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04C1

C. Inland waters

Natural or semi-natural mesotrophic to eutrophic lakes and marshes with macrophytic vegetation

Conservation status. BDA, BC, HD.

Category. Endangered [EN – A1, 2 C1 D3 E2 F2 H2 I J L2].

General characteristics. These habitats are mesotrophic to eutrophic lakes and marshes close to the rivers (mostly along Vit, Iskar, Osam, Yantra and Matitza rivers), some of the limans at the Black Sea (at Shabla and Durankulak towns) and lagoons (Arkutino, Alepu swamps). To this group belong also water bodies of partly anthropogenic origin if specific hygrophytic coenoses develop in them, e.g. abandoned and flooded rubble storage places, old river beds, some marshes that were used as fish ponds and consequently abandoned (Orsoya, Pozharevo, Nova Cherna, Mechka marshes). Some of the most important marshes were drained at the beginning of the 20th century, such as Vidin and Belene marshes, Svistovska Balta marsh, Karaboaz marshes (Desna, Vidra and Kraiste marshes) and Kozloduy marshes (Baklitsa and Slana marshes), Vardim marsh, Dzhulyunska rivulet, Straldzha marsh, Sindel (Sultanlar) marsh, Aidemir marsh, etc. Other marshes are with a considerably changed water regime. They dry up in summers and the hydrophytic coenoses almost disappear, such as Ostrov marshes, Kaykusha marsh, the marshes in Persina island (Peschina, Dylyova Bara and Martvo marshes), and Listeva marsh near Garvan village. Other marshes, i.e. the ones near Malak Preslavets village, and Rabisha lake, and Kayabash and Tchoklyovo marshes, have been transformed into dams. The eutrophic and mesotrophic lakes and marshes are mostly muddy, rich in organic substances, and slightly to moderately alkaline – usually pH>7. For instance, the pH of Srebarna Lake varies between 7,5 and 9,5. The mineralization of the water is usually high, the oxygen content varies and particularly in summers oxygen deficiency can be observed in the bottom layers. The depth of the water layer during the active vegetation period is most often between 0,70 and 1,50–2,00 m. In some lakes, with more transparent water, hydrophytic coenoses can develop at 3–4 m. The bottom is sandy to muddy and clayey. As a result of the normal annual circulation, the water of the former Danubian marshes the river used to flow away the decaying plant material, thus opening sandy, alluvial sediments on the bottom. When there is no water current in the lakes, the sediments sometimes reach 1 m or more in thickness (in Srebarna Lake they are up to 2 m). The same was the case with the marshes in Persina island when they were separated from the Danube by dykes. Usually, the hydrophytic coenoses in swamps and lakes make complexes with various hygrophytic communities, e.g. strips or patches of Phragmites australis, Typha spp., Scirpus lacustris (= Schoenoplectus lacustris), tall sedges (Carex spp.) etc. As the lakes and swamps become shallow, they dry up or deposits of plant remnants (turf) accumulate and swamps can be completely taken over. This is a slow, natural process that is speeded up by the human activities. This is a degradation succession of the lakes and swamps that leads to the strong reduction of their role to preserve the hydrophytic flora and fauna.

The hydrophytic communities are very diverse. They often make complexes with other coenoses. Therefore three subtypes have been described here:

1. Vegetation, freely floating on the surface (alliance Lemnion minoris and Hydrocharition). This subtype encompasses the coenoses of Hydrocharis morsus-ranae, Lemna gibba, L. minor, L. trisulca, Salvinia natans, Spirodela polyrhiza, Stratiotes aloides,and Wolffia arrhiza. Most of these species are widely distributed in the lakes, swamps and artificial water bodies (canals, dams), and make different single-species or mixed coenoses. They occur both on the surface (Hydrocharis morsus-ranae, Lemna minor, Ricciocarpus natans, Salvinia natans, Spirodela polyrhiza, Stratiotes aloides, Wolffia arrhiza), and submerged in the water (Lemna trisulca, Riccia fluitans). The coenoses of Stratiotes aloides are very rare. They have been registered only in Srebarna lake and in the large canals near Ostrov village, Vratsa region, and probably are now extinct.

