Seasonal shift from biogenic to geogenic fluvial carbon caused by changing water sources in the wet-dry tropics

Duvert, Clement, Hutley, Lindsay B., Birkel, Christian, Rudge, Mitchel, Munksgaard, Niels C., Wynn, Jonathan G., Setterfield, Samantha A., Cendon, Dioni, and Bird, Michael I. (2020) Seasonal shift from biogenic to geogenic fluvial carbon caused by changing water sources in the wet-dry tropics. Journal of Geophysical Research: Biogeosciences, 125 (2). e2019JG005384.

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Abstract

The riverine export of carbon is expected to be driven by changes in connectivity between source areas and streams. Yet we lack a thorough understanding of the relative contributions of different water sources to the dissolved carbon flux, and of the way these contributions vary with seasonal changes in flow connectivity. Here we assess the temporal variations in water and associated dissolved inorganic carbon (DIC) sources and fluxes in a wet-dry tropical river of northern Australia over two years. We use linear mixing models integrated into a Bayesian framework to determine the relative contributions of rainfall, seasonal wetlands, shallow groundwater, and a deep carbonate aquifer to riverine DIC fluxes, which we relate to the age of water sources. Our results suggest extreme shifts in water and DIC sources between the wet and dry seasons. Under wet conditions, most DIC was of biogenic origin and transported by relatively young water sources originating from shallow groundwater and wetlands. As rainfall ceased, the wetlands either dried out or became disconnected from the stream network. From this stage, DIC switched to a geogenic origin, nearly entirely conveyed via older water sources from the carbonate formation. Our findings demonstrate the importance of changing patterns of connectivity when evaluating riverine DIC export from catchments. This work also illustrates the need to systematically partition DIC fluxes between biogenic and geogenic sources, if we are to quantify how the riverine export of carbon affects net carbon soil storage.

Item ID: 63480
Item Type: Article (Research - C1)
ISSN: 2169-8961
Copyright Information: © 2020. American Geophysical Union. All Rights Reserved.
Funders: Australian Research Council (ARC), Australia's Nuclear Science and Technology Organisation (ANSTO)
Projects and Grants: ARC DP160101497, ANSTO 11066
Date Deposited: 17 Jun 2020 07:35
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 50%
04 EARTH SCIENCES > 0406 Physical Geography and Environmental Geoscience > 040603 Hydrogeology @ 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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