Browsing by Author "Santos, IR"
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- ItemAre mangrove carbon exports old or modern? A multiple radio- and stable isotope analysis(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-09) Maher, DT; Call, M; Santos, IR; Sanders, CJ; Schulz, KG; Jenkinson, A; Jacobsen, GENot provided to ANSTO Library.
- ItemBlue carbon oxidation revealed by radiogenic and stable isotopes in a mangrove system(American Geophysical Union, 2017-05-8) Maher, DT; Santos, IR; Schulz, KG; Call, M; Jacobsen, GE; Sanders, CJMangroves are among the most carbon-rich ecosystems on Earth and can sequester carbon in sediments over long timescales. Here we assess whether century-old buried carbon may be remineralized and exported by measuring Δ14C in the exported dissolved inorganic carbon (DIC) as well as sediment Δ14C profiles in a subtropical mangrove. Pore water exchange released isotopically depleted, old DIC to surface waters. Keeling plots revealed that the source of DIC to surface waters had a δ13C-DIC value of −29.4 ±1.9‰ and Δ14C-DIC value of −73±9‰. The respired and exported carbon comes from an average depth of ~40 cm, equivalent to ~100 years of sediment accumulation. Therefore, century-old sequestered carbon is still susceptible to remineralization and tidal export to the coastal ocean via pore water exchange or submarine groundwater discharge. We suggest that the timescales over which blue carbon burial is assessed should consider carbon losses via pore water exchange. © 2017. American Geophysical Union
- ItemChanges in global groundwater organic carbon driven by climate change and urbanization(Springer Nature, 2020-03-09) McDonough, LK; Santos, IR; Andersen, MS; O'Carroll, DM; Rutlidge, H; Meredith, KT; Oudone, PP; Bridgeman, J; Gooddy, DC; Sorensen, JPR; Lapworth, DJ; MacDonald, AM; Ward, J; Baker, AAClimate change and urbanization can increase pressures on groundwater resources, but little is known about how groundwater quality will change. Here, we use a global synthesis (n = 9,404) to reveal the drivers of dissolved organic carbon (DOC), which is an important component of water chemistry and substrate for microorganisms that control biogeochemical reactions. Dissolved inorganic chemistry, local climate and land use explained ~ 31% of observed variability in groundwater DOC, whilst aquifer age explained an additional 16%. We identify a 19% increase in DOC associated with urban land cover. We predict major groundwater DOC increases following changes in precipitation and temperature in key areas relying on groundwater. Climate change and conversion of natural or agricultural areas to urban areas will decrease groundwater quality and increase water treatment costs, compounding existing constraints on groundwater resources. © 2020, The Author(s)
- ItemA new conceptual framework for the transformation of groundwater dissolved organic matter(Springer Nature Limited, 2022-04-20) McDonough, LK; Andersen, MS; Behnke, MI; Rutlidge, H; Oudone, PP; Meredith, KT; O'Carroll, DM; Santos, IR; Marjo, CE; Spencer, RGM; McKenna, AM; Baker, AAGroundwater comprises 95% of the liquid fresh water on Earth and contains a diverse mix of dissolved organic matter (DOM) molecules which play a significant role in the global carbon cycle. Currently, the storage times and degradation pathways of groundwater DOM are unclear, preventing an accurate estimate of groundwater carbon sources and sinks for global carbon budgets. Here we reveal the transformations of DOM in aging groundwater using ultra-high resolution mass spectrometry combined with radiocarbon dating. Long-term anoxia and a lack of photodegradation leads to the removal of oxidised DOM and a build-up of both reduced photodegradable formulae and aerobically biolabile formulae with a strong microbial signal. This contrasts with the degradation pathway of DOM in oxic marine, river, and lake systems. Our findings suggest that processes such as groundwater extraction and subterranean groundwater discharge to oceans could result in up to 13 Tg of highly photolabile and aerobically biolabile groundwater dissolved organic carbon released to surface environments per year, where it can be rapidly degraded. These findings highlight the importance of considering groundwater DOM in global carbon budgets. © The Authors, Open Access under CC 4.0
- ItemA new conceptual framework for the transformation of groundwater dissolved organic matter(Springer Nature, 2022-04-20) McDonough, LK; Andersen, MS; Behnke, MI; Rutlidge, H; Oudone, PP; Meredith, KT; O'Carroll, DM; Santos, IR; Marjo, CE; Spencer, RGM; McKenna, AM; Baker, AAGroundwater comprises 95% of the liquid fresh water on Earth and contains a diverse mix of dissolved organic matter (DOM) molecules which play a significant role in the global carbon cycle. Currently, the storage times and degradation pathways of groundwater DOM are unclear, preventing an accurate estimate of groundwater carbon sources and sinks for global carbon budgets. Here we reveal the transformations of DOM in aging groundwater using ultra-high resolution mass spectrometry combined with radiocarbon dating. Long-term anoxia and a lack of photodegradation leads to the removal of oxidised DOM and a build-up of both reduced photodegradable formulae and aerobically biolabile formulae with a strong microbial signal. This contrasts with the degradation pathway of DOM in oxic marine, river, and lake systems. Our findings suggest that processes such as groundwater extraction and subterranean groundwater discharge to oceans could result in up to 13 Tg of highly photolabile and aerobically biolabile groundwater dissolved organic carbon released to surface environments per year, where it can be rapidly degraded. These findings highlight the importance of considering groundwater DOM in global carbon budgets. Crown Copyright © 2022
