Air-Water CO2 Exchange in the Mountain Streams and Estuary of Kailua, Oahu, Hawaii

Abstract

Models and observational data show that the worldwide estuarine zone is likely a source of CO2, to the atmosphere but few estuarine zones around the world have been studied in detail. The mountain streams, marsh, and estuarine zone of Kailua, Oahu, Hawaii are known to be a source of CO2 to the atmosphere during dry periods, but the air-water CO2 exchange during storm events is unknown. To determine the air-water exchange during storm events, in-situ measurements of salinity, temperature, and pH were taken from 16 sites in the Kailua watershed/estuary system during 2006-2007. Only one storm event occurred during the period of the study. Water samples were also taken from each site for determination of total alkalinity and nutrient concentrations. Using salinity, temperature, pH, and total alkalinity data, the partial pressure of CO2 was calculated for 54 water samples. The average background CO2 and standard deviation for the mountain streams was 1727 ± 1399 atm and the average CO2 dropped to 702 ± 62 atm during the storm event. The background average CO2 for the marsh was 6160 ± 8245 atm and the CO2 dropped to 4809 atm during the storm event. The background average CO2 for the estuarine zone was 1790 ± 2188 atm and the average CO2 increased to 2831 ± 1561 atm during the storm event. The mouth of the concrete canal draining Kawai Nui Marsh was normally a sink for atmospheric CO2 with an average background CO2 of 265 ± 110 atm. However during the one storm event, the CO2 increased to 1728 atm at the mouth of the canal, switching to a source of CO2 to the atmosphere. During storm events, the Kailua system becomes a weaker source of atmospheric CO2.