ESTIMATION OF EVAPORATION RATE OF SURFACE WATER USING HYDROGEN AND OXYGEN ISOTOPIC RATIOS

Abstract

Both evaporation rate and temperature can be estimated from δD and δ18O values of water before
and after evaporation. From laboratory evaporation test results of water under uniform temperature condition,
relations between evaporation rate, δD and δ18O values of water before and after evaporation were expressed at
each temperature as the following equations, Y = -0.44X1+ 12.67X2 + 50.90 : 20 degrees C, Y = 0.30X1+ 1.88X2
+ 41.86 : 25 degrees C, Y = -1.70X1+11.80X2+ 7.74 : 30 degrees C, Y = -0.11X1 + 6.37X2+ 34.74 : 35 degrees
C, Y = -0.71X1 + 6.82X2+ 35.11: 40 degrees C and Y = -0.17X1 + 4.94X2 +30.05 : 50 degrees C. Y is evaporation
rate. X1 is δDae – δDbe – 51.3. X2 is δ18Oae - δ18Obe -7.52. δDbe and δDae are δD values of water before and
after evaporation. δ18Obe and δ18Oae are δ18O values of water before and after evaporation. Evaporation
temperature can be also estimated from δD and δ18O values of water before and after evaporation. Relation was
expressed by the equation, (δDae – δDbe – 51.3) / (δ18Oae - δ18Obe -7.52) = -0.064 × temperature + 7.45. From
δD and δ18O distribution map of water before and after evaporation, both evaporation rate and temperature can be
also estimated.