Assessing the impact of nutrient loads on eutrophication in the semi-enclosed Izmir Bay combining observations and coupled hydrodynamic-ecosystem modelling

Intense human activities may strongly affect coastal environments threatening natural, societal and economic resources. In order to propose adequate measures to preserve coastal marine areas, a thorough understanding of their physical and biogeochemical features is required. This study focuses on one such coastal area, Izmir Bay located in the Eastern Mediterranean Sea. Izmir Bay is a highly populated area subject to many human induced stressors such as pollution and eutrophication, that has been suffering high nutrient loads for decades. Despite the construction of the Çiğli waste water treatment plant in 2000-2001 to reduce eutrophication, such pressures continue to occur. To study the current physical and biogeochemical dynamics of Izmir Bay and their spatial and temporal variability, a three-dimensional coupled hydrodynamic-ecosystem model (Delft3D modelling suite’s FLOW and ECO modules) is implemented. Using the model, the effect of excessive inorganic nutrient loading on the marine ecosystem as the main cause of this eutrophication is explored in an effort to advise on mitigation efforts for the Bay focusing on eliminating eutrophication. Results of different model scenarios show that the Inner and Middle Bay are nitrogen-limited while the Outer Bay is phosphorus-limited. Inner regions are more sensitive to variations in inorganic nitrogen input due to the low (<16) N/P ratio of nutrients in seawater. An increase in inorganic nitrogen triggers eutrophication events with primary production as an immediate response. Conversely, the Outer Bay ecosystem with N/P ratios above 16 is more sensitive to phosphate inputs, of which an increase causes a considerable enhancement in algal production. This study shows the vulnerability of Izmir Bay to anthropogenic nutrient input and model simulations indicate that management plans should consider reducing DIN discharges both in the inner-middle zones of Izmir Bay as well as inputs from the Gediz River. Additionally, phosphate inputs should be reduced to avoid an overall increase of algal production in the Outer Bay, the larger part of Izmir Bay.

Optical characterization of chromophoric dissolved organic matter at eutrophic and oligotrophic parts of a semi-enclosed bay (İzmir, Aegean Sea)

Optical characterization of chromophoric dissolved organic matter (CDOM) from İzmir Bay (Aegean Sea) waters was investigated. For sampling, surface and subsurface seawater from 7 stations were collected in summer 2015. Excitation-emission matrix (EEM) spectra of each sample were recorded on a fluorescence spectrophotometer. The results showed that dissolved organic carbon (DOC) concentrations and EEM peaks were increased from the outer bay to inner bay stations. EEM peaks indicated the presence of both humic-like and protein-like components which were higher at middle-inner bays than outer bay. Spearman’s rank correlation coefficients for EEM peak intensities and DOC concentrations were highly positive (p<0.05). HIX found between 0.73-3.51, whereas BIX ranged from 0.31 to 0.96 in the bay. Humification degree of CDOM in the middle-inner bays were higher compared to outer bay stations. High HIX values in the middle-inner bays could be linked to the presence of Melez stream (heavily polluted), other streams, rain run-offs and maritime activities at İzmir Bay. High BIX values in the middle-inner bays indicated presence of freshly produced DOM from bacterial origin. Optical characterization of CDOM could be used for tracing fluorescent DOM components and determining different DOM sources (autochthonous or allochthonous) in further studies.

Micronucleus formation in mussel’ (Mytilus galloprovincialis, Lamarck 1819) haemolymph, liver, and gill cells as a biomarker in the assessment of genotoxicity in İzmir Bay (Aegean Sea, Turkey)

The sea has involved a large variety of environmental contaminants and plays a crucial role in aquatic ecosystems. The Izmir Bay, which has been rapidly polluted since the 1960s, was one of the intensely polluted areas in the Mediterranean. Organic materials, hydrocarbons, metals, and pathogenic organisms that are accumulated in the region, caused high pollution and threaten health and aesthetics. Because of this, the aim of this paper was focus on to investigations of the genetic damages in mussels in Izmir Bay. Investigations of mutagenic/carcinogenic potential have an advantage in genotoxicity studies because biomarker for pollution exposure in mussel is the early detection of possible long-term effects such as cancer. Therefore, genotoxicity was the focus of the biomarker investigations in mussel during the investigations. Thus, micronucleus tests were afforded to determine genetic damage in the haemolymph, liver, and gills of Mytilus galloprovincialis living in Izmir Bay (Western Coast of Turkey). In the present study, results showed that the frequency of MN was found at a high level in station 4 and station 5 where wastes from dockyard existed contributed to the high level of pollution. The recommendation is to standardize procedures for assessment of the toxic impact of pollutants at the cellular level in aquatic species by using micronucleus assays for biomonitoring of environmental pollution.

Reproductive biology of the rayed pearl oyster (Pinctada imbricata radiata, Leach 1814) in Izmir Bay

The present study was carried out to determine gonadal stages and quality of pearl oyster meat (Pinctada imbricata radiata, Leach, 1814) in Izmir Bay (Turkey). Pearl oyster samples were collected from the study area at a depth of ~5 m between February 2013 and January 2014. The highest and lowest temperature was measured in July and January as 27°C and 14.2°C, respectively. The maximum chlorophyll a value of 4.640 μg l−1 was calculated in May and the lowest value of 1.009 μg l−1 was recorded in April. Individuals reached their first maturity in April. Spawning activity was observed from June to September and the gonad index (GI) was at the highest level during those months. The development was observed from April to February. The overall female to male ratio was 1.32:1 (p < 0.05) and it did not affect the GI (p > 0.05). There is a strong positive correlation between the GI and temperature (p < 0.05). The highest condition index (CI) was recorded in May as 12.31 ± 0.51, whereas the lowest one in January as 7.37 ± 0.22. As a result, this study revealed that the pearl oyster population in the region is characterized by high reproductive activity, especially during the summer months.