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108-596: The modern Danube Delta began to form after 4000 BC in a bay of the Black Sea when the sea rose to its present level. A sandy barrier blocked the Danube bay where the river initially built its delta. Upon filling the bay with sediment , the delta advanced outside this barrier-blocked estuary after 3500 BC, building several successive lobes: the St. George I (3500–1600 BC), the Sulina (1600–0 BC),

216-514: A halocline that stops at the Cold Intermediate Layer (CIL). This layer is composed of cool, salty surface waters, which are the result of localized atmospheric cooling and decreased fluvial input during the winter months. It is the remnant of the winter surface mixed layer. The base of the CIL is marked by a major pycnocline at about 100–200 metres (330–660 ft), and this density disparity

324-435: A piezometer . Aquifers are also described in terms of hydraulic conductivity, storativity and transmissivity. There are a number of geophysical methods for characterizing aquifers. There are also problems in characterizing the vadose zone (unsaturated zone). Infiltration is the process by which water enters the soil. Some of the water is absorbed, and the rest percolates down to the water table . The infiltration capacity,

432-459: A decrease in the flux of silicon associated with advection across isopycnal surfaces. This phenomenon demonstrates the potential for localized alterations in Black Sea nutrient-input to have basin-wide effects. Hydrological Hydrology (from Ancient Greek ὕδωρ ( húdōr )  'water' and -λογία ( -logía )  'study of') is the scientific study of

540-492: A dense network of shallow channels in the delta over the same period, a sedimentation enhancing strategy , attenuated the deficit on the delta plain but increased erosion along the coast The Danube Delta is a low alluvial plain , mostly covered by wetlands and water. It consists of an intricate pattern of marshes, channels, streamlets and lakes. The average altitude is 0.52 m, with 20% of the territory below sea level, and more than half not exceeding one meter in altitude. Dunes on

648-759: A different literal meaning (see below), is still widely used: The Black Sea is one of four seas named in English after common color terms – the others being the Red Sea , the White Sea and the Yellow Sea . The earliest known name of the Black Sea is the Sea of Zalpa, so called by both the Hattians and their conquerors, the Hittites . The Hattic city of Zalpa was "situated probably at or near

756-484: A marked vertical stratification and a warm, shallow mixed layer. Day length and insolation intensity also control the extent of the photic zone . Subsurface productivity is limited by nutrient availability, as the anoxic bottom waters act as a sink for reduced nitrate , in the form of ammonia . The benthic zone also plays an important role in Black Sea nutrient cycling, as chemosynthetic organisms and anoxic geochemical pathways recycle nutrients which can be upwelled to

864-846: A mixture of reed roots, grass and soil, usually floating or anchored to the riverbed. As a rule, the reed surrounds the lakes and ponds, and slowly invades the water surface. This type of ecosystem is noted for its variety and large population of birds, some of them are very rare. The most important are the tufted duck ( Aythya fuligula ), red-crested pochard ( Netta rufina ), mallard ( Anas platyrhynchos ), greylag goose ( Anser anser ), pygmy cormorant ( Microcarbo pygmeus ), purple heron ( Ardea purpurea ), great white egret ( Egretta alba ), little egret ( Egretta garzetta ), Eurasian spoonbill ( Platalea leucorodia ), great white pelican ( Pelecanus onocrotalus ), Dalmatian pelican ( Pelecanus crispus ), mute swan ( Cygnus olor ), and glossy ibis ( Plegadis falcinellus ). A recent and welcomed newcomer

972-402: A more global approach to the understanding of the behavior of hydrologic systems to make better predictions and to face the major challenges in water resources management. Water movement is a significant means by which other materials, such as soil, gravel, boulders or pollutants, are transported from place to place. Initial input to receiving waters may arise from a point source discharge or

1080-451: A prediction in practical applications. Ground water is water beneath Earth's surface, often pumped for drinking water. Groundwater hydrology ( hydrogeology ) considers quantifying groundwater flow and solute transport. Problems in describing the saturated zone include the characterization of aquifers in terms of flow direction, groundwater pressure and, by inference, groundwater depth (see: aquifer test ). Measurements here can be made using

1188-561: A series of works to help navigation. In 1878, following the defeat of Ottoman Empire by Russia and Romania, the border between the two countries was set by the Kilia and Old Stambul Channels. In 1991, the Romanian part of the Danube Delta became part of UNESCO 's list of World Heritage Sites . Around 2,733km of the delta are strictly protected areas. In 1998, under UNESCO's Programme on Man and

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1296-467: A single body for several kilometers after the separation from the Chilia. At the mouths of each channel gradual formation of new land takes place, as the delta continues to expand. (Saint George) Chilia , in the north, the longest, youngest, and most vigorous, with two secondary internal deltas and one microdelta in full process of formation at its mouth (to Ukraine). Sulina , the central and thus

1404-569: A strongly stratified vertical structure. Because of the extreme stratification, it is classified as a salt wedge estuary . Inflow from the Mediterranean Sea through the Bosporus and Dardanelles has a higher salinity and density than the outflow, creating the classic estuarine circulation. This means that the inflow of dense water from the Mediterranean occurs at the bottom of the basin while

