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An Isotope and Energy Balance Study of the Snow-Melt Process (Abstract)

Energy, mass and isotope balances in the snow-melt process have been studied during the spring of 1984 at a forested site on the property of Atomic Energy of Canada Limited at Chalk River, Ontario. For the whole of the period, continuous measurements were made of the variables controlling the energy balance over the surface of the snowpack. The volume flow rate of water out of the base of the snowpack was measured using a 25 m Iysimeter. A water sample was taken every two hours throughout the thaw for chemical and isotopic analysis. The deuterium content of preclpltation is directly related to air temperature at time of precipitation. As a result there is a strong seasonal fluctuation of deuterium in precipitation and spring rain has a significantly higher deuterium concentration than the melting snowpack accumulated from the winter's snowfall. Thus isotopic measurements afford a means of differentiating on a molecular basis between snow-melt and rain flow-through in the drainage water from a melting snowpack . It is of value to compare estimates of the proportions of snow-melt and rain flow-through in drainage water derived from isotope measurements with those obtained from energy balance considerations. Analysis of energy, mass and isotope balances has been done for three example periods: (i) snow-melt only, (ii) snow-melt plus modest rainfall, (iii) snow-melt plus dominant rainfall. The first example period demonstrates the overall energy balance conditions during snow-melt in a deciduous forest. The dominant energy flux is Q* (net all-wave radiation). Our data show that Q* generates about 90% of snow-melt under most atmospheric conditions, and that the long-wave portion CL *) of net all-wave may become very large in the forest during snow-melt. Because of the reduction of wind speed at the forest floor, and because of the conditions of extreme atmospheric stability which invariably occur over a melting snow-pack, the turbulent exchanges CH and LE; sensible and latent heat) are very small. The maximum hourly melt rate due to Q* in the first example, is 3.6 mm h1, and the maximum due to H + LE is 0.12 mm h1. At a maximum, H + LE account for less than 13% of daily snow-melt.