Karst aquifers are characterized by high heterogeneity of groundwater flow. The classical study methods such as boreholes, pumping tests, and point observations give important data but cannot be extended to the entire aquifer. However the environmental hydrochemical and stabile isotope methods could give important information about large scale aquifer characterization. Some study examples from Albania, shown in this paper, demonstrate the successful application of the isotope methods, which are more powerful if applied in combination with hydrochemical ones, for the identification of the karst water recharge sources. Among the isotope methods the altitude effect seems to be more indicative for the solution of the problem concerned. For characterising the lithology of karst rocks and the physical aspects of karst aquifers (type of groundwater flow) the combined use of some hydrochemical parameters like the water conductivity, total hardness, ionic ratios rCa/ rMg, rSO4/r/mg, CO2 pressure and the indexes of calcite and (Sic) and of dolomite saturation (Sid), result very useful.
The Prespa-Ohrid lake system is shared between Greece, Republic of Macedonia (FYRO) and Albania. In recent years a water decrease in the Prespa Lake has been recorded. Though it has been established that the water from the Prespa Lake flows into the Ohrid Lake through the Galichica mountain, it is not clear whether this is the main reason for the lake's water loss in recent years. The three main reasons behind the lake's water loss investigated are: (i) underground flow from Prespa to Ohrid Lake, change in weather pattern, anthropogenic factors. Though there were several studies investigating the water level decrease in the lake, so far no conclusion on the reasons behind this phenomenon has been reached. As part of an ongoing research project supported by the NATO Science for Peace (SfP) programme the problem of water loss in the lake has been investigated. Some of the results of this study are presented.
On the borders between FYR of Macedonia, Albania and Greece there are three lakes: Ohrid Lake, and Big and Small Prespa Lakes. Galichica and Dry mountains separate the lakes. Several Projects (Supported by IAEA, NATO, EU, UNESCO and others) have been dealing with the determination of the water balance and the protection of Prespa and Ohrid Lakes with special attention to the explanation of the decreasing of the Prespa Lake water level, in excess of 8m in the last decades. Investigations using Environmental isotopes and artificial tracers showed that Prespa Lake's waters drain through the Galichica and Dry mountains into Ohrid Lake. By using an appropriate model, relevant hydrogeological, hydro meteorological data, satellite images and a computer program which implements an adequate recursive and exponential equations, the volume of the underground aquifer below Galichica Mountain and the volume of the Prespa Lake have been calculated.
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