of Myriophyllum spicatum, Ceratophyllum demersum, Potamogeton crispus or P. nodosus can occur in such places and they are mostly brought by the river flow. In the riverside area, where the underground waters are high, communities with Berula erecta, Lycopus europaeus, Lythrum salicaria, Mentha aquatica, M. pulegium, Typha angustifolia, T. latifolia, sometimes Sparganium erectum and more rarely Butomus umbellatus develop. Usually, in these places there are also small riverside forests of different willow species.
Characteristic taxa.
- Vascular plants: Ceratophyllum demersum, Lemna minor, Myriophyllum spicatum, Potamogeton crispus, P. nodosus.
- Animals: Crustacea: Acanthocyclops robustus, Canthocamptus staphylinus, Cyclops strenuus, Diacyclops bicuspidatus, D. bisetosus, D. crassicaudis, Eucyclops serrulatus, Megacyclops viridis, Paracyclops fimbriatus.
Distribution in Bulgaria. Different parts of the middle and low river flow of the Danube, Voinishka, Ogosta, Iskar, Osam, Vit, Yantra, Kamchiya, Arda, Maritsa, Struma rivers.
Conservation importance. This habitat type has been strongly changed by man as a result of different hydro-technological activities. The bats Nyctalus noctula, Myotis daubentonii, M. capaccinii, Pipistrellus pipistrellus, P. pygmaeus show high trophic activity above the water surface.
Threats. Hydro-meliorative and hydro-technical activities along the rivers: construction of dykes, draining, water power stations, extraction of inert materials from the rivers, pollution with waste waters and household wastes.
Conservation measures taken. Parts of the habitat are within sites from the European Ecological Network NATURA 2000.
Conservation measures needed. Limitation of the hydro-meliorative activities and the extraction of inert materials along the rivers.
References. Uzunov et al. 1993.
Authors: Vladimir Valchev, Valeri Georgiev
