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The Meriç River is the most important aquatic ecosystem in the Thrace Region of Turkey and the longest river of the Balkans. In the present study, water quality of the Meriç River in the rainy season was investigated and the pressure of the Tunca and Ergene rivers on the system was evaluated by a statistical approach using cluster analysis (CA). Water samples were collected from five stations (two of them from the downstream the Tuna and Ergene and three from the Meriç) in spring 2015. A total of 19 physical, chemical, and biological water quality parameters -including temperature, dissolved oxygen, percentage of oxygen saturation, pH, conductivity, TDS, salinity, turbidity, nitrate, nitrite, ammonium, phosphate, sulfate, chemical oxygen demand, biological oxygen demand, total carbon, total inorganic carbon, total organic carbon, and cyanide -were measured. According to detected data, pollution levels of the investigated rivers were as follows; Ergene River > Tunca > Meriç River. It was also determined that the Ergene and Tunca reduce the water quality of the Meriç significantly after they fall. And also according to the results of CA, three statistically significant clusters were formed, which corresponded to the Ergene (Cluster 1); upstream and midstream of the Meriç (Cluster 2), and downstream of the Meriç and Tunca (Cluster 3).

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Gala Lake National Park that has an international importance is one of the most important wetland ecosystems for Turkey. As same as many aquatic habitats, Gala Lake is under a significant anthropogenic pressure originated from agricultural activities conducted around the lake and from industrial discharges by means of Ergene River. The aim of this study was to evaluate the sediment quality of Gala Lake and Irrigation Canal by investigating some toxic element accumulations (As, B, Ni, Cr, Pb, Cd, Zn and Cu) from a statistical perspective. Pearson Correlation Index (PCI) and Factor Analysis (FA) were applied to detected data in order to determine the associated contaminants and effective factors on the system. Potential Ecological Risk Index (RI) and Biological Risk Index based sediment quality guidelines (mERM-Q) applied to detected data in order to assess the ecological and biological risks of heavy metals in the ecosystem. Also Geographic Information System (GIS) technology was used to make visual explanations by presenting distribution maps of investigated elements. According to the results of PCI, significant positive correlations were recorded among the investigated toxic elements at 0.01 significance level. According to the results of FA, two factors, which were named as “Agricultural Factor” and “Industrial Factor”, explained 86.6% of the total variance. According to the results of Potential Ecological Risk Index, cadmium was found to be the highest risk factor and according to results of Biological Risk Index, nickel and chromium were found to be the highest risk factors for Gala Lake and Irrigation Canal. As a result of the present study, it was also determined that heavy metal contents in sediments of Gala Lake National Park reached to critical levels and the system is intensively under effect of agricultural and industrial originated pollution.

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