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Spatial and seasonal variations in δ ¹⁸O and δD values in the River Sava in Slovenia

Ogrinc, Nives, Kanduč, Tjaša, Stichler, Willibald, Vreča, Polona
Journal of hydrology 2008 v.359 no.3-4 pp. 303-312
rivers, surface water, hydrochemistry, stable isotopes, oxygen, deuterium, spatial variation, seasonal variation, watershed hydrology, precipitation, rain, runoff, stream flow, Slovenia
Stable isotope measurements of oxygen and hydrogen (δ ¹⁸O and δD) in stream waters and precipitation were used to investigate hydrological pathways and residence times in the River Sava catchment in Slovenia. δ ¹⁸O and δD values of precipitation exhibited strong seasonal variations. Precipitation is of mixed Atlantic-Mediterranean origin which is also reflected in the isotopic composition of River Sava surface waters. The isotopic content of the river water is dependent on temperature, elevation of the recharge area and amount of precipitation. Spatially, rivers water is ¹⁶O-enriched in the high mountain areas due to higher amount of precipitation, lower temperature and higher elevation of the recharge area, while in the lower part of the River Sava catchments the δ ¹⁸O values are higher. It is also observed that the River Sava responds quickly to precipitation which is reflected in its δ ¹⁸O and δD values and the low residence time estimated in the river. Using an exponential flow model it was calculated that mean stream water residence times varied between 0.4 and 2.1 years. The shortest residence time determined at Savica is connected mainly to the higher amount of precipitation in the upper Sava watershed and the mountains carbonate karst terrain characterized by a higher runoff. The mean residence time in the main stream water of the River Sava was estimated to be 1.32 years and is in a good agreement with the residence time determined using ³H measurements. These data extend our knowledge in understanding the hydrological cycle of the River Sava, the interactions between precipitation, surface water and groundwater and, at the same time, demonstrate the utility of isotope tracers in determining catchments characteristics.