During 1965-1967 the snowmelt runoff in a small mountain basin in Northern Czechoslovakia was studied by measuring the tritium and oxygen-18 content of precipitation, snowpack, and runoff, in addition to an improved degree-day method which was used as a standard tool. The results showed that about two-thirds of the meltwater infiltrated to the soil, and the displaced water recharged during the previous years toward the stream channels. The tritium content of the baseflow and the subsurface runoff indicated that the mean residence time of the subsurface water in the basin was approximately 2.5 years with a standard deviation of 1.25 years. The volume of the subsurface storage was estimated to be 2.6 X 106 m s. The oxygen-18 content of snow samples was in agreement with the tritium results on the relative contribution of the meltwater and subsurface runoff to the total runoff from the basin. x At present with the Institute of Nuclear Techniques, Academy of Mining and Metallurgy, Cracow, Poland. ' At present with the Institut fiir Schnee-und Lawinenforschung, Dayos, Switzerland. bined with environmental isotope techniques to investigate all phases of the snowmelt-runoff process.An evaluation of data obtained in the winter and snowmelt seasons of 1966 and 1967 is presented in this paper. This study illustrates the application of isotope techniques to problems of snow hydrology and it is hoped the study will stimulate the use of these techniques. CHARACTERISTICS OF THE BASINThe Modry Dul representative basin is situated in the eastern part of the Krkonose mountains in northern Bohemia (15ø42'E and 50ø43 'N (Figure 1)). The surface area is 2.65 km •, of which about 70% is mountain meadows and 30% is spruce forest. The mean altitude of the basin is about 1300 meters above sea level with a uniform distribution of altitude between the lowest point (1000 meters) and the highest point (1554 meters). Geologic conditions are characterized by rely-110 ß ß ß ß ß ß BASEFLOW --11.5 ß ß ß ß ßß ß ß Oß O0 Oß 0 / o• o o //o ß ß ß ß ß -12.3

This article presents the results of measurements of the isotopic composition and concentration of atmospheric carbon dioxide, performed on air samples from Kraków (Southern Poland) in different seasons of the year. A simple isotope mass balance model has been applied to determine the contributions of different sources of CO2 to the urban atmosphere of Kraków city: the latitudinal/regional background, biospheric contributions and anthropogenic emissions. The calculations show that during the summer and early autumn the dominant contribution to local CO2 peaks is the biosphere, making up to 20% of atmospheric CO2 during the nocturnal temperature inversion in the lower troposphere. During early spring and winter, anthropogenic emissions are the main local source.

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Determination of underground production of radionuclides important in 'dating' groundwater and in problems related to underground disposal of high-level radioactive waste disposal is discussed. For estimation of natural production of radionuclides the neutron energy spectrum in the rock must be calculated based on the rock chemical composition and its physical parameters. Details on several interesting radionuclides produced in spontaneous fission of uranium and in reactions with underground neutrons are given.