Sustained high CO

Many of the world’s rivers have been found to be sources of CO2 to the atmosphere, however, there has been limited assessment in arid regions. This analysis of a long-term (1979–2013) dataset (n = 3496) along Australia’s largest river system (River Murray) showed that there were sustained high pCO2 (carbon dioxide partial pressure) levels, ranging from 1210 ± 107 to 3066 ± 579 µatm along the main river channel, and 5114 ± 1221 µatm on the major tributaries. As a consequence, the River Murray is a significant source of CO2 to the atmosphere, with an estimated average annual (±s.d.) flux of 218 ± 98 g C m−2 year−1 and total emissions of 355 000 ± 29 000 t CO2 year−1 over a total river area of 386 km2 from below Lake Hume to Tailem Bend, although there is some uncertainty with gas transfer coefficients. Supersaturation with CO2 relative to the atmosphere was maintained even under drought conditions with minimal external carbon inputs, suggesting internal carbon cycling and respiration is important in driving net CO2 production. Supersaturation of the river water relative to calcium carbonate minerals was also observed under low flow conditions. Hydro-climatic changes could be having significant impacts on the CO2 system in the River Murray and other arid river systems.