1512-433: A threat to health—and perhaps even life—for people living on the Black Sea coast. There have been isolated reports of flares on the Black Sea occurring during thunderstorms, possibly caused by lightning igniting combustible gas seeping up from the sea depths. The Black Sea supports an active and dynamic marine ecosystem, dominated by species suited to the brackish , nutrient-rich, conditions. As with all marine food webs,

1620-488: A very different ecosystem called beforedelta . Musura Gulf, north of Sulina, and Saint George Gulf are considered the most representative of this type of ecosystem. Situated on major migratory routes, and providing adequate conditions for nesting and hatching, the Danube Delta is a magnet for birds from six major ecoregions of the world, including the Mongolian, Arctic and Siberian. There are over 320 species of birds found in

1728-516: A very thick convective bottom layer. The Black Sea undersea river is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea. The discovery of the river, announced on August 1, 2010, was made by scientists at the University of Leeds and is the first of its kind to be identified. The undersea river stems from salty water spilling through

1836-443: A weaker mixed assemblage of community development below the seasonal thermocline during summer months, and surface-intensified autumn production. This pattern of productivity is augmented by an Emiliania huxleyi bloom during the late spring and summer months. Since the 1960s, rapid industrial expansion along the Black Sea coastline and the construction of a major dam on the Danube have significantly increased annual variability in

1944-442: Is a current of particularly saline water flowing through the Bosporus Strait and along the seabed of the Black Sea, the first of its kind discovered. Current names of the sea are usually equivalents of the English name "Black Sea", including these given in the countries bordering the sea: Such names have not yet been shown conclusively to predate the 13th century. In Greece , the historical name "Euxine Sea", which holds

2052-507: Is about 1,175 km (730 mi). Important cities along the coast include (clockwise from the Bosporus ) Burgas , Varna , Constanța , Odesa , Sevastopol , Novorossiysk , Sochi , Poti , Batumi , Trabzon and Samsun . The Black Sea has a positive water balance , with an annual net outflow of 300 km (72 cu mi) per year through the Bosporus and the Dardanelles into

2160-402: Is affected by the interaction of dissolved oxygen with organic material and various chemical transformations that may take place. Measurements of water quality may involve either in-situ methods, in which analyses take place on-site, often automatically, and laboratory-based analyses and may include microbiological analysis . Observations of hydrologic processes are used to make predictions of

2268-496: Is also present on the higher grounds of the continental levees , where xerophile ecosystems have developed. Between the aquatic and terrestrial environments is interposed a swampy, easily flooded strip of original flora and fauna, with means of adaptation to water or land, depending on the season or hydrological regime. At the contact between freshwater and sea water, some special physical, chemical and biological processes take place, which have led biologists to consider this area as

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2376-769: Is an important part of the water cycle. It is partly affected by humidity, which can be measured by a sling psychrometer . It is also affected by the presence of snow, hail, and ice and can relate to dew, mist and fog. Hydrology considers evaporation of various forms: from water surfaces; as transpiration from plant surfaces in natural and agronomic ecosystems. Direct measurement of evaporation can be obtained using Simon's evaporation pan . Detailed studies of evaporation involve boundary layer considerations as well as momentum, heat flux, and energy budgets. Remote sensing of hydrologic processes can provide information on locations where in situ sensors may be unavailable or sparse. It also enables observations over large spatial extents. Many of

2484-464: Is connected to the Sea of Azov by the Kerch Strait . The water level has varied significantly over geological time. Due to these variations in the water level in the basin, the surrounding shelf and associated aprons have sometimes been dry land. At certain critical water levels, connections with surrounding water bodies can become established. It is through the most active of these connective routes,

2592-489: Is only one of many important aspects within those fields. Hydrological research can inform environmental engineering, policy , and planning . Hydrology has been subject to investigation and engineering for millennia. Ancient Egyptians were one of the first to employ hydrology in their engineering and agriculture, inventing a form of water management known as basin irrigation. Mesopotamian towns were protected from flooding with high earthen walls. Aqueducts were built by

2700-580: Is subject to interannual variability. Outside of the Rim Current, numerous quasi-permanent coastal eddies are formed as a result of upwelling around the coastal apron and "wind curl" mechanisms. The intra-annual strength of these features is controlled by seasonal atmospheric and fluvial variations. During the spring, the Batumi eddy forms in the southeastern corner of the sea. Beneath the surface waters—from about 50 to 100 metres (160 to 330 ft)—there exists

2808-558: Is the pheasant ( Phasianus colchicus ). Among the mammals, there is the Eurasian otter ( Lutra lutra ), European mink ( Mustela lutreola ), little ermine ( Mustela erminea aestiva ), wild boar ( Sus scrofa ), and wild cat ( Felis silvestris ), in winter the European hare ( Lepus europaeus ) and, on the brink of disappearing from the delta, the wolf and the fox. During the Middle Ages,

2916-454: Is the major mechanism for isolation of the deep water. Below the pycnocline is the Deep Water mass, where salinity increases to 22.3 PSU and temperatures rise to around 8.9 °C (48.0 °F). The hydrochemical environment shifts from oxygenated to anoxic, as bacterial decomposition of sunken biomass utilizes all of the free oxygen. Weak geothermal heating and long residence time create

3024-521: Is therefore anoxic . This anoxic layer is responsible for the preservation of ancient shipwrecks which have been found in the Black Sea, which ultimately drains into the Mediterranean Sea , via the Turkish Straits and the Aegean Sea. The Bosporus strait connects it to the small Sea of Marmara which in turn is connected to the Aegean Sea via the strait of the Dardanelles . To the north, the Black Sea

