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Hydrochemical Characteristics of the Large Karst Springs in the Catchment of Mesta River (Bulgaria)

Mesta river is a cross-border river with Greece, whose catchment area includes parts of Rila, Pirin and the Rhodope Mountains. The karst is developed in pre-Paleozoic marble that forms isolated outcrops with different basins. The largest of them forms two alpine karst basins located in Northern Pirin and Slavyanka Mountains. In the Rhodopes region, the marble outcrops are fragmented and embedded in non-karstic rocks. They are drained from springs with relatively low flow rates. The largest karst springs drain different hydrodynamic zones of the karst massif of Northern Pirin. From the karst basin of Slavyanka Mountain, only the large subthermal spring near the village of Musomishta falls into the catchment area of the Mesta river. The data on the chemical composition of some of the karst springs are summarized, paying attention to the largest of them. An analysis of the changes in the chemical composition and comparison is made. The changes of the hydrochemical parameters of the springs draining different vertical zones in Northern Pirin are compared. The obtained results prove that the main role in the formation of the chemical composition of karst waters has natural factors - interaction between water and marbles. It was found that the waters are unsaturated to carbonate minerals, which proves that even now there are active processes of karst formation.