Diel variability of pCO 2 and CO 2 outgassing from the lower Mississippi River: Implications for riverine CO 2 outgassing estimation

Authors

Jeremy H. Reiman, LSU Agricultural Center
Y. Jun Xu, LSU Agricultural Center

Document Type

Article

Publication Date

12-27-2018

Abstract

Carbon dioxide (CO 2 ) outgassing from river surface waters is an important component of the global carbon cycle currently not well constrained. To test the hypothesis that riverine partial pressure of CO 2 (pCO 2 ) and CO 2 outgassing rates differ between daylight and darkness, we conducted in-situ pCO 2 and ambient water measurements over four 24-h periods in the spring and summer of 2018 in the Lower Mississippi River under varying flow regimes. We hypothesized that diel pCO 2 variation will correlate inversely with solar radiation due to light-induced photosynthesis. Despite differing ambient conditions between seasons, we found a consistent diel cycle of riverine pCO 2 , with highest values before sunset and lowest values during peak daylight. Recorded pCO 2 measurements varied by 206-607 μatm in spring and 344-377 μatm in summer, with significantly lower records during daylight in summer. CO 2 outgassing was significantly lower during daylight in both seasons, with diel variation ranging between 1.5-4.4 mmol m -2 h -1 in spring and 1.9-2.1 mmol m -2 h -1 in summer. Daily outgassing rates calculated incorporating diel variation resulted in significantly greater rates (26.2 ± std. 12.7 mmol m -2 d -1 ) than calculations using a single daily pCO 2 value. This study suggests a likely substantial underestimation of carbon outgassed from higher order rivers that make up a majority of the global river water surface. The findings highlight the need for high temporal resolution data and further research on diel CO 2 outgassing in different climate regions to constrain uncertainties in riverine flux estimation.

Publication Source (Journal or Book title)

Water (Switzerland)

Recommended Citation

Reiman, J., & Xu, Y. (2018). Diel variability of pCO 2 and CO 2 outgassing from the lower Mississippi River: Implications for riverine CO 2 outgassing estimation. Water (Switzerland), 11 (1) https://doi.org/10.3390/w11010043