Assessment of the trophic status of the Mersin bay waters, Northeastern Mediterranean
Kaptan, Mehmet Salih
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Identifying the spatial and temporal variability of eutrophication related indicators such as Chlorophyll-a (Chl-a), oxygen saturation (DO%), dissolved inorganic nitrogen (DIN) and total phosphorus (TP), as a measure of the potential pressures and productivity, were measured within the Mersin Bay, a wide shelf region of the Cilician Basin located in the Northeastern Mediterranean Sea. This study aims to characterize the trophic status of the water masses in the eastern shelf waters of the bay fed by river discharges, through applying cluster analysis, TRIX (using DIN, TP, DO%, Chl-a) and UNTRIX index approaches, based on data collected seasonally in the eastern bay waters between September 2008 and February 2011. Macro-nutrient (DIN, TP, Si) and Chl-a concentrations were found to be 10-fold high in the polluted shallow nearshore waters (<20 m in depth) compared to the offshore (>50 m) surface values. Cluster analysis of all the data highlighted the presence of three different trophic (eutrophic, mesotrophic and oligotrophic) region characteristics. The nearshore zone was assigned as “Eutrophic” whilst the offshore waters displayed “Oligotrophic” properties. Comparison of the TRIX, TRIX-IMS (modified TRIX with site-specific ‘a’ and ‘b’ coefficients) and UNTRIX classification approaches revealed that the original TRIX index was not efficient enough to demonstrate impacts of excessive nutrient loads on the oligotrophic waters whereas the TRIX-IMS and UNTRIX approaches categorized the inner bay water body to have “eutrophic” status compared to the “oligotrophic” waters of the outer bay.