TEMPORARY HYDROGEOCHEMICAL INVESTIGATION ON A HYPERSALINE LAKE: LAKE ACIGÖL, DENIZLI, TURKEY

We present the first detailed temporary hydrogeochemical study of Lake Acıgöl, a closed, saline, and alkaline lake located in a semi-arid region of Turkey. This lake has no outflow except by evaporation, and a unique process that controls the lake’s hydrochemistry is the continuous dissolution of soluble salts during wet seasons. The progressive evaporation of lake water in the dry season has increased the concentrations of Na, Mg, Cl, and SO₄; Ca, SO₄, and HCO₃ have been depleted via autogenic gypsum and carbonate precipitation. A lake column profile including surface and bottom samples was collected at a depth of 1.5 m between early June (wet season) and late September (dry season) 2010 and 2012. Spring and well waters were also sampled from the lake drainage basin. During the wet season, the anionic composition of lake waters is characterized by various concentrations of Cl and SO₄. Na and Ca are the dominant cations in this lake; Lake contains Mg and K in different proportions. The TDS of the 100 samples ranged from 31.97–45.69 g/l, and pH values were largely in the range of 8.1–9.97. In contrast to the wet season, the dry season is characterized by high salinity due to the salt production and meteorological conditions such as low precipitation and evaporation. The REE concentrations of Lake Acıgöl were also determined, along with the major solute chemistry, in order to investigate REE distribution and speciation in the high-pH waters. Dissolved REE concentrations of Nd for the 91 water samples (mean: 0.04 ppb, max=1.051 ppb) were typically lower than values the obtained for the saline waters of playa system lakes in the world. Lake Acıgöl is saturated with respect to carbonate minerals such as calcite, aragonite, dolomite, magnesite and gypsum. Our geochemical mobility coefficient results that major elements tend to accumulate in secondary phases, which are consolidated by secondary mineral precipitation and sorption processes. Na, which has a large geochemical mobility coefficient value, tends to stay solubilized in water. The geochemical mobility coefficients of Ca decrease with increasing TDS. Oxygen isotope (d¹⁸O) values of the water samples showed a strong positive correlation with electrical conductivity values (R²=0,78), which supports the effect of evapoconcentration process on the evolution of the lake brine.