- ItemReconstructing extreme climatic and geochemical conditions during the largest natural mangrove dieback on record(European Geosciences Union (EGU), 2020-02-28) Sippo, JZ; Santos, IR; Sanders, CJ; Gadd, PS; Hua, Q; Lovelock, CE; Santini, NS; Johnston, SG; Harada, Y; Reithmeir, G; Maher, DTA massive mangrove dieback event occurred in 2015–2016 along ∼ 1000 km of pristine coastline in the Gulf of Carpentaria, Australia. Here, we use sediment and wood chronologies to gain insights into geochemical and climatic changes related to this dieback. The unique combination of low rainfall and low sea level observed during the dieback event had been unprecedented in the preceding 3 decades. A combination of iron (Fe) chronologies in wood and sediment, wood density and estimates of mangrove water use efficiency all imply lower water availability within the dead mangrove forest. Wood and sediment chronologies suggest a rapid, large mobilization of sedimentary Fe, which is consistent with redox transitions promoted by changes in soil moisture content. Elemental analysis of wood cross sections revealed a 30- to 90-fold increase in Fe concentrations in dead mangroves just prior to their mortality. Mangrove wood uptake of Fe during the dieback is consistent with large apparent losses of Fe from sediments, which potentially caused an outwelling of Fe to the ocean. Although Fe toxicity may also have played a role in the dieback, this possibility requires further study. We suggest that differences in wood and sedimentary Fe between living and dead forest areas reflect sediment redox transitions that are, in turn, associated with regional variability in groundwater flows. Overall, our observations provide multiple lines of evidence that the forest dieback was driven by low water availability coinciding with a strong El Niño–Southern Oscillation (ENSO) event and was associated with climate change. © Author(s) 2020.
- ItemUsing radiocarbon and organic carbon characterisation techniques to identify the sources and degradation of dissolved organic matter in groundwater(Australian Nuclear Science and Technology Organisation, 2021-11-17) McDonough, LK; Meredith, KT; Rutlidge, H; Andersen, MS; O'Carroll, DM; Oudone, PP; Behke, MI; Marjo, CE; Santos, IR; Spencer, RG; McKenna, A; Baker, AADissolved organic matter (DOM) plays a significant role in biogeochemical processes, ecological functioning, and carbon cycling. Interactions with the environment over time results in changes to the molecular size of DOM molecules as well as the number and arrangement of their atoms, thereby changing DOM reactivity, functioning and fate. Significant advances have been made in our understanding of surface water DOM sources and degradation throughout the past decade, largely due to the development of ultra-high resolution carbon characterisation techniques such as Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) which can be linked to changes in radiocarbon (¹⁴ C) dissolved organic carbon (DOC) content. The sources and degradation of DOM in groundwater, however, remains poorly studied. This is in part due to the typically low (~1 ppm) DOM concentrations in these environments, meaning that in the past, large quantities of water were required for ¹⁴ C-DOC analyses. The ability to measure ¹⁴ C in small mass samples on ANTARES allows for a larger throughput of ¹⁴ C-DOC samples and quicker sample preparation due to lower quantities of water required. Here, we combine ¹⁴ C-DOC, ¹⁴ C of dissolved inorganic carbon (DIC), FT-ICR MS, liquid chromatography organic carbon detection, fluorescence and DOC concentrations to identify groundwater DOM sources at three locations in New South Wales. We then determine the changes in DOM character as it ages in groundwater. Sources identified include aged peat with an aromatic character and a young hydrophilic terrestrial source. The young terrestrial source was found to degrade into carboxylic-rich alicyclic molecules with intermediate hydrogen/carbon (H/C) and low to intermediate oxygen/carbon (O/C) ratios in shallow groundwater. In contrast, increasing thermodynamic constraints in deep confined aquifers resulted in an increase in ancient (up to 25,310 ± 600 years before present) low O/C DOM due to the preferential microbial decomposition of more oxidised formulae. We also identify the accumulation of high H/C and heteroatom containing microbial metabolites and biomass in deep highly aged anoxic groundwater. Our results show that the current paradigm of aged, stable DOM occurring in the centre of H/C versus O/C space may be constrained to well-mixed, oxic aquatic environments. In contrast, the oldest DOM appears instead to occur in anoxic aquifers where the most persistent formulae have high H/C and low O/C ratios. Interestingly, these formulae are typically biolabile in aerobic environments.