Alkalinity and dissolved inorganic carbon exports from tropical and subtropical river catchments discharging to the Great Barrier Reef, Australia

Abstract

Dissolved inorganic carbon (DIC) transport by rivers is an important control on the pH and carbonate chemistry of the coastal ocean. Here, we combine DIC and total alkalinity (TAlk) concentrations from four tropical rivers of the Great Barrier Reef region in Australia with daily river discharge to quantify annual river loads and export rates. DIC in the four rivers ranged from 284 to 2,639 μmol kg−1 and TAlk ranged from 220 to 2,612 μmol kg−1. DIC:TAlk ratios were mostly greater than one suggesting elevated exports of free [CO2*]. This was pronounced in the Johnstone and Herbert rivers of the tropical wet north. The largest annual loads were transported in the two large river catchments of the southern Great Barrier Reef region, the Fitzroy and Burdekin rivers. The carbon stable isotopic composition of DIC suggests that carbonate weathering was the dominant source of DIC in the southern rivers, and silicate weathering was likely a source of DIC in the northern Wet Tropics rivers. Annual loads and export rates were strongly driven by precipitation and discharge patterns, the occurrence of tropical cyclones, and associated flooding events, as well as distinct seasonal dry and wet periods. As such, short‐lived hydrological events and long‐term (seasonal and inter‐annual) variation of DIC and TAlk that are pronounced in rivers of the tropical and subtropical wet and dry climate zone should be accounted for when assessing inorganic carbon loads to the coastal ocean and the potential to buffer against or accelerate ocean acidification.

Progressive seawater acidification on the Great Barrier Reef continental shelf

“…However, at this site macronutrient availability did not appear to be a dominant driver of the CO 2 variation on seasonal scales. Overall, concentrations of alkalinity and DIC appear typically lower in Burdekin River discharge waters than in seawater, but they are higher in alkalinity than in DIC 50 . Due to the sparsity of relevant river data and complex hydrodynamics, it remains unclear to what extent rivers affect the alkalinity and inorganic carbon concentrations of GBR ecosystems, either directly through their DIC, alkalinity and nutrient loads, or indirectly via stimulation of biological processes.…”

A Modeling Approach for Addressing Sensitivity and Uncertainty of Estuarine Greenhouse Gas (CO2 and CH4) Dynamics

“…The initial concentrations of DIC and CH 4 in the riverine inflows and WWTP discharges were first constrained based on the literature values and then integrated into the PEST for optimization and uncertainty analysis. Riverine DIC concentrations and inflow rates commonly follow power law trends (Rosentreter & Eyre, 2020; Tanner & Eyre, 2020). This trend was applied in this study with average DIC concentration measured during the two field campaigns and riverine inflow rates in the Brisbane River Estuary.…”

Dissolved inorganic carbon isotopes of a typical alpine river on the Tibetan Plateau revealing carbon sources, wetland effect and river recharge

“…The weathering of carbonates and silicates is a significant process of DIC input into riverine systems (Rosentreter & Eyre, 2020;Telmer & Veizer, 1999). In the Nyangqu River, the DIC derived from the weathering of carbonate minerals can be achieved by both sulphuric acid (Equation 3) and carbonic acid (Equation 4), as well as silicate weathering by carbonic acid (Equation 5).…”

“…Riverine DIC has three main sources with distinct isotopic signatures, including soil CO 2 , dissolution of carbonate minerals and atmospheric CO 2 (Aucour et al, 1999;Yang et al, 1996). Therefore, the mixture of different carbon sources, as well as biogeochemical processes, can lead to the variations of δ 13 C DIC values in rivers (Amiotte-Suchet et al, 1999;Atkins et al, 2013;Cameron et al, 1995;Liu et al, 2020;Rosentreter & Eyre, 2020;Yang et al, 1996) and groundwater (Jiráková et al, 2010;Porowska, 2015).…”