Typological and qualitative characteristics of Greek-interregional rivers
The catchments of the interregional rivers (I.R.) entering Greece cover an area of approximately 98000 km2, of which only 14% belongs to Greece, while their contribution to the country’s freshwater runoff reach 40% (18 km3/a). Geologically, the I.R. catchments are marked by their high percentage of acid silicates. I.R. show hydrochemical similarities, except for Evros, which is highly polluted. Compared to the other major Greek rivers, I.R. are the most polluted, with the Evros at the top, followed by the Axios. The main factors controlling their composition are climate, pollution and catchment geology. Inter-annual qualitative variations are controlled by seasonal climatic variations, which govern evaporation, groundwater contribution to river flow, dilution and flushing. A long-term salinisation of river water is attributed to climatic and anthropogenic impact. The I.R. transfer approx. 6,63 Μ t dissolved solids to the sea annually. Regarding the inputs of pollutants into the sea, they transfer over 70 % of the potassium, nitrate and dissolved organic carbon of the total load carried by major Greek rivers (78% of total Greek surface runoff), whereas for phosphate and sulphate the percentages reach 89 and 78.