Evaluation of seasonal physicochemical conditions and chlorophyll-a concentrations in Izmit Bay, Marmara Sea
Halim Aytekin Ergül
Department of Biology, Faculty of Science and Literature, Kocaeli University, 41380 Kocaeli, TURKEY
Vertical and horizontal gradient of temperature, salinity, density, chlorophyll-a, dissolved oxygen and pH were monitored seasonally between summer 2008 and spring 2010 in the eastern, central and western basins of Izmit Bay (Marmara Sea). Surface seawater temperature ranged from 7.5 to 26 °C during the study period. Thermal stratification was found to be significant in winter and summer. Surface water salinity ranged from 20.9 to 24.0 ‰ in summer 2008 and 2009 and reached up to 36.1 ‰ below halocline layer. Permanent pycnocline and a two-layered stratification were observed throughout the study. Sigma-t seasonally varied between 13.5 and 18.4 in the upper layer and increased up to 27.2 by increasing depth below the intermediate layer. Average seasonal Chl-a concentrations ranged from 1.5 in summer 2008 to 9.6 μg L-1 in spring 2010. The highest average Chl-a concentrations was found in the eastern basin during the study, whereas the maximum Chl-a level was measured as 18 μg L-1 in the central basin in spring 2010. Higher DO concentrations were measured in the western basin while the lowest (i.e., 0.2 mg L-1) was measured in the eastern basin located near the densely populated city center of the Kocaeli Province. Hypoxic conditions occurred in the intermediate layer in summer seasons while it was routinely present in the lower layer. Meteorological conditions impact the oceanography of the bay. In summer 2009, warm air temperature, weak wind speed, accordingly weak vertical water mixing accompanied with warm surface water resulted near surface hypoxia (i.e., below 4 m from the surface) in the eastern basin of Izmit Bay.
Keywords: Izmit Bay, Marmara Sea, chlorophyll-a, hypoxia, wind speed