Diurnal variations of summer phytoplankton and interactions with some physicochemical characteristics under eutrophication in the Dardanelles

Abstract

This study was carried out to determine the diurnal distributions of phytoplankton density, bio-volume, and chlorophyll a in relation to nutrients and CTD measurements in surface waters of the coastal area in the Dardanelles during high density of phytoplankton, especially high diatom production (between 3 July and 4 August 2002). Ninety nine surface samples were collected for nutrient, chlorophyll a, and phytoplankton in 3 different time periods of the day (08:00, 13:00 and 18:00 hours) in the sampling period. Based on the sample analyses, average temperature, salinity, pH, DO, TDS, TSS, NO-2+NO-3, PO-34, SiO4, chlorophyll a, N:P, and Si:P were calculated as 25 °C, 23.3 ppt, 8.42, 9.26 mg L-1, 23.9 g L-1, 36.1 mg L-1, 1.90 μM, 0.24 μM, 3.61 μM, 1.70 μg L-1, 12.5, and 25, respectively. Total phytoplankton density and bio-volume varied from 2.86 × 105 to 1.5 × 107 cells L-1 and from 5.98 × 108 to 8.81 x 1010 μm3 L-1, respectively. Contribution rate of Bacillariophyceae (66.5%) to total phytoplankton bio-volume was higher than that of Dinophyceae (31.0%). Phytoplankton community structure was observed to be controlled by 6-7 species. Other species can be considered as insignificant species that do not cause important fluctuations in the phytoplankton density and bio-volume. It has been reported that there were 9-11 population growth slopes for different species at different times and densities. Therefore, life cycles of phytoplankton species were completed between 3 and 4 days. Diurnal variations of biological and physicochemical parameters in the time interval between 0800 and 18:00 were generally much higher than daily variations between 3 July and 4 August 2002 due to the 2 counter flows system of the Dardanelles and domestic inputs of ^anakkale city. © TÜBİTAK.