Size-fractionated phytoplankton and nutrient dynamics in the inner part of İzmir Bay, eastern Aegean Sea

İzmir Bay has been one of most polluted bays of the Mediterranean for a long time. When the “Big Channel Project” was completed in 2000, sewage flow into the bay ended. Hence, the influence of creeks, which are the only source of water transportation to the inner bay, was investigated in the current study. Monthly samples of creek water and seawater were taken. Basic water quality variables and nutrients were measured. In addition, the phytoplankton community was arrayed into size fractions to assess the contribution of each size fraction to biomass and pigment concentrations. Analyses showed that the creek waters had very high nutrient concentrations. Although decreasing nutrient concentrations of the sea as compared to past years were detected, results of the analyses showed that the phytoplankton biomass was increased. Minimum and maximum values of nutrient concentrations and chlorophyll-a were 0.23–22.28 μM for ammonium, 1.54–11.77 μM for nitrate, 0.00–3.51 μM for nitrite, 1.99–41.94 μM for silicate, 0.00–5.96 μM for phosphate, and 5.03–30.26 μg/L for chlorophyll-a. Nanoplankton was the dominant phytoplankton group in the inner bay. An increment in picoplankton was detected towards the outer part of the bay. The microplankton biomass was correlated with NH+ 4-N, [Si(OH)4-Si], and o.PO4-P. [Si(OH)4-Si], o.PO4-P, and microplankton were the most important constituents in the inner bay. Consequently, controlling nutrient concentrations in the creeks might contribute to the cleaning process in İzmir Bay.İzmir Bay has been one of most polluted bays of the Mediterranean for a long time. When the “Big Channel Project” was completed in 2000, sewage flow into the bay ended. Hence, the influence of creeks, which are the only source of water transportation to the inner bay, was investigated in the current study. Monthly samples of creek water and seawater were taken. Basic water quality variables and nutrients were measured. In addition, the phytoplankton community was arrayed into size fractions to assess the contribution of each size fraction to biomass and pigment concentrations. Analyses showed that the creek waters had very high nutrient concentrations. Although decreasing nutrient concentrations of the sea as compared to past years were detected, results of the analyses showed that the phytoplankton biomass was increased. Minimum and maximum values of nutrient concentrations and chlorophyll-a were 0.23–22.28 μM for ammonium, 1.54–11.77 μM for nitrate, 0.00–3.51 μM for nitrite, 1.99–41.94 μM for silicate, 0.00–5.96 μM for phosphate, and 5.03–30.26 μg/L for chlorophyll-a. Nanoplankton was the dominant phytoplankton group in the inner bay. An increment in picoplankton was detected towards the outer part of the bay. The microplankton biomass was correlated with NH+ 4-N, [Si(OH)4-Si], and o.PO4-P. [Si(OH)4-Si], o.PO4-P, and microplankton were the most important constituents in the inner bay. Consequently, controlling nutrient concentrations in the creeks might contribute to the cleaning process in İzmir Bay