State Water Resources Research Institute Program

Project ID: 2007TX269B
Title: Carbon isotopic measurements of dissolved inorganic carbon: A new tool to assess groundwater-river exchange in the Brazos River Basin
Project Type: Research
Start Date: 3/01/2007
End Date: 2/29/2008
Congressional District: 31, 17, 10, 22, 14
Focus Categories: Groundwater, Surface Water, Water Use
Keywords: groundwater, groundwater-river exchange, radiocarbon, carbon isotopic composition, dissolved inorganic carbon
Principal Investigators: Zeng, Fenwei; Masiello, Caroline A
Federal Funds: $ 5,000
Non-Federal Matching Funds: $ 10,000
Abstract: The isotopic composition (Δ14C and δ13C) 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 Δ14C and δ13C of river water sources are significantly different (groundwater: δ13Δ14C∝-5000/00, C∝-100/00; surface runoff: Δ14C∝+600/00, δ13C∝-150/00), 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 river's 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 Δ14C and δ13C of riverine DIC and groundwater DIC to understand the systematics of the dual Δ14C/δ13C isotopic groundwater tracer in the Lower Brazos River System.

Progress/Completion Report, PDF

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