3132-580: Is thought of as starting at the land-atmosphere boundary and so it is important to have adequate knowledge of both precipitation and evaporation. Precipitation can be measured in various ways: disdrometer for precipitation characteristics at a fine time scale; radar for cloud properties, rain rate estimation, hail and snow detection; rain gauge for routine accurate measurements of rain and snowfall; satellite for rainy area identification, rain rate estimation, land-cover/land-use, and soil moisture, snow cover or snow water equivalent for example. Evaporation

3240-477: Is thought the climate conditions established in western Europe mediate the heat and precipitation fluxes reaching Central Europe and Eurasia, regulating the formation of winter cyclones , which are largely responsible for regional precipitation inputs and influence Mediterranean sea surface temperatures (SSTs). The relative strength of these systems also limits the amount of cold air arriving from northern regions during winter. Other influencing factors include

3348-513: Is utilized to formulate operating rules for large dams forming part of systems which include agricultural, industrial and residential demands. Hydrological models are simplified, conceptual representations of a part of the hydrologic cycle. They are primarily used for hydrological prediction and for understanding hydrological processes, within the general field of scientific modeling . Two major types of hydrological models can be distinguished: Recent research in hydrological modeling tries to have

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3456-604: The Aegean Sea . While the net flow of water through the Bosporus and Dardanelles (known collectively as the Turkish Straits ) is out of the Black Sea, water generally flows in both directions simultaneously: Denser, more saline water from the Aegean flows into the Black Sea underneath the less dense, fresher water that flows out of the Black Sea. This creates a significant and permanent layer of deep water that does not drain or mix and

3564-474: The Caspian tiger ( Panthera tigris tigris ) was a resident across the steppes of Ukraine, including Danube Delta, and once, they were hunted to extinction and they're extirpated. The East Asian raccoon dog ( Nyctereutes procyonoides ), bizam/introduced muskrat ( Ondatra zibethica ), and to some extent South American nutria ( Myocastor coypus ), are recent species that have successfully adapted. The firm land of

3672-577: The Danube , Dnieper and Dniester . Consequently, while six countries have a coastline on the sea, its drainage basin includes parts of 24 countries in Europe. The Black Sea, not including the Sea of Azov , covers 436,400 km (168,500 sq mi), has a maximum depth of 2,212 m (7,257 ft), and a volume of 547,000 km (131,000 cu mi). Most of its coasts ascend rapidly. These rises are

3780-618: The Greeks and Romans , while history shows that the Chinese built irrigation and flood control works. The ancient Sinhalese used hydrology to build complex irrigation works in Sri Lanka , also known for the invention of the Valve Pit which allowed construction of large reservoirs, anicuts and canals which still function. Marcus Vitruvius , in the first century BC, described a philosophical theory of

3888-691: The International Court of Justice . Under the presidency of Kuchma , Ukraine had responded that Romania was only afraid of the competition that the new channel would bring, and continued working on the channel. Under the presidency of Yuschenko , who visited Romania in 2005, both sides agree that professionals should decide the fate of the channel. In the long run, Ukraine plans to build a navigation channel, if not through Bistroe Channel, then through another channel. Carpathians ( peaks ) Plains & Delta Islands Rivers ( Danube ) Lakes Black Sea A series of articles on control of

3996-585: The Kartvelian tribe of Speris or Saspers . Other modern names such as Chyornoye more and Karadeniz (both meaning Black Sea) originated during the 13th century. A 1570 map Asiae Nova Descriptio from Abraham Ortelius 's Theatrum Orbis Terrarum labels the sea Mar Maggior (Great Sea), compare Latin Mare major . English writers of the 18th century often used Euxine Sea ( / ˈ j uː k s ɪ n / or / ˈ j uː k ˌ s aɪ n / ). During

4104-637: The Ottoman Empire , it was called either Bahr-e Siyah ( Perso-Arabic ) or Karadeniz ( Ottoman Turkish ), both meaning "Black Sea". The International Hydrographic Organization defines the limits of the Black Sea as follows: On the Southwest. The Northeastern limit of the Sea of Marmara [A line joining Cape Rumili with Cape Anatoli (41°13'N)]. In the Kertch Strait . A line joining Cape Takil and Cape Panaghia (45°02'N). The area surrounding

4212-475: The Pannonian steppe ecosystem of eastern Europe, with Mediterranean influences. As a young region in full process of consolidation, the Danube Delta represents a very favourable place for the development of highly diverse flora and fauna , unique in Europe, with numerous rare species. It hosts 23 natural ecosystems, but due to the extent of wetlands an aquatic environment is prevalent; a terrestrial environment

4320-749: The Pontic Mountains to the south, bar the southwest-facing peninsulas, the Caucasus Mountains to the east, and the Crimean Mountains to the mid-north. In the west, the coast is generally small floodplains below foothills such as the Strandzha ; Cape Emine , a dwindling of the east end of the Balkan Mountains ; and the Dobruja Plateau considerably farther north. The longest east–west extent

4428-399: The return period of such events. Other quantities of interest include the average flow in a river, in a year or by season. These estimates are important for engineers and economists so that proper risk analysis can be performed to influence investment decisions in future infrastructure and to determine the yield reliability characteristics of water supply systems. Statistical information

