15C2
Slow-flowing rivers with macrophytic vegetation
Relationships with habitat classifications. EUNIS: C2.33 Mesotrophic vegetation of slow-flowing rivers, C2.34 Eutrophic vegetation of slow-flowing rivers; PAL. CLASS.: 22.43 Mesotrophic river vegetation, 22.44 Eutrophic river vegetation HD 92/43: 3260 Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation.
Conservation status. BDA, BC, HD.
Category. Endangered [EN – A1, 2 C2 D2 E2 F1 G2 H2 J L3].
General characteristics. The habitat encompasses the middle and lower parts of large rivers in the lowlands from 0 up to 400–500 m alt. These are mainly Ogosta, Vit, Yantra, Maritsa, Toundzha rivers. The river flow is slow and the waters are mainly meso- to eutrophic. Their maximum is usually in April – June and the minimum is in August – October. The rivers are 0,30–1,50 m deep. The oxygen content is highly variable, and depends on the flow speed, the presence of photosynthesizing organisms and seasonal temperature amplitudes of the water. The bottom is clayey or muddy-clayey, more rarely it is gravel-sandy. Mud deposits accumulate mainly in the river widenings where a number of macrophytes grow – Ceratophyllum demersum, Myriophyllum spicatum, Potamogeton crispus, P. nodosus, P. perfoliatus, Ranunculus trichophyllus,and Zannichellia palustris.Near the banks and in the widenings where the flow is slow coenoses of Berula erecta, Elodea canadensis, Lemna minor, Mentha aquatica, Sagittaria sagittifolia, Sparganium erectum, Spirodela polyrhiza,and Typha latifolia occur. In some of the more polluted and eutrophic rivers like Yantra and Ogosta the quantity of macrophytic vegetation increases.
Characteristic taxa.
- Plants: Algae – Batrachospermum spp., Chantransia spp., Hildenbrandia rivularis, Lemanea spp., Thorea ramosissima; vascular plants – Berula erecta, Butomus umbellatus, Callitriche cophocarpa, Groenlandia densa, Myriophyllum spicatum, Najas marina, Potamogeton crispus, P. pectinatus, P. perfoliatus, P. trichoides, Ranunculus aquatilis, R. penicillatus, R. trichophyllus, Sagittaria sagittifolia, Sparganium erectum, Zannichellia palustris;mosses – Fontinalis antipyretica.
- Fungi: Micromycetes – Ascochyta vollubilis, Erysiphe betae, Septoria polygonorum (on Persicaria hydropiper), Podosphaera xanthii, Puccinia xanthii (on Xanthium italicum), Uromyces rumicis (on Rumex palustris).
- Animals: Crustacea – Acanthocyclops robustus, Attheyella crassa, Canthocamptus staphylins, Diacyclops bisetosus, D. crassicaudis, Eucyclops serrulatus, Limocamptus dacicus, Megacyclops viridis.
Distribution in Bulgaria. The middle and low parts of the large rivers in the Danubian plain, Thracian Lowland, Toundzha Hilly Country and Forebalkan, partly in Strandzha Mts. (Veleka river).
Conservation importance. Some endangered macrophytes occur in this habitat such as Groenlandia densa, etc. The bats Nyctalus noctula, Myotis daubentonii, M. capaccinii, Pipistrellus pipistrellus, and Hypsugo savii show high trophic activity above the water surface.
Threats. Hydro-meliorative and hydro-technological activities along the rivers: construction of dykes, draining, water power stations, extraction of inert materials form the rivers, pollution with waste waters and household wastes, use of pesticides and fertilisers in the neighbouring arable lands, erosion, blocking of the river bed by various deposits, floods and changes in the erosion basis.
Conservation measures taken. The habitat is in Annex № 1 of BDA. Some of the rivers are within protected areas: Veleka River is within Strandzha Nature Park, etc. Vit, Ogosta, Yantra, Toundzha, Maritsa and Veleka rivers are in sites from the European Ecological Network NATURA 2000.
Conservation measures needed. Limitation of the hydro-meliorative activities along the rivers, restoration of the old river beds, and termination of the extraction of inert materials form the river beds within the areas of the protected Natura 2000 sites.
References. Tzonev 2002.
Authors: Rossen Tzonev, Vladimir Valchev
