Browsing by Author "Duvert, C"
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- ItemExtreme 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, MIIn 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.
- ItemHydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivity(Elsevier, 2015-10-01) Duvert, C; Raiber, M; Owen, DDR; Cendón, DI; Batiot-Guilhe, C; Cox, MEIn areas of potential coal seam gas (CSG) development, understanding interactions between coal-bearing strata and adjacent aquifers and streams is of highest importance, particularly where CSG formations occur at shallow depth. This study tests a combination of hydrochemical and isotopic tracers to investigate the transient nature of hydrochemical processes, inter-aquifer mixing and recharge in a catchment where the coal-bearing aquifer is in direct contact with the alluvial aquifer and surface drainage network. A strong connection was observed between the main stream and underlying alluvium, marked by a similar evolution from fresh Ca–Mg–HCO3 waters in the headwaters towards brackish Ca–Na–Cl composition near the outlet of the catchment, driven by evaporation and transpiration. In the coal-bearing aquifer, by contrast, considerable site-to-site variations were observed, although waters generally had a Na–HCO3–Cl facies and high residual alkalinity values. Increased salinity was controlled by several coexisting processes, including transpiration by plants, mineral weathering and possibly degradation of coal organic matter. Longer residence times and relatively enriched carbon isotopic signatures of the downstream alluvial waters were suggestive of potential interactions with the shallow coal-bearing aquifer. The examination of temporal variations in deuterium excess enabled detection of rapid recharge of the coal-bearing aquifer through highly fractured igneous rocks, particularly at the catchment margins. Most waters collected from the coal-bearing aquifer also showed an enhanced influence of weathering during the wet season, which was likely triggered by the water–rock interaction with fresh recharge waters. An increase in both residual alkalinity and carbon isotopic ratios at two locations indicated inter-aquifer mixing between alluvium and bedrock during the wet season. The results of this study emphasise the need for conducting baseline hydrochemical surveys prior to CSG development in order to describe the transient nature of recharge and inter-aquifer mixing processes. © 2015, Elsevier Ltd.
- ItemSeasonal and spatial variations in rare elements to identify inter-aquifer linkages and recharge processes in an Australian catchment(Elsevier B. V., 2015-03-09) Duvert, C; Cendón, DI; Raiber, M; Seidel, JL; Cox, MEWith the aim of elucidating the seasonal behaviour of rare earth elements (REEs), surface and groundwaters were collected under dry and wet conditions in different hydrological units of the Teviot Brook catchment (Southeast Queensland, Australia). Sampled waters showed a large degree of variability in both REE abundance and normalised patterns. Overall REE abundance ranged over nearly three orders of magnitude, and was consistently lower in the sedimentary bedrock aquifer (18ppt<∑REE<477ppt) than in the other hydrological systems studied. Abundance was greater in springs draining rhyolitic rocks (∑REE=300 and 2054ppt) than in springs draining basalt ranges (∑REE=25 and 83ppt), yet was highly variable in the shallow alluvial groundwater (16ppt<∑REE<5294ppt) and, to a lesser extent, in streamwater (85ppt<∑REE<2198ppt). Generally, waters that interacted with different rock types had different REE patterns. In order to obtain an unbiased characterisation of REE patterns, the ratios between light and middle REEs (R(M/L)) and the ratios between middle and heavy REEs (R(H/M)) were calculated for each sample. The sedimentary bedrock aquifer waters had highly evolved patterns depleted in light REEs and enriched in middle and heavy REEs (0.17
- ItemSeasonal 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, MIThe 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
- ItemSeasonal wetlands make a relatively limited contribution to the dissolved carbon pool of a lowland headwater tropical stream(American Geophysical Union (AGU), 2024-02-07) Solano, V; Duvert, C; Hutley, LB; Cendón, DI; Maher, DT; Birkel, CWetlands process large amounts of carbon (C) that can be exported laterally to streams and rivers. However, our understanding of wetland inputs to streams remains unclear, particularly in tropical systems. Here we estimated the contribution of seasonal wetlands to the C pool of a lowland headwater stream in the Australian tropics. We measured dissolved organic and inorganic C (DOC and DIC) and dissolved gases (carbon dioxide—CO2, methane—CH4) during the wet season along the mainstem and in wetland drains connected to the stream. We also recorded hourly measurements of dissolved CO2 along a ‘stream–wetland drain–stream’ continuum, and used a hydrological model combined with a simple mass balance approach to assess the water, DIC and DOC sources to the stream. Seasonal wetlands contributed ∼15% and ∼16% of the DOC and DIC loads during our synoptic sampling, slightly higher than the percent area (∼9%) they occupy in the catchment. The riparian forest (75% of the DOC load) and groundwater inflows (58% of the DIC load) were identified as the main sources of stream DOC and DIC. Seasonal wetlands also contributed marginally to stream CO2 and CH4. Importantly, the rates of stream CO2 emission (1.86 g C s−1) and DOC mineralization (0.33 g C s−1) were much lower than the downstream export of DIC (6.39 g C s−1) and DOC (2.66 g g C s−1). This work highlights the need for further research on the role of riparian corridors as producers and conduits of terrestrial C to tropical streams. © 2024. The Authors. This is an open access article under the terms of the Creative Commons Attribution License.
- ItemTime-series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream(Hydrological Earth Systems Sciences, 2016-01-18) Duvert, C; Stewart, MK; Cendón, DI; Raiber, MA major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics. In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT ≈ 2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT ≈ 0.3 years). The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best fits between measured and modelled tritium activities were obtained for a mean TT of 16–25 years for this older groundwater component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream ( ≈ 76–102 years), emphasising the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values averaging 17 ± 6 years at low flow and 38 ± 15 years after major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly understood. © Author(s) 2016. CC Attribution 3.0 License.