Hydrochemistry and groundwater quality in a semiarid calcareous area: an evaluation of major ion chemistry using a stoichiometric approach.

This study is a wide-ranging evaluation of groundwater within the calcareous semiarid area, Gaziantep in southeast Anatolia, Turkey. The resulting water chemistry data (1) explains the interactions between rock and water, (2) evaluates the quantitative relationships between chemical species (major ions), (3) separates hydrochemical facies, (4) provides information on current water quality for multiple uses, and (5) acts as a benchmark for future research. Relationships between ion concentrations (as meq/L) were analyzed through linear modeling and calculation of coefficients of determination (R2). Stoichiometric calculations were employed to determine the quantitative relationships between ions in groundwater. Calculations between (Ca2++Mg2+) and HCO3- indicated that, even at different concentrations of the total alkaline earth metal ion (M2+), the relative percent remained at 72% for all samples. The majority of Ca2+, Mg2+, and HCO3- ions in groundwater were derived from weathering of calcite, the most common mineral in the local geology. Weathering of dolomite was also important to the contribution of ions in some areas. Ca-HCO3 was found to be the dominant water type for 81% of raw samples; a mixed water type was found in 17% of the samples. The major dissolved components of groundwater are, therefore, Ca(HCO3)2 and, to a lesser degree, Mg(HCO3)2.The sampled groundwater was generally found to meet drinking water quality guidelines for most of the physicochemical quality properties for which standards are available, and with regard to concentrations of Mg2+, Na+, K+, Cl-, SO42-, NO2-, and NH4+. However, NO3-, Ca2+, and HCO3- concentrations in several groundwater samples were in excess of maximum acceptable concentrations (MACs).

Fluid pathways identified beneath Narli Lake (Central Anatolia) show the geothermal potential of former volcanoes.

We investigated the volcanic Narli Lake in Central Anatolia combining high-resolution bathymetry and geochemical measurements. In this study, we present it as proof of a new concept to verify fluid pathways beneath lakes integrating the structure of the geothermal reservoir into the surrounding tectonic frame. We recognized dextral faults fracturing inherited volcanic formations and thus generating highly permeable zones beneath the lake. At intersection points of faults, reservoir fluids discharge from deep holes as imaged by the high-resolution bathymetry at the bottom of the Narli Lake. Onshore, the tectonic setting also generates both extensional and compressional structures. Extensional structures result in extensive fluid discharge through hot springs while compressional structures do not discharge any fluid. The water of the lake as well as in the hot springs is highly saline and has relatively high concentrations of Cl, HCO3, SO4, Na, Ca, Mg, and Si. In several hot springs, we observed mixtures of high-saline fluids having a deep origin and low-saline shallow groundwater. We observed discharge into the lake by gas bubbles, which contain probably CO2 or H2S. Mineral precipitation indicates a carbonatic source at the lake bottom and along the shoreline. Extensive travertine precipitation also occurs near hot springs along the nearby extensional zone of Ihlara Valley. In summary, the composition of fluids and minerals is controlled by water-rock interaction through the volcanic and carbonatic rocks beneath this volcanic lake.