2. Vegetation with floating leaves and rooted (alliance Nymphaeion alba). These are various, typical, hydrophytic coenoses that develop at 1–1,5 (2) m depth in water bodies with muddy bottoms. They are mixed or dominated by Nuphar lutea, Nymphaea alba, Nymphoides peltata, Persicaria amphibia, Potamogeton natans,and Trapa natans. Only the coenoses of Persicaria amphibia and Potamogeton natans are widely distributed.The communities of Nymphoides peltata are ecologically relatively plastic and can develop in more shallow and drying water bodies, fish ponds, large flooded areas, canals. These communities are a degradation stage of the development of typical hydrophytic vegetation. They can replace also the rarer and less adapted coenoses of Nuphar lutea, Nymphaea alba,and Trapa natans when the water bodies become more shallow and with more vegetation in them. The communities of Nuphar lutea are the rarest communities occurring in recent years in several places along the Black Sea coast (Ezerest village, Veleka River), Maitsa River (Popovitsa village) and along the Danube (the former fish ponds near Orsoya village).

3. Submerged vegetation (alliances Magnopotamion and Parvopotamion). These communities occur in deeper and clearer water bodies with mostly sandy or gravel bottoms. They are mixed or dominated by Ceratophyllum demersum, C. submersum, Elodea canadensis, E. nuttallii, Myriophyllum spicatum, M. verticillatum, Najas marina, N. minor, Potamogeton crispus, P. gramineus, P. lucens, P. perfoliatus, P. pusillus, P. trichoides,and Zannichellia palustris.Some of these species are less demanding to the light conditions and can constitute an underwater layer in the coenoses of some of the above-mentioned two vegetation subtypes: e.g. Ceratophyllum demersum and Elodea canadensis. Other species like Myriophyllum spp. and Potamogeton lucens make mostly their own coenoses. Most of the species of this subtype are widely distributed in water bodies of various origins (swamps, lakes, dams, draining canals, fish ponds, etc.). However, the coenoses of species like Potamogeton trichoides, Ceratophyllum submersum, and Najas marina, are rarer and occur only in several localities in the country.

Characteristic taxa.

Distribution in Bulgaria. Throughout Bulgaria, mainly in the lowlands. Such lakes occur mostly in the Danubian plain (along the Danube, Iskar, Vit, and Yantra rivers), Thracian lowland (mainly along Maritsa river) and at the Black Sea coast (some limans and lagoons), up to 500 m alt.

Conservation importance. One of the most important and rich habitats with diverse organisms. A number of rare, endangered and protected plants and animals occur, among which are some typical hydrophytes like Salvinia natans, Wolffia arhiza, Trapa natans, Nymphaea alba, Nuphar lutea, Nymphoides pelatata, Stratiotes aloides, Ricciocarpus natans, and Aldrovanda vesiculosa. The habitat is of ultimate importance for hundreds of species of high conservation concern: fishes – wild carp, umbra; amphibiants – fire-bellied toads, European spadefoot toads, crested tritons; reptiles – water turtles, snakes; birds – gulls, terns, herons, grebes, cormorants, pelicans, diving ducks, ducks, birds of prey, plovers, songbirds, etc.The habitat is a very good trophic basis for different bat species: Mammalia: Chiroptera: Myotis daubentonii, M. capaccinii, Nyctalus noctula, N. leisleri, Eptesicus serotinus, Pipistrellus pipistrellus, including P. nathusii which occurs abundantly in late summers and autumns.

Threats. Draining of the riverside lakes and swamps and hydro-ameliorative activities along the rivers (dyke-building, draining); drying up of the water bodies as a result of the climate aridisation and accumulation of dead plant material; extraction of gravel and sand; pollution with waste waters and household waste; fertilization and using of pesticides in the adjacent arable land; destruction of the riverside forests; use of the lakes and swamps for watering.

Conservation measures taken. The habitat is included in annex № 1 of the national Biodiversity Act. Some of the localities are within existing protected areas: Srebarna Managed Nature Reserve; Persina Nature Park; Garvanski Blata, Malak Preslavets, Shablensko Ezero (lake), Durankulashko Ezero (lake), Kalimok-Brashlen, Ribarnitsi Orsoya and Martvitsata Protected Sites as well as sites from the European Ecological Network NATURA 2000. Projects dedicated to the restoration of the swamps on Persina island and the fish ponds in Kalimok-Brashlen Protected Site have been implemented.

Conservation measures needed. Change of the negative attitude towards swamps, restoration of drained swamps and the improvement of water regime of the existing ones, termination of the hydro-meliorative activities along the rivers.

References. Bonchev 1929; Jordanoff 1931; Kochev & Jordanov 1981; Petkoff 1911; Tzonev 2002.

Authors: Rossen Tzonev, Vladimir Valchev, Valeri Georgiev


Natural or semi-natural mesotrophic to eutrophic lakes and marshes with macrophytic vegetation (distribution map)