GEOGENIC TRACE ELEMENT ENRICHMENT IN THE NORTHERN DEVELI CLOSED BASIN (KAYSERI, TURKEY)

This study was carried out to determine the origin of the trace element enrichment in the groundwaters of the Develi Closed Basin (DCB). The study area is located in the Kayseri province of Central Turkey towards the northern part of the DCB. The DCB hosts one of the most important bird paradises of Turkey, Sultansazligi wetland which is protected since 1994 according to the International Ramsar Agreement. The study area is approximately 760 km². Mount Erciyes, a volcanic mountain and the highest peak in Central Anatolia (3916 m), is located within the borders of the study area. The geologic formations of volcanic origin formed during the latest stages of Mount Erciyes volcanism in between the Miocene and Quaternary outcrops in the area. Groundwater occurs under both unconfined and confined conditions in the altered and fractured parts of volcanic rocks. In order to determine the source of the trace element enrichments in the groundwater, water samples were collected from 10 groundwater wells and 5 springs in two different seasons (September 2013 and March 2014). The major ion and trace element analyses (Pb, Zn, Cr, Mn, Fe, Cu, Cd, As, B) were carried out in State Hydraulic Works Laboratories in Kayseri, Accordingly, the chemical characters of the waters in the area are of Ca-Mg-HCO₃, Na-Cl-HCO₃types. The chemical character of some of the samples show variations between wet and dry seasons due to the water-rock interaction especially during the wet season. Concentrations of metals (As, B, Fe, Pb, Zn and Cu) in some of the water samples exceed the World Health Organization Limits. For instance, As concentrations are up to 593 µg/l and 774 µg/l in dry and wet seasons, respectively. The Fe concentrations are highly variable in some samples in different seasons and the mean Fe concentrations were almost double between dry (mean 867 µg/l) and wet (mean 1443 µg/l) seasons. The source of these heavy metals occurring at high concentrations in some of the samples is attributed to geogenic sources. Since the volcanic rocks of the Erciyes volcanism are products of a fast cooling magma, they are highly heterogeneous. The heavy metals naturally present in these rocks incorporate into groundwater during the water-rock interaction occurring especially around the altered parts of the volcanic rocks.