The CO2 system in rivers of the Australian Victorian Alps: CO2 evasion in relation to system metabolism and rock weathering on multi-annual time scales

The patterns of dissolved inorganic C (DIC) and aqueous CO₂ in rivers and estuaries sampled during summer and winter in the Australian Victorian Alps were examined. Together with historical (1978–1990) geochemical data, this study provides, for the first time, a multi-annual coverage of the linkage between CO₂ release via wetland evasion and CO₂ consumption via combined carbonate and aluminosilicate weathering. δ¹³C values imply that carbonate weathering contributes ∼36% of the DIC in the rivers although carbonates comprise less than 5% of the study area. Baseflow/interflow flushing of respired C3 plant detritus accounts for ∼50% and atmospheric precipitation accounts for ∼14% of the DIC. The influence of in river respiration and photosynthesis on the DIC concentrations is negligible. River waters are supersaturated with CO₂ and evade ∼27.7 × 10⁶ mol/km²/a to ∼70.9 × 10⁶ mol/km²/a CO₂ to the atmosphere with the highest values in the low runoff rivers. This is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds. Evaded CO₂ is not balanced by CO₂ consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived H₂CO₃. The results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived DIC concentrations are not directly connected to high carbonate and aluminosilicate weathering rates.