Browsing by Author "Rudge, M"

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    Extreme seasonal shifts in water and carbon sources to a wet-dry tropical river
    (Copernicus Publications, 2019-04-07) Duvert, C; Hutley, LB; Birkel, C; Rudge, M; Munksgaard, NC; Wynn, JG; Setterfield, SA; Cendón, DI; Bird, MI
    In regions with extreme climatic seasonality, the riverine export of carbon is expected to be driven by changes in connectivity between source areas and rivers. Yet we lack a thorough understanding of the relative contributions of each water source (e.g. wetlands, shallow soils, deep aquifers) to the dissolved carbon flux, and of the way these contributions vary with seasonal changes in flow regime. Here we assess the temporal variations in dissolved inorganic carbon (DIC) fluxes in a wet-dry tropical river of northern Australia, using weekly to monthly measurements of electrical conductivity, DIC and its carbon isotopic ratio ( 13CDIC), as well as the isotopes of water ( D, 18O and 3H), over a two-year period. We use linear mixing models integrated into a Bayesian framework to determine the relative contributions of stormflow, saturation areas, shallow groundwater and a deep carbonate aquifer to river fluxes, which we relate to water ages using lumped models fitted to isotopic time-series. Our results suggest extreme shifts in water and associated carbon sources between the wet and dry seasons. During the wet season, most DIC was transported by young water sources (< 1 year) originating mainly from saturation areas (52–82%) and stormflow (13–40%). This DIC was of biogenic origin (mean 13CDIC –18h). As rainfall ceased, the drainage of floodplains and wetlands occurred until all saturation areas either dried out or became disconnected from the river network. From this stage, river flow decreased substantially and the remaining DIC was nearly entirely conveyed via deeper, older water sources (20–40 years) from the underlying carbonate formation (85–95%). This DIC had a likely geogenic origin (mean 13CDIC –14h). Because of the disproportionately high flows during the wet season, the flux of DIC was larger during that period, an indication of the prevalence of biogenic carbon to the total DIC flux in this system. Our findings illustrate the need to consider dominant water flowpaths, as well as their changing patterns of connectivity, if we are to inform carbon fluxes across catchments. This work also suggests that carbon inputs to rivers need to be systematically partitioned between biogenic and geogenic sources, as this is an important consideration when evaluating the strength of soil carbon sinks. © Author(s) 2019. CC Attribution 4.0 license.
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    Seasonal shift from biogenic to geogenic fluvial carbon caused by changing water sources in the wet-dry tropics
    (American Geophysical Union, 2020-02-05) Duvert, C; Hutley, LB; Birkel, C; Rudge, M; Munksgaard, NC; Wynn, JG; Setterfield, SA; Cendón, DI; Bird, MI
    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. © 2021 American Geophysical Union