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4536-660: The 15th century, the Danube Delta became part of the Ottoman Empire . In 1812, following the Russo-Turkish War , the borders of the Ottoman and Russian Empires were set by the Kilia and Old Stambul Channels of the Danube, and in 1829 by the St George Channel. The Treaty of Paris of 1856 , which ended the Crimean War , assigned the Danube Delta to the Ottoman Empire and established an international commission which undertook

4644-455: The 20th century, while governmental agencies began their own hydrological research programs. Of particular importance were Leroy Sherman's unit hydrograph , the infiltration theory of Robert E. Horton , and C.V. Theis' aquifer test/equation describing well hydraulics. Since the 1950s, hydrology has been approached with a more theoretical basis than in the past, facilitated by advances in the physical understanding of hydrological processes and by

4752-628: The Biosphere , the 6,264.03km of the Danube Delta were established as a biosphere reserve , shared by Romania and Ukraine. Historically, in Romania, part of the Danube Delta was marked as a reserve in 1938. In Ukraine, the Danube branch of the Black Sea State Reserve was established in 1973. In 1981, it was reorganized into the Natural Reserve "Danube Fluxes", and in 1998, it was extended into

4860-573: The Black Sea Depression they are terrigenous non-carbonate silts , and at the foot of the continental slope turbidite sediments. The Black Sea is the world's largest body of water with a meromictic basin. The deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is anoxic water. The Black Sea's circulation patterns are primarily controlled by basin topography and fluvial inputs, which result in

4968-526: The Black Sea belong to Bulgaria, Romania, Turkey, and Ukraine: Short-term climatic variation in the Black Sea region is significantly influenced by the operation of the North Atlantic oscillation , the climatic mechanisms resulting from the interaction between the north Atlantic and mid-latitude air masses. While the exact mechanisms causing the North Atlantic Oscillation remain unclear, it

5076-585: The Black Sea features a range of trophic groups, with autotrophic algae, including diatoms and dinoflagellates , acting as primary producers. The fluvial systems draining Eurasia and central Europe introduce large volumes of sediment and dissolved nutrients into the Black Sea, but the distribution of these nutrients is controlled by the degree of physiochemical stratification, which is, in turn, dictated by seasonal physiographic development. During winter, strong wind promotes convective overturning and upwelling of nutrients, while high summer temperatures result in

5184-608: The Black Sea is commonly referred to as the Black Sea Region . Its northern part lies within the Chernozem belt (black soil belt) which goes from eastern Croatia ( Slavonia ), along the Danube (northern Serbia, northern Bulgaria ( Danubian Plain ) and southern Romania ( Wallachian Plain ) to northeast Ukraine and further across the Central Black Earth Region and southern Russia into Siberia . The littoral zone of

5292-806: The Black Sea is often referred to as the Pontic littoral or Pontic zone . The largest bays of the Black Sea are Karkinit Bay in Ukraine; the Gulf of Burgas in Bulgaria; Dnieprovski Bay and Dniestrovski Bay, both in Ukraine; and Sinop Bay and Samsun Bay, both in Turkey. The largest rivers flowing into the Black Sea are: These rivers and their tributaries comprise a 2-million km (0.77-million sq mi) Black Sea drainage basin that covers wholly or partially 24 countries: Unrecognised states: Some islands in

5400-517: The Bosporus Strait from the Mediterranean Sea into the Black Sea, where the water has a lower salt content. Because of the anoxic water at depth, organic matter, including anthropogenic artifacts such as boat hulls, are well preserved. During periods of high surface productivity, short-lived algal blooms form organic rich layers known as sapropels . Scientists have reported an annual phytoplankton bloom that can be seen in many NASA images of

5508-483: The Bosporus is located at 36.5 m (120 ft) below present sea level (deepest spot of the shallowest cross-section in the Bosporus, located in front of Dolmabahçe Palace ) and has a wet section of around 38,000 m (410,000 sq ft). Inflow and outflow current speeds are averaged around 0.3 to 0.4 m/s (1.0 to 1.3 ft/s), but much higher speeds are found locally, inducing significant turbulence and vertical shear. This allows for turbulent mixing of

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5616-402: The Danube Delta a place of emigration, or transit at least. Very few of those born in the region stay there through adulthood; at the same time, the origins of its inhabitants vary widely, as people from many parts of Romania can be found in the delta. The total population has remained more or less constant throughout the 20th century; there were 12,000 inhabitants in the 1890s, and 14,000 before

5724-404: The Danube Delta. Vegetation of this ecosystem consists of the common reed ( Phragmites communis ) and, on near river banks, mace reed/cattail ( Typha latifolia , Typha angustifolia ), sedge ( Carex dioica , Carex stricta ), Dutch rush ( Scirpus radicans , Schoenoplectus lacustris ), and brook mint ( Mentha aquatica ). They provide ideal spawning and nesting grounds. The plaur are

5832-455: The Danube basin during the 1st and 2nd millennium. Geologist Liviu Giosan told The New York Times : Probably 40 percent of the Delta was built in the last 1000 years. Finding that was like a eureka moment. At present, the delta suffers from a large sediment deficit , after the construction of dams on the Danube and its tributaries in the later half of the 20th century. However, construction of

