Separation of groundwater-flow components in a karstified aquifer using environmental tracers

Groundwater discharges from the intensively karstified Taurus Mountains to the Mediterranean Sea, either along the contact zone between the mountains and the Travertine Plateau (the Kirkgozler Springs, 15 m³/s), or through the travertine (e.g. the Dudenbasi Spring, 18 m³/s) and underneath it (unnamed submarine springs, unknown discharges). In an attempt to identify the hydraulic connections between the various outlet points, groundwater was analyzed for stable and radioactive isotopes, CFCs and He. The upgradient springs, belonging to the Kirkgozler–Dudenbasi system, were proven to be a mixture of recent and older water on the basis of their low ¹⁴C values (12–22.4 pmc), their exceptionally high He content (429–991 μcc/kg) and ³He:⁴He (R:Ra) ratios (1.471–2.602) and their measurable ³H and CFC contents (1.9–5.9 TU and 0.84 to 3.27 pmoles/kg, respectively). The older component probably contains an even lower amount of modern C. However, the undersaturation of the mixture with respect to calcite, its high CO₂ content (up to 83 mg/L) and its enriched ¹³C values (−2.2 to −4.1‰) suggest intensive water/rock interactions, which would contribute ¹⁴C-devoid bicarbonates to the solution. Downgradient springs discharging along the Mediterranean coast contain groundwater contributions from higher altitudes, as evidenced by their depleted δ¹⁸O and δD composition with respect to the local precipitation; however, a larger portion of the recent water component could be contributed from direct precipitation on the travertine. This larger component is reflected in the increased ³H (3.4 to 8.4 TU) and ¹⁴C (32.7–63.6 pmc) contents, atmospheric He (43–82 pmoles/kg), R:Ra values (1.006–1.198) and CFC contamination of the water.