Portal de Periódicos da CAPES

Groundwater‐Derived DIC and Carbonate Buffering Enhance Fluvial CO 2 Evasion in Two Australian Tropical Rivers

2019; Wiley; Volume: 124; Issue: 2 Linguagem: Inglês

10.1029/2018jg004912

2169-8961

Clément Duvert, Mylène Bossa, Kyle J. Tyler, Jonathan G. Wynn, Niels C. Munksgaard, Michael I. Bird, Samantha A. Setterfield, Lindsay B. Hutley,

Atmospheric and Environmental Gas Dynamics

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 (CO 2 ), groundwater is seldom integrated into fluvial carbon budgets. Also, unclear is the way equilibria between CO 2 and ionic forms of carbonate will affect CO 2 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 CO 2 evasion rates. The mean CO 2 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 CO 2 —almost 10 times as much as the CO 2 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 CO 2 evasion was particularly high, the carbonate system was able to maintain high CO 2 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.