Using 180/160 data to examine the mixing of water masses
in floodplain wetlands
Wesley S. Hardegree1, David B. Wenner1, John F. Dowd1 and Kenneth W. McLeod2
1Department of Geology, University of Georgia, Athens, GA 30602, USA;
2Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA
Keywords: backwater, floodplain, groundwater, oxygen isotopes, Savannah
Oxygen isotopic data were used to assess how far waters from the Savannah
River, a major river in the Southeastern United States, backed up and inundated
the wetlands along a small Coastal Plain tributary during a flood. This approach
worked because the water of this tributary, Upper Three Runs, had an oxygen
isotopic composition (§180 = -4.9 %o) distinct from Savannah River water (§180
= -3.2 %0).
Two sample surveys were taken from the mouth of Upper Three Runs to 2 km
upstream. Waters were isotopically uniform along the length of the sample transect
when both river and tributary water levels were below bankfull. Visual estimates
of turbidity taken when both the river and tributary overflowed their channels and
inundated adjacent wetlands indicated that Savannah River water extended about
300 meters up the tributary channel. In contrast, the isotopic data indicated that a
mixing zone of river and tributary waters extended about 1100 meters upstream.
Although this mixing zone was documented only in the channel of Upper Three
Runs, it probably extended into adjacent parts of the riparian wetlands potentially
affecting ecological processes due to the differing water quality. This study was
conducted in a single river-tributary system and the approach is probably
applicable in other large rivers.
SREL Reprint #1995
Hardegree, W.S., D.B. Wenner, J.F. Dowd, and K.W. McLeod. 1995. Using
18O/16O data to examine the mixing of water masses in floodplain wetlands.
Wetlands Ecology and Management 3:189-194.
To request a reprint