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 m(3)/s), or through the travertine (e.g. the Dudenbasi Spring, 18 m(3)/s) and underneath it (un named submarine springs, unknown discharges). In an attempt to identify the hydraulic connections between the various outlet points, groundwater was a nalyzed for stable and radioactive isotopes, CFCs and He. The upgradient sp rings, belonging to the Kirkgozler-Dudenbasi system, were proven to be a mi xture of recent and older water on the basis of their low C-14 values (12-2 2.4 pmc), their exceptionally high He content (429-991 mu cc/kg) and He-3:H e-4 (R:Ra) ratios (1.471-2.602) and their measurable H-3 and CFC contents ( 1.9-5.9 TU and 0.84 to 3.27 pmoles/kg, respectively). The older component p robably contains an even lower amount of modern C. However, the undersatura tion of the mixture with respect to calcite, its high CO2 content (up to 83 mg/L) and its enriched C-13 values (-2.2 to -4.1 parts per thousand) sugge st intensive water/rock interactions, which would contribute C-14-devoid bi carbonates to the solution. Downgradient springs discharging along the Medi terranean coast contain groundwater contributions from higher altitudes, as evidenced by their depleted delta(18)O and delta D composition with respec t 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 H-3 (3.4 to 8.4 TU) a nd C-14(32.7-63.6 pmc) contents, atmospheric He (43-82 pmoles/kg), R:Ra val ues (1.006-1.198) and CFC contamination of the water. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.