부산대학교 도서관

Nitrogen transformations were investigated in the Bay of Villefranche-sur-Mer, on the south coast of France, during autumn 1990 and spring 1991, using 15N-isotope techniques on sizefractionated sea water samples. Besides measuring uptake of ammonium and nitrate, and ammonium regeneration, the biological composition in 4 size fractions (< 1 μm, < 10 μm, < 100 μm, and unfractionated water) was determined. The plankton was dominated by pico- and nanoplankton, of which the cyanobacteria and nanoflagellates dominated the autotrophs. Heterotrophic bacteria constituted 70 and 30 % of the < 1 μm and < 10 μm fractions, respectively. During spring, ammonium uptake rates were low and nitrate uptake rates often negligible, resulting in a total dominance (98 to 100%) of regenerated production. In autumn, however, nitrate uptake rates were higher, with new production amounting to 34%. The regenerated production was mostly accomplished by pico- and nanoplankton, especially cyanobacteria and autotrophic nanoflagellates, but also heterotrophic bacteria. When present, the ciliates accounted for the major part of ammonium regeneration, otherwise it was heterotrophic pico- and nanoflagellates. Considering the nitrogen dynamics and the plankton composition, these waters may be considered as mesotrophic.