5940-451: The Danube biosphere reserve. Large-scale works began in the Danube Delta as early as the second half of the 19th century. First corrections of the Sulina arm began in 1862, and they continued throughout the 20th century. As a result, the length of the Sulina arm was reduced from 92 to 64 km, and its flow more than doubled, thus making it suitable for large-vessel navigation. Correcting the six large meanders on its course thereby reduced

6048-582: The Danube, in chronological order Black Sea Unrecognised states: The Black Sea is a marginal mediterranean sea lying between Europe and Asia , east of the Balkans , south of the East European Plain , west of the Caucasus , and north of Anatolia . It is bounded by Bulgaria , Georgia , Romania , Russia , Turkey , and Ukraine . The Black Sea is supplied by major rivers, principally

6156-462: The Letea levee, these exotic-looking forests grow especially in the depressions between the sand dunes, in small groves called hasmace . Fauna of this region include the meadow viper ( Vipera ursinii ), osprey ( Pandion haliaetus ), and Eurasian eagle owl ( Bubo bubo ). With an average population density of 2 people per km, the Danube Delta is one of the least inhabited regions of temperate Europe. On

6264-647: The Mid-Black Sea High, which includes the Andrusov Ridge, Tetyaev High, and Archangelsky High, extending south from the Crimean Peninsula . The basin includes two distinct relict back-arc basins which were initiated by the splitting of an Albian volcanic arc and the subduction of both the Paleo - and Neo- Tethys oceans, but the timings of these events remain uncertain. Arc volcanism and extension occurred as

6372-562: The N:P:Si ratio in the basin. Coastal areas, accordingly, have seen an increase in the frequency of monospecific phytoplankton blooms, with diatom-bloom frequency increasing by a factor of 2.5 and non-diatom bloom frequency increasing by a factor of 6. The non-diatoms, such as the prymnesiophytes Emiliania huxleyi (coccolithophore), Chromulina sp., and the Euglenophyte Eutreptia lanowii , can out-compete diatom species because of

6480-777: The Neo-Tethys Ocean subducted under the southern margin of Laurasia during the Mesozoic . Uplift and compressional deformation took place as the Neotethys continued to close. Seismic surveys indicate that rifting began in the Western Black Sea in the Barremian and Aptian followed by the formation of oceanic crust 20 million years later in the Santonian . Since its initiation, compressional tectonic environments led to subsidence in

6588-464: The Rim Current. The Rim Current has a maximum velocity of about 50–100 cm/s (20–39 in/s). Within this feature, two smaller cyclonic gyres operate, occupying the eastern and western sectors of the basin. The Eastern and Western Gyres are well-organized systems in the winter but dissipate into a series of interconnected eddies in the summer and autumn. Mesoscale activity in the peripheral flow becomes more pronounced during these warmer seasons and

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6696-473: The Romanian side live about 20,000 people, of whom 4,600 live in the port of Sulina .. The rest of the population is scattered among 27 villages, of which only three, all situated marginally, had more than 500 people in 2002. The city of Tulcea , at the western edge of the delta, has a population of 92,000 (in 2002); it represents the node of the region and the gate to the delta. Its acute isolation and harsh conditions of living, based mainly on subsistence, made

6804-638: The Second World War. Romanians account for approximately 80% of the population, and Ukrainians for 10%. Other people living in the delta include ethnic minorities such as Greeks, Turks and Bulgarians (in 1992). Distinctive to the region, but very rare as an ethnic entity, are the Lipovans , descendants of the Orthodox Old Rite followers who fled from religious persecution in Russia during the 18th century. On

6912-409: The St. George II (0 BC–present) and the Chilia or Kilia (1600 AD–present). Several other internal lobes were constructed in the lakes and lagoons bordering the Danube Delta to the north (Chilia I and II) and toward the south (Dunavatz). Much of the alluvium in the delta and major expansion of its surface area in the form of lobes resulted from soil erosion associated with human clearing of forests in

7020-406: The Turkish Straits, that the Black Sea joins the World Ocean . During geological periods when this hydrological link was not present, the Black Sea was an endorheic basin , operating independently of the global ocean system (similar to the Caspian Sea today). Currently, the Black Sea water level is relatively high; thus, water is being exchanged with the Mediterranean. The Black Sea undersea river

7128-420: The Ukrainian side, located at the northern edge of the delta, the town of Izmail has a population of 85,000, Kiliya a population of 21,800, and Vilkovo , the main center of the Lipovan community, a population of 9,300. Recorded history notes that the Dacians lived in the Danube Delta before it was conquered by the Romans . After later invasion by the Goths , the region changed hands many times. During

7236-513: The advent of computers and especially geographic information systems (GIS). (See also GIS and hydrology ) The central theme of hydrology is that water circulates throughout the Earth through different pathways and at different rates. The most vivid image of this is in the evaporation of water from the ocean, which forms clouds. These clouds drift over the land and produce rain. The rainwater flows into lakes, rivers, or aquifers. The water in lakes, rivers, and aquifers then either evaporates back to

7344-515: The arms and bigger channels of the Danube. On the levees of Letea and Caraorman , mixed forests of oaks ( Quercus robur , and Quercus pedunculiflora ) with various other trees ( Fraxinus pallisiae , Ulmus foliaceae , Populus tremula ), shrubs ( Prunus spinosa , Crataegus monogyna , Rosa canina , and Berberis vulgaris , among others), and vines ( Vitis sylvestris , Hedera helix , Humulus lupulus , Periploca graeca , which reaches up to 25m) grow on sand dune areas. On

