Coastal nutrient and pollutant dynamics: The interaction of fast and slow processes.
Tartowski, Sandy1, Bashkin, Vladimir2, 1 Cornell University, Ithaca, USA2 Moscow State University, Moscow, Russia
ABSTRACT- The North basin of the Caspian Sea is cleaner now than in the 1980s and early 1990s and cleaner than widely assumed. Agricultural inputs of nutrients declined with the break-up of the USSR. The Volga River is the main source (more than 80%) of both nutrients and pollutants to the North Caspian. Nutrient fluxes to the North Caspian through the Volga are controlled by upstream dams and other river control structures and by the the downstream processes in the large Volga Delta. The residence time of water in the North Basin is about 1-3 years. The Volga river inputs control the salinity of the North basin which ranges from 0 ppt at the river mouths to approximately 12 ppt at the boundary with the mid Caspian. The North Caspian is highly productive, and production is usually P-limited, but occasionally co-limited by N and P. Nitrogen inputs average 800,000 tons/year, but export to the mid caspian is about 600,000 tons/year. Phytoplankton primary production contributes more than 50% of the organic carbon to the ecosystem (14-22 TG C /yr.), with the remainder flowing into the basin through the Volga and Ural rivers. The annual high flow of the Volga River is usually in late spring, somewhat delayed and decreased by regulation for flood control and human use. The extent of seasonal ice cover is weather dependent, but ice covers most of the North Basin in cooler years. Retreat of the ice is accompanied by an early spring phytoplankton bloom which is sustained by the spring flush from the Volga. The shallow well -mixed basin seldom develops hypoxia or undesirable alga blooms under the current conditions, but has shown signs of eutrophication in the past and is vulnerable to increasing inputs of nutrients which may accompany economic development.
Key words: caspian, nutrient, nitrogen, primary production
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