Understanding water characteristics and arsenic contamination of Lower Bakırçay Basin (LBB) and its coastal wetland (Western Turkiye): from Bergama (Pergamum) to Çandarlı (Elaia) by hydrogeochemical tools and stable isotope signatures

Bakırçay Basin is one of the largest and most productive basins in Turkey in terms of geothermal energy, history, mining, agriculture, and tourism. In this study, the lower part of the Bakırçay Basin was extensively examined using hydrogeochemical tools, encompassing 27 different water sample points in the basin, in alignment with the United Nations' 2030 sustainable development goals that focus on access to safe drinking water for all and climate action for carbon emissions. From the higher zones of the basin towards the coastal wetland, EC values increase from 212 to 26500 µS/cm. Again in the same direction, water types are Ca-Mg-HCO3 in hilly areas and Na-Cl at the coastal wetland. Salt marshes, which are the silent heroes of carbon sequestration, are the most important element of the Bakırçay coastal wetland. Irrigation water evaluation has also been made for agriculture, which is widespread in the basin. Except for the salty waters in the wetland, waters are suitable for irrigation. A contamination investigation was conducted in the waters with the aim of clean drinking water. As and Mn contamination, which exceeds the standard values, has been detected in the Bakırçay river and its tributaries, especially from the mining sites in LBB. The arsenic content of water in the study area varies between 2 and 62.2 ppb. Additionally, the study identified As(III) species, which is 60 times more toxic than As(V), in the study area. Stable isotope values (δ18O and δD) of waters in the basin are from - 6.66 to 1.43‰ and - 36.4 to 5.8‰, respectively, and all waters are of meteoric origin. It is essential to emphasize the importance of controlling mining activities in the basin, halting the construction of the port that will destroy the carbon sequestration coastal wetland, and instead, transforming it into a recreation area, the significance of which is now understood during the COVID-19 pandemic.