Danube water

At present, the average shares of the river water input to the Chilia, Tulcea, Sulina, and Gheorghe branches are approximately equal to 52, 48, 21 and 27%, respectively. The tendency in redistribution of the Danube water runoff in favor of the Tulcea and Gheorghe branches is retained. 

During the second part of the 20th century, river flux of organic matter, nutrients and pollutants markedly increased. For example, increase in concentration of ammonia nitrogen is 2.5 times, of nitrites and nitrates 4 and 5 times respectively, of phosphate 2 times. Since the beginning of 1970s, the concentration of heavy metals and oil in river water has also increased [9]. Over the period 1996-2000, the input of the contaminants to the Black Sea with the Danube waters comprises oil 53 x 1012 t, Cu 1.2 x 1012 t, and Zn 3.3 x 1012t [9],... 

The mixing zone of river fresh water with salinity less than 0.5%o and sea brackish water with salinity up to 18%> occupies a bend up to 20-30 km in width during high-flow period and western winds and of 3-5 km during the low-flow period and eastern winds [7,30]. The Danube water spreads mainly on the surface with layer from 1-3 to 5 m [9]. The Danube River water runoff and its distribution between delta branches play a very important role not only in hydrological and hydrochemical regime of the delta and mouth nearshore zone but also in formation of ecological conditions in the northwestern part of the Black Sea as a whole [7,9,30]. 

Observations show that the area of hypoxia directly depends on volume of the Danube water runoff during spring-summer flood. Besides, this area depends on the time of the flood peak [9,31]. If the flood peak takes place in April, the river fresh waters are driven out of the northwestern part of the Black Sea in the south direction under the influence of predominated northern winds in this time, and hypoxia is absent. Other situation takes place if the flood peak falls on May or June, when under the impact of the southern winds, main mass of river fresh water remains in the northwestern part of the Black Sea. In this case, hypoxia forms later and in the area between the Danube and Dniester mouths [9,31]. 

The present state of the Danube water quality, characterized by classical quality parameters, is generally acceptable but with a slow degradation trend. The levels of organochlorinated insecticides in drinking water of the main riverside localities are shown in Figures 23.4 and 23.S (gas chromatography with electron capture detection was used as the analytical technique). 

During 1986/1987, complex limnological studies were performed in the Yugoslav part of the Danube. The aim of these investigations was to establish the Danube water quality and the degree of eutrophication. One of the sampling spots was at Novi Sad [17]. 

Testing indicated that the Danube water in the Pancevo zone contained a high concentration of total hydrocarbons, particularly in layers above the bottom where it... 

Water samples from the canal contained leaked DCE (28.6 and 42.3 (tg L" ) but it was not found in the Danube water samples from the downstream profile. 

Analyses of the relations among the benthic fauna communities upstream from the canal in terms of saprobity put the Danube water in the class of moderately polluted. The composition and structure of benthic communities and sapiobiologi-cal analyses at the Banatska Palanka - Ram profile indicated the presence of organic pollution. The saprobity index S varied from 2.93 to 3.23. 

From the results of our testing it is clear that both toxic and genotoxic effects of the Danube water result from the water coming from the canal even 5 months after the chemicals leaked into the canal. The absence of these effects in upstream sample proves this. The positive results obtained in the test should be considered as a warning of risk to both human health and water environment [48]. 

Kalafatic V, Martinovic- 6tanovic V, Tanaskovic M (1989) Evaluation of the Danube water quality near Vinca village from water supply aspect. International conference on water pollution control in the basin of the River Danube, Preconference proceedings, Novi Sad, pp 346-350... 

Sackmauerova, M., O. Pal usova, and A. Szokolay. 1977. Contribution to the study of drinking water, Danube water and biocenose contamination with chlorinated insecticides. Water Research 11 551-556. 

Veningerova M, Prachar V, Kovacicova J, et al. 1998. Levels of chlorinated phenols in Danube river water. Fresenius Environ Bull 7 224-231. 

Balinova AM, Mondesky M. 1999. Pesticide contamination ground and surface water in Bulgarian Danube Plain. J Environ Sci Health B 34(l) 33-46. 

The third period (1986-1994) was marked by a return to the range of 9-13.5%, similar to that in the first period but with a higher interannual variation (coefficient of variation 14.7%). Unlike the situation in the second period, the early years of the third showed a negative correlation between fatness and stock density. It is worth mentioning that sprat from around the island of Zmeiny were almost always fatter than their counterparts in waters around the Cape of Tarkhankut, presumably because of the input of nutrients from the Danube. 

The bulk of the riverine runoff (up to 80%) is delivered to the northwestern part of the sea by the major rivers such as the Danube (200 km3/year), the Dnieper (50 km3/year), and the Dniester (10 km3/year). On the Caucasian coast of the Black Sea, the sea accepts the waters of the Inguri, Rioni, Chorokh, and numerous minor rivers. Over the rest of the coast, the runoff is insignificant. 

During the last 60-100 years [5,21,22], the majority of rivers under consideration were subject to the human-induced decrease in the water runoff and sediment load. The decrease in the water runoff was mainly due to the water withdrawal for economical needs and losses through evaporation from the free-water surface of reservoirs. At the Danube River mouth, however, the climate-induced increase in the water runoff over the recent 30 years has exceeded the human-induced decrease in it. Human-induced decrease of water runoff among large rivers was the greatest in the Dnieper, Don and Kuban rivers and comprised 1.2-1.3 times. 

Due to accumulation of sediments in reservoirs, the sediment load of the majority of rivers decreased much more than their water runoff. A maximum decrease in sediment load has occurred in the Kuban, Don, Rioni, and Danube rivers (by a factor of 5.6,2.8, 2.4 and 1.5, respectively). 

Drastic changes in river water and sediment distribution between delta branches in the Danube and Rioni deltas took place after the artificial canalization, deepening and straightening of some channels. 

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