Hydrogeochemical fingerprints of a mixohaline wetland in the Mediterranean: Güllük coastal wetland systems- GCWS (Muğla, Turkey)

Authors: ADİLE MELİS SOMAY ALTAŞ

Abstract: The Güllük coastal wetland system (GCWS), which is located at the contact point of the Menderes Massif and Lycian Nappe, consists of both brackish karstic [Güllük Lagoon wetland (GLW)] and saline [Boğaziçi-Tuzla (Bargylia) coastal wetland (BTW)] ecosystems in western Turkey, and is under protection as a national wetland of importance. This area is important for its unique wetland features, aquaculture, tourism, agriculture, Bodrum airport, and Güllük port facilities. The aim of this study was to evaluate the GLW and BTW, both hydrogeologically and hydrogeochemically, for the first time together. The mixohaline GCWS is recharged from precipitation, streams, and brackish karstic springs. The electrical conductivity (EC) values of Limni Lake and the Tuzla salt pan were measured as 15,330 and 41,000 μS/cm, respectively. The EC value of the brackish karstic springs was ~17,310 μS/cm. From the coast to inland, the mixing ratio increases to a maximum of 45% in Savranköy Spring, which discharges from the contact point between Milas Formation and alluvium. The relationship between Na-Cl, SO₄-HCO₃, and Mg/Ca-Cl showed a weathering by ion exchange and/or seawater intrusion process. All of the groundwater samples comprised NaCl water. In parallel with these results, the diagrams of Gibbs et al. supported the same seawater intrusion phenomena. Brackish karst springs first roseand then fell below sea level with epirogenic movements during the geological period, and therefore, karstification progressed. The samples were oversaturated with calcite, dolomite, and quartz, whereas they were undersaturated with gypsum and halite. The Al, Cu, and Zn values of some of the water samples exceeded the tolerance limit of aquatic life standards. When the samples were evaluated in terms of irrigation water, brackish springs, and streams at Avşar and located near the aquaculture farm, Lake Limni and saltpan had a harmful effect on the plants due to their high Na concentration. These results suggested that the wetland was vulnerable because it was both in a sensitive karstic and a lagoon area. Hydrogeological protected zones should be determined to ensure the sustainability of groundwater resources and provide the economy of the country.

Keywords: Wetlands, hydrogeochemistry, hydrogeology, Güllük, Mediterranean, Turkey

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