Temporal variations of surface phytoplankton, nutrients and chlorophyll a in the Dardanelles (Turkish Straits System): a coastal station sample in weekly time intervals

Authors: MUHAMMET TÜRKOĞLU

Abstract: In this study, weekly distributions of inorganic nutrients and phytoplankton cell volumes were investigated in relation to the hydrology of the Dardanelles. The data were collected between March 2001 and March 2002. NO^{-}_{2}+NO^{-}_{3}, PO_{4}^{-3}, and SiO_4 concentrations ranged between 0.050-6.887 µM, 0.051-1.152 µM, and 0.64-10.74 µM, respectively. During the study, the highest nutrient values were measured between late fall and mid-winter. Inorganic N:P and Si:P ratios in the surface water were lower due to high PO_{4}^{-3} concentrations. The chlorophyll a concentrations ranged from 0.03 to 8.67 µg L^{-1}. Phytoplankton cell density and cell volume ranged from 1.54E + 05 to 6.46E + 07 cell L^{-1} (mean 7.65E + 06; SD 1.44E + 07 cell L^{-1}) and from 2.51E + 09 to 8.66E + 10 µm^{-3} L^{-1} (mean 1.98E + 10; SD 1.86E + 10 µm^{-3} L^{-1}) between less productive and high productive periods. During the study period, 8-10 species controlled the phytoplankton community structure in the coastal zone of the Dardanelles. Others did not contribute to the phytoplankton population and they only can be considered as accessory species, which do not cause significant fluctuations in the phytoplankton production. Relationships between chlorophyll a, cell density, and cell volume of phytoplankton revealed that chlorophyll a is rather controlled by the cell density than by the cell volume. Furthermore, the physicochemical variables, such as nutrients and chlorophyll a and phytoplankton cell density and cell volume, are affected by the counter flows in the Dardanelles. Phytoplankton population was more limited by nitrogen than by phosphate due to extra phosphate inputs coming from various sources, such as domestic waste waters as well as the vertical mixing between upper and lower layers.

Keywords: Turkish Straits System, Dardanelles, phytoplankton, chlorophyll a, nutrients

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