Caspian Sea 2011
State of the Environment of the Caspian Sea
5. State: Changes in environmental quality (natural capital) 5.1. State of marine water quality and incoming fresh water The Caspian Sea is landlocked with limited flow through. Potential contaminants enter the water body via rivers and are generally retained in the system. There are almost 130 rivers discharging into the Caspian Sea, but the majority has low dis- charge rates (only eight have a developed delta, the Volga, Terek, Sulak, Samur, Kura, Ural, Atrek, and Sefidrud rivers). The largest inflow of freshwa- ter comes from the Volga, which accounts for near- ly 80% of the mean river discharge per year (Ko- sarev & Yablonskaya, 1994). The river catchment is extremely large, with an area of approximately 3.5 million km2, of which the Volga catchment ac- counts for 1.4 million km2 (Kosarev, 2005). The northern part of the sea is relatively flat, with a maximum depth of about 10 m. In contrast the southern region, which is part of an active tectonic zone, reaches a maximum depth of 1 025 m. The sea straddles several climatic zones – the north, including the Volga catchment is in the continen- tal climate zone, the west and south are in the warm continental belt, while the east is a desert climate. Generally the shallow northern third of the sea freezes in winter. Sea level is cyclical, gen- erally reaching its lowest value in winter and ris- ing during May–July, following the spring floods (e.g., Domroes et al., 1998). The inflow of fresh- water (compensated by evaporation over the sea), results in the formation of a north - south salin- ity gradient. Surface water’s salinity in the shallow norther region’s ranges from 1-2 ppt in the Volga river mouth to 9-12 ppt in the zone of mixing be- tween the riverine and marine waters. In the south, salinity ranges from 11.5-13.5 ppt (Kosarev, 2005; Tuzhilkin & Kosarev, 2005). Average ocean salinity is 35 ppt). Because of the limited inflow of fresh- water in the southern part of the sea, the seasonal salinity variation is minimal.
Previous studies have shown that industrial discharges into the rivers entering the Caspian Sea contain a wide range of pollutants including petroleum, sulfate, phenol, synthetic surfactants and heavy metals. Agriculture waste is also known to contribute to a reduction in water quality, with large volumes of organic material discharged into the rivers entering the Caspian Sea. The environ- mental impacts of the petroleum industry on the Caspian environment include on-going leakages from inundated historic wells as well as acciden- tal spillages (CEP 2007a). In addition, since the 1990’s, increases in high-tonnage shipping and the creation of port facilities may have added to the pollution load of rivers (Shaw et al., 1998). Because of the closed nature of the Caspian Sea, quantifying river influxes of key variables is important in understanding and managing the environment. The pollutants that enter the sea principally through the Volga, Kura, Terek, and Ural rivers, from industrial sources and munici- pal wastewaters, are transported throughout the sea. A large percentage of the toxic substances, including persistent organic pollutants, have been shown to accumulate in bottom sediments (TACIS 2009b). Revised Transboundary Diagnos- tic Analyses reported that the flux of some pol- lutants entering the Caspian Sea may have di- minished since the 1990s. However, there is little empirical evidence for this, but possible reasons for decline may be a reduction in agricultural and/or industrial activities, improved trapping of contaminants in the reservoirs, especially in the Volga and Kura River basins. Even if there are numbers of national and re- gional efforts to monitor marine and incoming fresh water quality, there are very limited infor- mation available and considerable gaps to build a reasonable assessment over the time. The main reasons of the gaps are insufficient moni- toring system, luck of monitoring programs, and insufficient funds to maintain the operations. Considering these obstacles, analyses of marine and fresh water quality is based on conclusions of the existing and available documents such
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