(8b)
IL is the total amount of water input to the lake
by precipitation, runoff, etc. The value of Q L is
the total water output from surface and underground runoff. The value ofE L is the amount of lake evaporation. The value
of δ 18OI,
δ 18OQ andδ 18Oev are the stable isotopic
ratios of oxygen in the inflow runoff, the runoff out of the lake, and
lake evaporation. Assuming that the oxygen stable isotope ratio of
runoff out of the lake is equal to the lake water, usingQ L=I L-E L
and δ 18OQ
=δ 18OL to change the formula 8,
we arrive at formula 9.