We present the results of a water circulation study in a small drainage basin in a mountainous area of a complicated structure. Two types of waters were found in the basin; the sulphate waters were linked to gneiss and crystalline schist rocks, while the bicarbonate waters were linked to a marble interbed. The paper looks at a number of water circulation and mixing scenarios and discusses the origin of the bicarbonate waters. Measurements and calculations helped to identify two karst water circulation systems within the marble interbed that were probably not connected to each other. The primary system collects waters migrating via fissures from a non-carbonate section of the drainage basin above. Initially these waters are of the sulphate type: acidic and corrosive to the carbonate rocks. After passing into the marble interbed, they gradually assume a bicarbonate nature by becoming saturated with products of the chemical dissolution of carbonate rocks. This karst system is drained by springs. The other system begins in a sinkhole that intercepts a portion of the stream discharge (or all of it during extreme droughts) and ends with dispersed outflows directly into the channel lower down in the drainage basin.

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