Atmospheric water vapor was sampled simultaneously at two heights in the at
mospheric surface layer above a coastal salt marsh near New Haven, Connecti
cut, during June 11-27, 1997, The water vapor samples were analyzed for the
ir mixing ratio, Q, and deuterium isotope ratio, deltaD. The observed SD va
ried in the range of -145 to -89 per mil and was positively correlated with
Q, reflecting the influence of in-cloud condensation and surface evapotran
spiration processes at a regional scale. Both Q and deltaD were, in general
, lower at the upper level, indicating an upward transport of (H2O)-O-16 an
d (HDO)-O-16. The Craig-Gordon model reproduced reasonably well the combine
d effects of equilibrium and kinetic fractionations and atmospheric demand
on the evaporation process. Transpiration of the marsh plants, Spartina pat
ens (Ait.), was a minor component (11%) of the total evapotranspiration dur
ing the experimental period. We also suggest that the relationship between
deltaD and salinity, S, of the marsh surface water can be used to infer the
isotope flux ratio. More data, however, are needed to verify this mass bal
ance approach.