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Stable isotopes as natural tracers of the karst recharge to the tertiary clastic aquifers: a case study of southern part of Ljubljana marsh
Joe Pezdič, - (27/1,1998)
The main purpose of the research was to determine the recharge and storage of groundwater at the southern part of Ljubljana marsh where tertiary aquifers are filled mainly with karst water. Stable isotopes of hydrogen, oxygen and carbon in water or in dissolved species, as well as tritium content in water and precipitation were used as natural tracers to follow the recharge and discharge of surface streams and aquifers. Together with hydrogeological and other chemical evidence they provide useful information about water mass transport, storage, refilling of aquifers and mixing of groundwater. In the aquifers, springs and surface river water d18O varied from -9,65 to -8,82 while dD has the range from -67,4 to -61,2 . Tritium activities are measured from 1,6 to 13,4 T.U.. Long term averages (n = 13 years) for d18O (dD) in Ljubljana is -8,73 (-60,6) and tritium content is 17,5 T.U.. The mean temperature in Ljubljana is 10,03C and average years precipitation amount is 1332 mm. Years 1992-93 have been characterised by low tritium content in precipitation (8,2 for 1992 and 10,6 for 1993) and so important for investigation. The average mean meteoric line for the last 14 years is defined as dD=8,188xd18O+10,66. Temperature correlation vs. oxygen is: d18O=0,254xt-10,78. The above database is discussed in order to evaluate thesis about karst influence on the recharge and storage of clastic sediment aquifers in the Ika delta sediment structure.