Abstract
Abstract. Stable water isotopes are widely used in ecohydrology to trace the transport,
storage, and mixing of water on its journey through landscapes and
ecosystems. Evaporation leaves a characteristic signature on the isotopic
composition of the water that is left behind, such that in dual-isotope
space, evaporated waters plot below the local meteoric water line (LMWL) that
characterizes precipitation. Soil and xylem water samples can often plot
below the LMWL as well, suggesting that they have also been influenced by
evaporation. These soil and xylem water samples frequently plot along linear
trends in dual-isotope space. These trend lines are often termed “evaporation
lines” and their intersection with the LMWL is often interpreted as the
isotopic composition of the precipitation source water. Here we use numerical
experiments based on established isotope fractionation theory to show that
these trend lines are often by-products of the seasonality in evaporative
fractionation and in the isotopic composition of precipitation. Thus, they
are often not true evaporation lines, and, if interpreted as such, can yield
highly biased estimates of the isotopic composition of the source water.
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
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