20C3

C. Inland waters

Muddy and sandy river banks with communities of small, annual hygrophytes

Relationships with habitat classifications. EUNIS: C3.431 Ponto-Pannonic riverbank dwarf sedge communities; PAL. CLASS.: 22.32 Euro-Siberian dwarf annual amphibious swards; HD 92/43: 3130 Oligotrophic to mesotrophic standing waters of plains to subalpine levels of continental and Alpine region and mountains areas of other regions with vegetation belong to the Littorelletea uniflorae and/or Isoeto-Nanojuncetea.

Conservation status. BDA, BC, HD.

Category. Endangered [EN – A1,2 C2 D2 E2 F2 G2 H2 J].

General characteristics. The habitat includes riverside pioneer coenoses of small (up to 10 cm high) annual hygrophytes that develop on drying wet deposits of mud and sand during the second half of the summer when the level of the water bodies decreases. They are particularly typical for the alluvial deposits along the Danube and, to a more limited extent, along some of the large inland rivers such as Matitsa, Toundzha, Ogosta, Yantra, and Vit rivers. They also occur sporadically in the periphery of riverside lakes and swamps, on the bottom of dried-out fish ponds and near some large lowland dams with clayey beds and flat banks. These coenoses are dynamic and depend on the low waters of the water bodies. Every year their distribution and time of occurrence change depending upon the water level and the period of drought. They exist for a short period of time, approx. a month, mainly at the end of the summer or in the autumn. These coenoses also strongly depend on the level of humidity, which decreases as the water retreats and hence, different zones develop according to the stages of this process. The over-wet areas are covered by monodominant coenoses of Eleocharis acicularis (association Eleocharidetum acicularis).They usually cover small areas of several square meters. They also develop in the water (about 1 cm high). When the periphery dries up the composition of the coenoses is diversified and it depends on the ground, whether it is muddy and richer in nutrients or sandy and poorer. When the bottom is muddy various coenoses develop. They belong mainly to the association Dichostylido michelianae-Gnaphalietum uliginosi: Dichostylis michelianus (= Cyperus michelianus), Butomus umbellatus, Cyperus fuscus, Echinochloa crus-galli, Eleocharis palustris, Gnaphalium uliginosum, Lindernia dubia, Persicaria lapathifolia, Portulaca oleracea, Rorippa sylvestris.These communities usually make complexes with ruderal coenoses. Very often, in their composition participate also different nitrophilic ruderals, such as Amaranthus albus, A. lividus, Bidens frondosa, Chenopodium album, C. ambrosioides, C. polyspermum, and Xanthium italicum. The coenoses that develop on poorer and sandy deposits are slightly different. Together with the species from the group above some other species, more typical of sandy substrates, also appear: Astragalus contortuplicatus, Crypsis alopecuroides, Cyperus glomeratus, and Glinus lotoides (association Dichostylido-Heleochloetum alopecuroides).On the most elevated parts of the banks the ground is very dense and salination also is observed. Closed halophytic coenoses (Pulicario-Menthetum pulegii) develop there on  large areas. These coenoses are dominated by Agrostis stolonifera, Cynodon dactylon, Inula britannica, Lythrum salicaria, Mentha pulegium, Potentilla anserina, Pulicaria dysenterica, P. vulgaris, Trifolium fragiferum subsp. bonannii. Syntaxonomically all coenoses in this habitat type belong to class Isoeto-Nanojuncetea (alliances Nanocyperion flavescenstis and Verbenion supini).

Characteristic taxa.

Distribution in Bulgaria. Along the Danube, on the Danube bank and islands; along Maritsa, Toundzha, Vit, Yantra and Ogosta rivers. More rarely on the banks of some large lowland dams – e.g. Gorni Dabnik, Pyasachnik, Koprinka; near Plovdiv; on the drying bottom of lakes and swamps (on Persina island in the past as well).

Conservation importance. Some rare and protected species occur in the coenoses on the alluvial river banks such as Dichostylis michelianus (= Cyperus michelianus) and Lindernia procumbens. The fungi species of conservation importance Battarea phalloides and Tulostoma fimbriatum also occur in this habitat. As a result of the natural dynamics, this habitat type is vulnerable and inconstant.

Threats. Extraction of gravel and sand from the river terraces; change in the hydrological regime of the large rivers and natural lakes: drainage, redirection of river beds, changes in the status of many fish ponds, unnatural circulation of the water in the dams, invasion of alien species which change the natural, species structure of the coenoses, erosion, low water level or flooding along the river beds.

Conservation measures taken. The habitat is in Annex № 1 of BDA. Some of the localities are within protected areas – Persina Nature Park, Kalimok – Brashlen Protected Site, Komplex “Aleko-Telika” Protected Site, Ibisha Managed Nature Reserve and sites from the European Ecological Network NATURA 2000.

Conservation measures needed. Study and monitoring of the dynamics of and threats to this habitat type; termination of large-scale hydro-ameliorative activities and the extraction of gravel and sand along the rivers (mainly along the Danube). The localities of this habitat to be included in sites of NATURA 2000.

References. Stojanov 1948; Tzonev 2002; Horvatič 1931.

Author: Rossen Tzonev


Muddy and sandy river banks with communities of small, annual hygrophytes (distribution map)