Hydrogeochemical properties of Çal Cave and its vicinity: Development and consequences of karstification in Düzköy (Trabzon, NE Türkiye)

Abstract

Çal Cave, through which an underground river runs, was formed through the karstification of the neritic limestones that make up the Şahinkaya Formation, located between the neighbouring districts of Çayırbağı and Çalköy in Düzköy (Trabzon). The purpose of this study was to analyse the hydrogeochemical characteristics of samples collected from Çal Cave and the waters believed to supply it to determine their potential origins. Water samples were collected from nine locations during the wet and dry periods. After measuring the physical parameters of the samples, major anion–cation and trace element analyses were performed. When the parameters were compared with both WHO and Turkish standards, it was determined that they were within the limit values specified in the relevant regulations. Schoeller and Piper diagrams suggest that these waters are fed by the same origin and can be classified as a Ca-HCO₃ water type. Water-saturated zones were identified through electrical resistivity tomography sections that analysed the areas around the sampling sites. Finally, a comparison of the water quality data of water samples from Çal Cave during the dry season, published by Ofluoğlu in 1993, and this study's dry season water quality data revealed a decrease in the concentrations of Ca²⁺, Mg²⁺, K⁺, Cl⁻ and SO₄²⁻. The reason for this decrease over the past 29 years is likely the increased number of entryways where surface waters feed the cave.