Water Resources Research Act Program

Details for Project ID 2007TX269B

Carbon isotopic measurements of dissolved inorganic carbon: A new tool to assess groundwater-river exchange in the Brazos River Basin

Institute: Texas
Year Established: 2007 Start Date: 2007-03-01 End Date: 2008-02-29
Total Federal Funds: $5,000 Total Non-Federal Funds: $10,000

Principal Investigators: Fenwei Zeng, Caroline Masiello

Abstract: The isotopic composition (14C and 3C) of dissolved inorganic carbon (DIC) is a potential tool to assess groundwater discharge to rivers where groundwater is exposed to carbonates. In these systems DIC 14C and 3C of river water sources are significantly different (groundwater: 14C5003C10surface runoff: 14C603C15 making water from carbonate reservoirs easily identified. Limestone is common in aquifers upstream of Bryan but absent in aquifers downstream, making the Lower Brazos River Basin an ideal study area. DIC isotopes may give two different types of information on groundwater-river exchange, depending on the rivers rate of CO2 evasion. If the river is highly supersaturated with respect to CO2 (like warm tropical rivers), the groundwater CO2 signal will be lost rapidly, creating a tracer which can detect regions of groundwater entry. If the river is weakly supersaturated (like cooler temperate rivers), the groundwater CO2 signal will persist longer distances, acting as a large-scale tracer of aquifer-river exchange processes. I propose to measure the 14C and 3C of riverine DIC and groundwater DIC to understand the systematics of the dual 14C/3C isotopic groundwater tracer in the Lower Brazos River System.