16C2
Estuaries
Relationships with habitat classifications. EUNIS: X01 Estuaries; PAL. CLASS.: 13.2 Estuaries; HD 92/43: 1130 Estuaries.
Conservation status. BDA, BC, HD.
Category. Critically endangered [CR – A1, 2 C3 D3 E2 F2 G2 H2 I J L2].
General characteristics. This habitat type encompasses the lowermost parts of the rivers where they flow into the sea and are characterized by reduced salinity and increased quantities of organic substances. The typical zonation that is a result of the periodical impact of the tidal flows is absent in the estuaries at the Black Sea. The hydrological conditions vary but there is a distinct gradient of the hydro-chemical parameters at the transition from fresh to sea water environment. The water level of the rivers has great impact (seasonal or as a result of the climatic conditions) on the estuaries. Depending upon this, the conditions in the estuaries can vary from fresh water (in spring high-water period) to slightly saline (brackish) where the water is mixed. When the water level is low (in summers) stable stratification occurs in the estuaries when fresh waters run above the denser, salty waters of the sea.
The slow flow of the rivers causes the accumulation of fine deposits, hence they are structurally dynamic units. Very often they are barred partially or completely by sand strips that are wiped away by the spring high waters. The complex impact of the hydro-chemical gradients, the accumulation of sediments and the formation of sand strips and muddy areas are the prerequisites for the development of marshy vegetation (communities of Phragmites australis, Typha spp., Bolboschoenus maritimus) and of abundant water vegetation in the shallow areas (Potamogeton spp., Myriophyllum spp., Zannichellia palustris, Lemna spp.). Therefore the estuaries are among the most productive habitats on the earth. Due to the dynamic conditions of these areas, typical marine organisms can enter the rivers and river organisms can live in the habitats where the river flows into the sea and the water is less salty. The estuaries make complexes with the surrounding coastal terrestrial vegetation – dunes, riverside and longoz forests, etc. Hence their importance for the preservation of the coastal ecosystems increases significantly.
Characteristic taxa.
- Plants: algae – Chara spp., Cladophora spp., Enteromorpha spp.; vascular plants – Bolboschoenus maritimus, Carex spp., Lemna spp., Myriophyllum spp., Phragmites australis, Potamogeton spp., Ruppia maritima, Scirpus litoralis (= Schoenoplectus litoralis), Typha spp., Zannichellia palustris, Zostera marina.
- Animals: invertebrates: Mercierella enigmatica, Upogebia spp., Nereis diversicolor, Jaera sarsi, Leander spp., Loxoconcha spp., Mytilus spp., Cardium edule, Cordylophora caspia, fish: Mugil cephalus, Alosa caspia, Gasterosteus aculeatus, Pungitius platygaster, Syngnathus typhle,birds: Athya nyroca, Haliaetor pygmeus, Ixobrychus minutus, mammals: Lutra lutra.
Distribution in Bulgaria. Black Sea coast, mainly to the South: the estuaries of Kamchiya, Ropotamo, Veleka, Dyavolska, Karaagach, Silistar, Butamyata rivers.
Conservation importance. The estuaries are rich in biodiversity. They are important places for feeding, wintering and reproduction of many fish and birds species. The marshy regions of the Kamchia River estuary are the locality of rare zooplankton species in Bulgaria such as Camptocercus rectirostris, Leydigia acanthocercoides, Microcyclops bicolor and Pleuroxus trigonelus.
Threats. Changes in the water level of the rivers (construction of dams, redirection of the water, etc.) prolong the period of stratification of the estuaries and cause the formation of an anaerobic layer on their bottom. The flow of municipal and industrial wastewater into the estuaries cause eutrophication, accumulation of persistent pollutants in the sediments and therefore contamination of the food chain. Land-use practices in the water catchment areas (deforestation, intensive use of mineral fertilizers and pesticides) cause accumulation of deposits in the estuaries as a result of increased erosion and eutrophication. Introduction of alien and invasive species is also observed.
Conservation measures taken. The habitat is in Annex № 1 of BDA. Some of the estuaries are within existing protected areas – Kamchiya and Ropotamo Strict Nature Reserves, Silistar and Ustieto na Reka Veleka Protected Sites within Strandzha Nature Park, and in sites from the European Ecological Network NATURA 2000. Ropotamo River is a part from a site of the Ramsar Convention.
Conservation measures needed. Protection of the estuaries and elaboration of programs for the management of the water catchments of the respective that will include measures to protect the terrestrial coastal ecosystems near the estuaries. Decrease of the pointsource and diffuse pollution in the water catchments. Protection and restoration of the coastal habitats and the related wetlands. Restoration and maintenance of the natural or close to the natural flow mode of the rivers.
References. Dimitrova-Konaklieva 2000; Kolarov et al. 1978; Kochev & Jordanov 1981; Marinov 1990.
Authors: Ivan Traykov, Plamen Ivanov