7452-530: The atmosphere or eventually flows back to the ocean, completing a cycle. Water changes its state of being several times throughout this cycle. The areas of research within hydrology concern the movement of water between its various states, or within a given state, or simply quantifying the amounts in these states in a given region. Parts of hydrology concern developing methods for directly measuring these flows or amounts of water, while others concern modeling these processes either for scientific knowledge or for making

7560-425: The basin, interspersed with extensional phases resulting in large-scale volcanism and numerous orogenies , causing the uplift of the Greater Caucasus , Pontides , southern Crimean Peninsula and Balkanides mountain ranges. During the Messinian salinity crisis in the neighboring Mediterranean Sea , water levels fell but without drying up the sea. The collision between the Eurasian and African plates and

7668-470: The breeding pattern of fish has been disrupted, and the flows in the main arms have increased, with serious consequences regarding the discharge of alluvia and the erosion of banks. Reed was intensively harvested during the Communist era. The regime had plans to transform the delta into a large agro-industrial zone. Although the first modern agricultural exploitation dates from 1939 (Ostrovul Tãtaru), only after 1960 were large areas drained and converted, to

7776-519: The centre of the Black Sea reaches a maximum depth of 2,212 metres (7,257.22 feet) just south of Yalta on the Crimean Peninsula . The Paleo- Euxinian is described by the accumulation of eolian silt deposits (related to the Riss glaciation ) and the lowering of sea levels ( MIS 6, 8 and 10). The Karangat marine transgression occurred during the Eemian Interglacial (MIS 5e). This may have been

7884-401: The dark color of the water or climatic conditions. Some scholars understand the name to be derived from a system of colour symbolism representing the cardinal directions , with black or dark for north, red for south, white for west, and green or light blue for east. Hence, "Black Sea" meant "Northern Sea". According to this scheme, the name could only have originated with a people living between

7992-533: The delta during summer, of which 166 are hatching species and 159 are migratory. Over one million individual birds (including swans, ducks, and coots ) winter here. This comprises the arms of the Danube, and a series of its more important streamlets and channels. It is an environment rich in plankton , worms, molluscs , grubs , and sponges , with numerous species of fish, such as the carp , pike , pike perch , sheat-fish , and freshwater sturgeons ( sterlet , Vyza and Danube mackerel). This environment includes

8100-435: The delta used to be covered with large groves of willow trees, which have been cut down almost entirely and replaced with Canadian poplars. On the river banks kept in their natural state, small groves of willow trees ( Salix alba , Salix fragilis , Salix purpurea , Salix pentandra , and Salix triandra ) can still be found, mixed with white poplar ( Populus alba ). Occasionally, the willow trees form corridors along

8208-403: The detriment of the wetlands. In 1991, agricultural land in the delta surpassed 100,000 hectares, and more than a third of its surface has been affected by crop cultivation, forest plantation , or pisciculture (fish farming). As a result of these changes, along with the increasing pollution and eutrophication of the waters of the Danube, and decades of exploitation and poor fishing regulations,

8316-687: The estuary of the Marrassantiya River, the modern Kızıl Irmak , on the Black Sea coast." The principal Greek name Póntos Áxeinos is generally accepted to be a rendering of the Iranian word * axšaina- ("dark colored"). Ancient Greek voyagers adopted the name as Á-xe(i)nos , identified with the Greek word áxeinos (inhospitable). The name Πόντος Ἄξεινος Póntos Áxeinos (Inhospitable Sea), first attested in Pindar ( c.  475 BC ),

8424-563: The fish population has been visibly reduced. In 2004, Ukraine inaugurated work on the Bistroe Channel that would provide an additional navigable link from the Black Sea to the populous Ukrainian section of the Danube Delta. However, because of the negative impact which this new channel might have on the fragile ecosystem of the delta, the European Union advised Ukraine to shut down the works. Romanian officials threatened to sue Ukraine at

8532-464: The fish, the most important are Tench ( Tinca tinca ), common bream ( Abramis brama ), common rudd ( Scardinius erythropthalmus ), Prussian carp ( Carassius auratus gibelio ), wels catfish ( Silurus glanis ), European perch ( Perca fluviatilis ), and northern pike ( Esox lucius ). Reed plants and floating reed islands (called plaur in Romania ) are the most common and well-known components of

8640-685: The future behavior of hydrologic systems (water flow, water quality). One of the major current concerns in hydrologic research is "Prediction in Ungauged Basins" (PUB), i.e. in basins where no or only very few data exist. The aims of Statistical hydrology is to provide appropriate statistical methods for analyzing and modeling various parts of the hydrological cycle. By analyzing the statistical properties of hydrologic records, such as rainfall or river flow, hydrologists can estimate future hydrologic phenomena. When making assessments of how often relatively rare events will occur, analyses are made in terms of

8748-556: The highest sea levels reached in the late Pleistocene . Based on this some scholars have suggested that the Crimean Peninsula was isolated from the mainland by a shallow strait during the Eemian Interglacial. The Neoeuxinian transgression began with an inflow of waters from the Caspian Sea . Neoeuxinian deposits are found in the Black Sea below −20 m (−66 ft) water depth in three layers. The upper layers correspond with

