Oral Presentation Society for Freshwater Science 2025 Annual Meeting

Australian riverine land-to-ocean carbon export constrained by large-scale monitoring data (117074)

Francesco Ulloa Cedamanos 1 , Anna Lintern 2 , Adam Rexroade 1 , Yihan Li 1 , Dylan Irvine 1 , Marcus Wallin 3 , David Butman 4 , Lindsay Hutley 1 , Clément Duvert 1
  1. Research Institute for the Environment and Livelihoods, Charles Darwin University, Ellengowan Dr., NT, Australia
  2. Department of Civil Engineering, Monash University, Clayton, VIC, Australia
  3. Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
  4. School of Environmental and Forest Sciences, University of Washington, Seattle, WA, USA

Rivers play a crucial role in the lateral transfer, transport, and transformation of carbon (C). However, sparse observations of riverine C in Australia hinder accurate national estimates of the riverine land-to-ocean C flux, particularly for small headwater streams. To better understand the magnitude and fate of dissolved C exports, we compiled 40,986 dissolved inorganic C (DIC, mean = 12.9 ± 10.3 mg/L) and 19,177 dissolved organic C (DOC, mean = 8.8 ± 11.8 mg/L) observations and combined these data with monthly river flow data to estimate annual nationwide dissolved C export.

Our estimated annual DIC fluxes aligned with previous estimates for Australia1, while DOC fluxes were 27% higher. Additionally, we explored the spatial and seasonal patterns and drivers of dissolved C export. Overall, DOC concentrations remain stable with increasing stream order, contrasting with DIC concentrations, which increase. We also found that C export is largely transport-limited rather than source-limited, with the majority of the export occurring during the wettest months of the year and in wetter regions. Tropical drainage divisions (i.e., Tanami-Timor Sea Coast and Carpentaria Coast) accounted for 49% and 43% of the national DIC and DOC export, respectively, despite covering only 28% of the country. Within the tropics, the DIC and DOC fluxes in the wet season were up to 5,000 times higher compared to those in the dry season, largely driven by seasonal changes in flow regime. Carbonate rocks likely contributed significantly to the higher DIC export in tropical regions compared to other climatic zones, highlighting the importance of different C sources to the riverine land-to-ocean C flux.

This study underscores the variability of dissolved C in Australian rivers and emphasises the critical role of hydrological conditions and C sources in shaping the spatial and temporal patterns of riverine C.

  1. Villalobos, Y., Canadell, J.G., Keller, E.D., Briggs, P.R., Bukosa, B., Giltrap, D.L., Harman, I., Hilton, T.W., Kirschbaum, M.U.F., Lauerwald, R., Liang, L.L., Maavara, T., Mikaloff-Fletcher, S.E., Rayner, P.J., Resplandy, L., Rosentreter, J., Metz, E.M., Serrano, O., Smith, B., 2023. A Comprehensive Assessment of Anthropogenic and Natural Sources and Sinks of Australasia’s Carbon Budget. Global Biogeochem Cycles 37. https://doi.org/10.1029/2023GB007845