, Volume 100, Issue 1-3, pp 211-225

Sources of CO2 evasion from two subtropical rivers in North America

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Abstract

We directly measured the partial pressure of dissolved CO2 (pCO2) in two humid subtropical rivers in coastal Texas, one highly urbanized (Buffalo Bayou) and one relatively undeveloped (Spring Creek), and analyzed carbon isotopic signatures (Δ14C and δ 13C) of riverine dissolved inorganic carbon (DIC) to determine carbon sources sustaining river respiration. Both rivers were highly supersaturated with CO2 at all study sites and on all dates sampled from June 2007 to February 2009. Mean riverine pCO2 values are 3,052 ± 1,364 and 4,702 ± 1,980 μatm for Buffalo Bayou and Spring Creek, respectively. Calculated CO2 emission fluxes per ha of water surface area from these rivers are intermediate between those in tropical and temperate rivers, indicating that globally, humid subtropical rivers may be a significant source of atmospheric CO2. Carbon isotopic signatures revealed that CO2 supersaturation is supported by different carbon sources for the two rivers. In the relatively undeveloped river (Spring Creek), young terrestrial organic matter (OM) is the predominant C source fueling river heterotrophic respiration. In the highly urbanized river (Buffalo Bayou), the high concentration of riverine CO2 is additionally supported by dissolution of CaCO3 likely from pedogenic carbonate, and crushed limestone/dolomite and oyster shells imbedded in old roads in the watershed. Because urban sources of acidity can include HNO3 and H2SO4, whether the limestone/dolomite and shells used by humans act as a net sink or source of atmospheric CO2 needs further study.