New Production and Nitrogen Cycling in the Off-Shore Regions of the Black Sea

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Many scientific papers have been written that detail environmental changes in the Black Sea, and many speculate regarding implications of further potential anthropogenic changes 1) in various drainage basins that provide freshwater to this sea, 2) along its coastal margins, and 3) in extraction of its resources. While the ecological effects of industrial activity and changing land and water use are most apparent in coastal regions of the Black Sea, they are also evident off shore. For example, the observed trend of increasing nutrient concentrations and doublings of both phytoplankton biomass and primary productivity throughout the central region of the sea between the mid 1970s and early 1990s, have been attributed to anthropogenic causes. Perhaps the most dramatic basin wide changes have, however, resulted from accidental introductions of carnivorous gelatinous zooplankton, most recently Mnemiopsis leydii. These species have profoundly affected Black Sea community structure, and probably community dynamics with respect to element and energy flow. There have been no studies of the annual nitrogen cycle and no determinations of new production in the Black Sea. Moreover, generalizations that have been made, such as in models, are predicated upon the generalized behavior of a Black Sea planktonic ecosystem prior to the environmental changes of the last decade. In conjunction with colleagues in Turkey, the off shore nitrogen cycle during all four seasons will be thoroughly investigated. Rates of nitrogen uptake, nitrogen fixation, and nitrogen flux among dissolved components will be measured with stable isotope techniques and interpreted within the context of plankton community structure and hydrography. This study will serve to document current conditions, provide a basis for inferring the effects of recent environmental changes, and contribute to more realistic modeling efforts of the Black Sea ecosystem. In the course of this work our Turkish colleagues will gain experience in the design, analysis and interpretation of results of nitrogen flux experiments, and our facilities will be available to them for follow on studies of changing conditions in the Black Sea. The physical scale of the Black Sea makes a comprehensive study of its pelagic ecosystem tractable. In this regard the Black Sea is an important resource for developing and testing understanding of ecosystem function and stability in more broadly applied coupled physical and biogeochemical models of the pelagic plankton realm.