Groundwater‐derived DIC and carbonate buffering enhance fluvial CO2 evasion in two Australian tropical rivers

Duvert, Clément, Bossa, Mylène, Tyler, Kyle J., Wynn, Jonathan G., Munksgaard, Niels C., Bird, Michael I., Setterfield, Samantha A., and Hutley, Lindsay B. (2019) Groundwater‐derived DIC and carbonate buffering enhance fluvial CO2 evasion in two Australian tropical rivers. Journal of Geophysical Research: Biogeosciences, 124 (2). pp. 312-327.

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Abstract

Despite recent evidence suggesting that groundwater inputs of dissolved inorganic carbon (DIC) to rivers can contribute substantially to the fluvial evasion of carbon dioxide (CO2), groundwater is seldom integrated into fluvial carbon budgets. Also, unclear is the way equilibria between CO2 and ionic forms of carbonate will affect CO2 evasion from rivers. We conducted longitudinal river surveys of radon and carbon along two rivers of tropical Australia and developed a mass balance framework to assess the influence of groundwater‐derived inorganic carbon and carbonate buffering on CO2 evasion rates. The mean CO2 evasion flux totaled 8.5 and 2.3 g·C·m−2·day−1 for the two rivers, with considerable spatial variations that we attributed primarily to changes in groundwater inflow rates (minima and maxima per river reach 1.2–45.1 and 0.2–13.4 g·C·m−2·day−1). In the larger river system, inflowing groundwater delivered on average 6.7 g·C·m−2·day−1 as dissolved CO2—almost 10 times as much as the CO2 produced via river metabolism—and 21.6 g·C·m−2·day−1 as ionic forms. In both rivers, these groundwater‐derived inputs were a mixture of biogenic and geogenic carbon sources. Spatialized estimates of the carbonate buffering flux revealed that in reaches where CO2 evasion was particularly high, the carbonate system was able to maintain high CO2 concentrations by adjustment of carbonate equilibria. This process was likely triggered by high groundwater inflow rates. Our findings suggest that both groundwater inputs and carbonate equilibria need to be accounted for in fluvial carbon budgets, particularly in high‐alkalinity rivers.

Item ID: 57732
Item Type: Article (Research - C1)
ISSN: 2169-8961
Copyright Information: ©2019. American Geophysical Union. All Rights Reserved.
Funders: Australian Research Council (ARC)
Projects and Grants: ARC DP160101497
Date Deposited: 27 Mar 2019 07:35
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 50%
04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040608 Surfacewater Hydrology @ 50%
SEO Codes: 96 ENVIRONMENT > 9611 Physical and Chemical Conditions of Water > 961103 Physical and Chemical Conditions of Water in Fresh, Ground and Surface Water Environments (excl. Urban and @ 100%
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