8856-461: The hydrologic cycle, in which precipitation falling in the mountains infiltrated the Earth's surface and led to streams and springs in the lowlands. With the adoption of a more scientific approach, Leonardo da Vinci and Bernard Palissy independently reached an accurate representation of the hydrologic cycle. It was not until the 17th century that hydrologic variables began to be quantified. Pioneers of

8964-430: The important areas of hydrology is the interchange between rivers and aquifers. Groundwater/surface water interactions in streams and aquifers can be complex and the direction of net water flux (into surface water or into the aquifer) may vary spatially along a stream channel and over time at any particular location, depending on the relationship between stream stage and groundwater levels. In some considerations, hydrology

9072-465: The lakes, and various ponds, streamlets and channels. It is characterized by a rich floating and submerse flora ( Myriophyllum , Ceratophyllum , Vallisneria , under the water; Nymphaea alba , Nuphar lutea , Trapa natans , Alisma plantago , floating plants with roots near the lakes' borders; and Salvinia natans , Stratiotes aloides , Spirogyra , floating plants without roots, having negative effect for aquatic bioproductivity ). Of

9180-518: The late 1980s. Additionally, an alien species—the warty comb jelly ( Mnemiopsis leidyi )—established itself in the basin, exploding from a few individuals to an estimated biomass of one billion metric tons. The change in species composition in Black Sea waters also has consequences for hydrochemistry, as calcium-producing coccolithophores influence salinity and pH, although these ramifications have yet to be fully quantified. In central Black Sea waters, silicon levels also reduced significantly, due to

9288-478: The length of the Sfântu Gheorghe branch from 108 to 70km, and its flow also increased somewhat. Both these increases were made to the detriment of the Chilia arm, which at present remains the most unspoiled arm of the main three. These corrections, as well as the digging of various secondary channels throughout the body of the delta, have had a serious impact on the ecosystem. Natural environments have been altered,

9396-407: The limited availability of silicon, a necessary constituent of diatom frustules. As a consequence of these blooms, benthic macrophyte populations were deprived of light, while anoxia caused mass mortality in marine animals. Overfishing during the 1970s further compounded the decline in macrophytes, while the invasive ctenophore Mnemiopsis reduced the biomass of copepods and other zooplankton in

9504-403: The maximum rate at which the soil can absorb water, depends on several factors. The layer that is already saturated provides a resistance that is proportional to its thickness, while that plus the depth of water above the soil provides the driving force ( hydraulic head ). Dry soil can allow rapid infiltration by capillary action ; this force diminishes as the soil becomes wet. Compaction reduces

9612-452: The modern science of hydrology include Pierre Perrault , Edme Mariotte and Edmund Halley . By measuring rainfall, runoff, and drainage area, Perrault showed that rainfall was sufficient to account for the flow of the Seine. Mariotte combined velocity and river cross-section measurements to obtain a discharge value, again in the Seine. Halley showed that the evaporation from the Mediterranean Sea

9720-464: The most extensive strand plains of the delta (Letea and Caraorman strand plains) stand higher (12.4 m and 7 m respectively). The largest lakes are lakes Dranov (21.7km), Roșu (14.5km) and Gorgova (13.8km). The Danube branches into three main distributaries into the delta , Chilia , Sulina , and Sfântul Gheorghe (Saint George) . The last two branches form the Tulcea channel, which continues as

9828-889: The movement, distribution, and management of water on Earth and other planets, including the water cycle , water resources , and drainage basin sustainability. A practitioner of hydrology is called a hydrologist . Hydrologists are scientists studying earth or environmental science , civil or environmental engineering , and physical geography . Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation , natural disasters , and water management . Hydrology subdivides into surface water hydrology, groundwater hydrology ( hydrogeology ), and marine hydrology. Domains of hydrology include hydrometeorology , surface hydrology , hydrogeology , drainage-basin management, and water quality . Oceanography and meteorology are not included because water

9936-431: The north of the basin is up to 190 km (120 mi) wide and features a shallow apron with gradients between 1:40 and 1:1000. The southern edge around Turkey and the eastern edge around Georgia , however, are typified by a narrow shelf that rarely exceeds 20 km (12 mi) in width and a steep apron that is typically 1:40 gradient with numerous submarine canyons and channel extensions. The Euxine abyssal plain in

10044-547: The northern (black) and southern (red) seas : this points to the Achaemenids (550–330 BC). In the Greater Bundahishn , a Middle Persian Zoroastrian scripture, the Black Sea is called Siyābun . In the tenth-century Persian geography book Hudud al-'Alam , the Black Sea is called Georgian Sea ( daryā-yi Gurz ). The Georgian Chronicles use the name zğua sperisa ზღუა სპერისა (Sea of Speri) after

10152-454: The outflow of fresher Black Sea surface-water into the Sea of Marmara occurs near the surface. According to Gregg (2002), the outflow is 16,000 cubic metres per second (570,000 cubic feet per second) or around 500 cubic kilometres per year (120 cubic miles per year), and the inflow is 11,000 m /s (390,000 cu ft/s) or around 350 km /a (84 cu mi/a). The following water budget can be estimated: The southern sill of

