Carbon dioxide dynamics in rivers and coastal waters of the “big island” of Hawaii,USA, during baseline and heavy rain conditions

The distributions of the partial pressure of carbon dioxide (pCO₂) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed an oversaturation in CO₂ with respect to atmospheric equilibrium and a CO₂ undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO₂ values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO₂ from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are the predominant drivers of the spatial and temporal patterns in the distribution of pCO₂. In Hilo Bay, CO₂ oversaturation dominates and the bay was a source of CO₂ to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the bay is not a significant source of CO₂ to the atmosphere.