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The role of porewater exchange as a driver of CO2 flux to the atmosphere in a temperate estuary (Squamish, Canada)

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Abstract

Porewater exchange is an important yet poorly understood component of the coastal carbon cycle. Here, a high-resolution automated radon (222Rn, a natural porewater tracer) and CO2 time series was conducted in the Squamish Central Estuary (Canada) over eight consecutive tidal cycles to assess the relative importance of porewater exchange on estuarine carbon dynamics. Radon and CO2 observations revealed a clear tidal trend which is indicative of porewater exchange driven by tidal pumping. A radon mass balance indicated an average porewater exchange rate of 14.9 cm day−1 (4.3% of the tidal prism). The estuary was a net source of CO2 to the atmosphere (average 212 ± 19 mmol m−2 day−1). Porewater exchange accounted for 9%, 5% and 30% of net dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and CO2 exported out of the Squamish Central Estuary, respectively, while porewater inputs of free CO2 accounted for 38% of the atmospheric evasion. These flux estimates as well as strong correlations between pCO2 and 222Rn suggest that porewater exchange has a strong influence on CO2 concentrations in the estuary even though they are a small contributor to overall DIC fluxes.

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Acknowledgements

We would like to thank Edith Trobe from the River Watershed Society for providing background on the estuary and input into the study design. Ceylena Holloway from NMSC provided equipment logistics and laboratory analysis. We acknowledge funding from the Australian Research Council (DE140101733, DE1500100581 and LE120100156) for analytical instrumentation and field investigations support. DRT also received support through an Australian Research Council DECRA Fellowship (DE180100535) during the data analysis and writing of the manuscript. The original data can be obtained from DRT.

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Authors and Affiliations

  1. National Marine Science Centre, Southern Cross University, PO Box 4321, Coffs Harbour, NSW, 2450, Australia

    Rowena M. Diggle, Douglas R. Tait, Damien T. Maher & Isaac R. Santos

  2. Southern Cross Geoscience, Southern Cross University, Lismore, NSW, 2480, Australia

    Douglas R. Tait & Damien T. Maher

  3. School of Engineering, University of Guelph, Guelph, ON, N1G 2W1, Canada

    Xander Huggins

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  1. Rowena M. Diggle
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Correspondence to Douglas R. Tait.

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Diggle, R.M., Tait, D.R., Maher, D.T. et al. The role of porewater exchange as a driver of CO2 flux to the atmosphere in a temperate estuary (Squamish, Canada). Environ Earth Sci 78, 336 (2019). https://doi.org/10.1007/s12665-019-8291-3

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