10260-501: The peak of the Khvalinian transgression, on the shelf shallow-water sands and coquina mixed with silty sands and brackish-water fauna, and inside the Black Sea Depression hydrotroilite silts. The middle layers on the shelf are sands with brackish-water mollusc shells. Of continental origin, the lower level on the shelf is mostly alluvial sands with pebbles, mixed with less common lacustrine silts and freshwater mollusc shells . Inside

10368-488: The photic zone, enhancing productivity. In total, the Black Sea's biodiversity contains around one-third of the Mediterranean's and is experiencing natural and artificial invasions or "Mediterranizations". The main phytoplankton groups present in the Black Sea are dinoflagellates , diatoms , coccolithophores and cyanobacteria . Generally, the annual cycle of phytoplankton development comprises significant diatom and dinoflagellate-dominated spring production, followed by

10476-461: The porosity and the pore sizes. Surface cover increases capacity by retarding runoff, reducing compaction and other processes. Higher temperatures reduce viscosity , increasing infiltration. Soil moisture can be measured in various ways; by capacitance probe , time domain reflectometer or tensiometer . Other methods include solute sampling and geophysical methods. Hydrology considers quantifying surface water flow and solute transport, although

10584-488: The region. As a result of these characteristics the Black Sea has gained interest from the field of marine archaeology , as ancient shipwrecks in excellent states of preservation have been discovered, such as the Byzantine wreck Sinop D , located in the anoxic layer off the coast of Sinop, Turkey . Modelling shows that, in the event of an asteroid impact on the Black Sea, the release of hydrogen sulfide clouds would pose

10692-457: The regional topography , as depressions and storm systems arriving from the Mediterranean are funneled through the low land around the Bosporus, with the Pontic and Caucasus mountain ranges acting as waveguides, limiting the speed and paths of cyclones passing through the region. The Black Sea is divided into two depositional basins—the Western Black Sea and Eastern Black Sea—separated by

10800-518: The sea was called the "Inhospitable Sea Πόντος Ἄξεινος Póntos Áxeinos by the inhabitants of the Pontus region of the southern shoreline before Greek colonisation due to its difficult navigation and hostile barbarian natives (7.3.6), and that the name was changed to "hospitable" after the Milesians colonised the region, bringing it into the Greek world. Popular supposition derives "Black Sea" from

10908-486: The shortest arm, which consequently led to its extensive use for traffic and severe transformation. At its mouth is located the main port and a single settlement with urban characteristics of the Romanian part of the delta. Because of the alluvium deposited at its mouth, a channel gradually advancing into the sea (presently it has 10km) was built in order to protect navigation. Sfântul Gheorghe ( Saint George in English), in

11016-582: The south, is the oldest and most sparsely populated. Its alluvium has led to the creation, beginning in 1897, of the Sacalin Islands , which today measures 19km in length. The Danube Delta is considred to be among Romania's sunniest and driest regions. The mean annual temperature is 11°C (−1°C in January and 22 °C in July), with mean precipitation between 400mm/year and 300mm/year. The Danube Delta falls within

11124-440: The treatment of flows in large rivers is sometimes considered as a distinct topic of hydraulics or hydrodynamics. Surface water flow can include flow both in recognizable river channels and otherwise. Methods for measuring flow once the water has reached a river include the stream gauge (see: discharge ), and tracer techniques. Other topics include chemical transport as part of surface water, sediment transport and erosion. One of

11232-408: The two layers. Surface water leaves the Black Sea with a salinity of 17 practical salinity units (PSU) and reaches the Mediterranean with a salinity of 34 PSU. Likewise, an inflow of the Mediterranean with salinity 38.5 PSU experiences a decrease to about 34 PSU. Mean surface circulation is cyclonic ; waters around the perimeter of the Black Sea circulate in a basin-wide shelfbreak gyre known as

11340-604: The variables constituting the terrestrial water balance, for example surface water storage, soil moisture , precipitation , evapotranspiration , and snow and ice , are measurable using remote sensing at various spatial-temporal resolutions and accuracies. Sources of remote sensing include land-based sensors, airborne sensors and satellite sensors which can capture microwave , thermal and near-infrared data or use lidar , for example. In hydrology, studies of water quality concern organic and inorganic compounds, and both dissolved and sediment material. In addition, water quality

11448-582: The westward escape of the Anatolian block along the North Anatolian and East Anatolian faults dictates the current tectonic regime, which features enhanced subsidence in the Black Sea basin and significant volcanic activity in the Anatolian region. These geological mechanisms, in the long term, have caused the periodic isolations of the Black Sea from the rest of the global ocean system. The large shelf to

11556-506: Was considered an ill omen and was euphemized to its opposite, Εὔξεινος Πόντος Eúxeinos Póntos (Hospitable Sea), also first attested in Pindar. This became the commonly used designation in Greek, although in mythological contexts the "true" name Póntos Áxeinos remained favoured. Strabo 's Geographica (1.2.10) reports that in antiquity, the Black Sea was often simply called "the Sea" ( ὁ πόντος ho Pontos ). He thought that

11664-603: Was sufficient to account for the outflow of rivers flowing into the sea. Advances in the 18th century included the Bernoulli piezometer and Bernoulli's equation , by Daniel Bernoulli , and the Pitot tube , by Henri Pitot . The 19th century saw development in groundwater hydrology, including Darcy's law , the Dupuit-Thiem well formula, and Hagen- Poiseuille 's capillary flow equation. Rational analyses began to replace empiricism in

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