Tracing Water Sources Along the Brazos River Alluvial Aquifer with 234U/238U Activity Ratios and Uranium Concentrations
Abstract
The combined use of 234U/238U activity ratios and uranium concentrations can be
used to trace water sources within a hydrological system. Additionally, the specific
uranium concentration and isotopic signature of each source can be applied to mixing
calculations to estimate the relative contribution of each source in a river. 234U/238U
activity ratios and uranium concentrations were measured over a 6-month period in the
Brazos River watershed along the Brazos River Alluvial Aquifer to determine where
water in the Brazos River is sourced from and to estimate groundwater discharge to the
Brazos River.
Results from this study indicate that lithology within the Brazos River watershed
affects 234U/238U activity ratios and uranium concentrations along the studied stretch of
river as there is a change from carbonate rocks to siliciclastic rocks downstream and an
associated change in 234U/238U activity ratios. Rain was found to have a negligible effect
on 234U/238U activity ratios of sources within the area, and only dilutes the concentration
of uranium in these sources. 234U/238U activity ratios and uranium concentrations
suggest water in the Brazos River near Bryan/College Station, Texas is sourced from
Lake Whitney, groundwater, and tributaries. Groundwater appears to discharge from the
alluvial aquifer to the river at a steady rate with slight increases in groundwater
contributions as discharge increases in the Brazos River. This study demonstrates the
utility of uranium as a natural tracer of water sources.
Citation
Prince, Benjamin Hays (2017). Tracing Water Sources Along the Brazos River Alluvial Aquifer with 234U/238U Activity Ratios and Uranium Concentrations. Master's thesis, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /169592.