SEASONAL VARIATIONS OF ORGANIC MATTER AND NUTRIENTS IN THE NORTHEAST MEDITERRANEAN ( BAY)

Emine Erdogan 1*, Süleyman Tugrul 2 and Özden Bastürk 1 1 Mersin University, Faculty of Fisheries - [email protected] 2 Middle East Technical University, Institue of Marine Sciences, 33731, Mersin,

Abstract In the present study,4 field studies,in the April 2010 – February 2011 period,were conducted in the eastern region of Mersin Bay extending from Mersin city up to Seyhan River delta.In the river-fed coastal waters, nitrate values were high (1.1 -9.2 µM);the low phosphate(0.06-0.16 µM)values result in higher N/P ratios (35-50) in nearshore waters.Surface total phosphorus, chlorophyll-a and particulate organic matter displayed similar spatial distributions, decreasing 5-10 times in the offshore waters, exhibiting seasonal variations. POM values were as high as 10.9-88.4 µM for POC, 1.5-8.3 µM for PON and 0.05-0.27 µM for PP in the polluted shallow zone, with the POC/PON: 7.1-10.6 and PON/PP: 18-35 ratios.These ratios generally ranged between 7 and 10 as the concentrations decreased markedly in the oligotrophic offshore waters of the bay.

Keywords: Eutrophication, Nutrients, Particulates, Mersin Bay

Shelf waters of NE Mediterranean (Cilician basin) have been polluted by increased steadily to 2.7 µg/L level in the river-fed nearshore waters. Apparent discharges of the major rivers (Seyhan, Ceyhan) and domestic wastewaters of increase in the POM conetrations coastal waters with low C/N ratios indicate the big cities in the region. Therefore, eutrophication phenomena have increased that the enhanced eutrophication dominates the POM pool in the inner shelf in the Mersin bay shallow waters fed by polluted river and domestic water compared to the POM of regenerative origin in the open sea during spring- discharges. On the other hand, open surface waters of the Eastern autumn period. Particulate P and PO4 constituted merely 10-35 % and 8-25 % Mediterranean is a typical example for the oligotrophic seas [1-2]. This study of TP pool in the nearshore; the rest by DOP which dominate in the TP pool in aims to assess inpacts of land based inputs on the distributions of the euphotic zone of the open sea. eutrophication- related biochemical parameters in the bay, covering the affected coastal zoen and offshore waters (Fig. 1). Four field surveys were conducted by R/V BILIM during the April, 2010-February, 2011 (funded TUBITAK within 107G066 project). Conventional methods were followed in the measurements of chemical parameters. Concentrations of dissolved inorganic nutrients, POM, biomass, CHL-a were expectedly high in the nearshore waters of the bay fed by nitrate-rich rivers (with high N/P) and domestic wastewater discharges. Impacts of land-based inputs weaken markedly in the offshore waters due to limited water exchanges between the shallow inner bay and deeper (>50 m) offshore (Fig. 1). Typical surface distributions of nitrate and CHL-a (algal biomass indicator) in the bay show the highly impacted water body in the nearshore zone. In spring-autumn period, surface nutrient values were consistently low in the central and outer bay waters (0.02-0.05 µM for PO4 and 0.05- 0.67 for NO3) with relatively low N/P molar ratios (8-15) which increased up to 35-50 in the nearshore waters fed by river discharges.

Fig. 2. Surficial distribution of POC in the bay in April 2010.

References 1 - Yilmaz A., Tugrul S. The effect of cold- and warm- core eddies on the distribution and stoichiometry of dissolved nutrients in the northeastern Mediterranean, Journal of Marine Systems, 16, 253-268, (1998).

2 - Krom M. D., Woodward E. M. S., Herut B., Kress N., Carbo P., Mantoura R. F. C.,Spyres G., Thingstad T. F., Nutrient cycling in the south east Levantine basin of the eastern Mediterranean:Results from a phosphorus starved system, Deep-Sea Research II, 52, 2879-2896, (2005).

Fig. 1. Surficial distribution of nitrate in the bay in April 2010.

Surface water N/P ratios appears to decrease in spring-autumn period due to decreasing nitrate values of the surface waters. Surface CHL-a concentrations, as low as 0.05-0.15 µg/L in offshore waters displaying oligotrophic properties,

184 Rapp. Comm. int. Mer Médit., 40, 2013

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