PARENT SESSION
Symposium 3: Linking ecological processes and environmental impacts across scales: Coastal ecology and energy development in the Caspian Sea and Gulf of Mexico
Organized by: S Tartowski, T Butler, and V Bashkin
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 517 C, Level 5, Palais des congrès de Montréal
River deltas of the Caspian Sea: Fate of pollutants in the changing environment.
Yergaliyev, Tlepkazy*,1, Lychagin, Michail2, 1 Oil and Gas Institute, Atyrau, Kazakhstan2 Faculty of Geography, Moscow, Russia
ABSTRACT- Content of chemical elements and compounds in deltaic sediments is determined by geochemical characteristics of upstream source areas, features of substance transportation in dissolved and suspended forms, sediment lithology, pH and red-ox conditions, and type of sediment pollution. Heavy metals (HM) concentrations and fluxes in river deltas of the Caspian Sea are controlled by both the natural geochemical features of the river basins and the pollution inputs from industrial, municipal and agricultural activity. HM levels were lowest in sediments of the Volga delta. Terek delta sediments had higher values of Zn, Cu and Pb. The Ural delta is enriched with Cr. Bottom sediments of the Kura river are characterized by the highest values of Cu, Ni, Co and Cr. Sediments in the Sefidrud delta, as well as in mouths of smaller rivers of the Iranian coast, show intermediate HM levels. Disparities between the geochemistry of the soils in the river basins and the river delta sediments indicates inputs from pollution sources. HM levels in river sediments of the Volga delta are similar to the composition in basin soils. Sediments of the Kura delta, and especially the Terek delta contain significantly more HM than corresponding soils in the river basins. In the Volga and Kura rivers the flood control structures determine the upstream storage of heavy metals and other pollutants. The absence of large water reservoirs in the Terek basin has allowed the transfer of a greater proportion of HMs to the delta and thus increased the direct impact of industrial activity on the river delta and the Caspian Sea. Changes in river inputs to the Caspian Sea have feedback effects on the geochemistry of the river deltas as well. During 1978-1996 the Caspian Sea level has risen from -29.0 to -26.5 m, recently remaining at about -27.0 m. The sea-level rise caused tremendous changes in geochemical conditions of the Volga avandelta (near shore area), which resulted in the re-distribution of chemical elements. The fresh/brackish water-mixing zone has moved to the north about 20-30 km. Increasing influence of marine water coupled with a large amount of drowned organic matter leads to the sulfidization and a sharp decrease of Eh values in sediments. Formation of the sulfide geochemical barrier has resulted in the recent accumulation of heavy metals, especially Mo and Cd.
Key words: caspian, geochemistry, delta, volga