La. Martinelli et al., USING STABLE ISOTOPES TO DETERMINE SOURCES OF EVAPORATED WATER TO THEATMOSPHERE IN THE AMAZON BASIN, Journal of hydrology, 183(3-4), 1996, pp. 191-204
The return of water in vapor form from the land to the atmosphere, via
plant transpiration and evaporation, is fundamental for the maintenan
ce of the regional water cycle in the Amazon basin. Whereas transpirat
ion, the dominant process, has the extensive vegetation cover as a lar
ge single source, evaporation can have several sources, and their rela
tive importance and location are poorly known. The isotopic compositio
n (delta(18)O and delta D) of water from various sources was used to s
ee whether or not specific sources of water vapor to the atmosphere co
uld be determined. It is well established that natural waters fall on
a line called the meteoric water line (MWL; the regression of delta(18
)O x delta D), With slope equal to eight and an intercept equal to ten
. When a water body loses water via evaporation the slope become small
er than eight, typically 5-6. We estimated the slope of the regression
of delta(18)O x delta D for several potential sources. We analyzed 12
73 samples: 500 of rainfall, 409 of river water, 134 of lake water, 16
4 of soil water, 40 of throughfall and stemflow water, and 26 of shall
ow ground-water. We found that large rivers and lakes are likely contr
ibutors of evaporated water to the atmosphere. However, as they cover
only a small area of the basin, other sources are needed. Probably, ev
aporated water originates from several small sources that were not det
ected by the isotopic composition of our data.