CHARACTERISTICS OF AIR-WATER CO₂ EXCHANGE AT THE YAMATO RIVER MOUTH BY CONTINUOUS WATER QUALITY MONITORING

Abstract

 Water quality monitoring surveys were carried out for every season at the mouth of the Yamato river in order to examine the air-water CO₂ exchange characteristics in the urban estuarine area. In addition, we obtained a regression equation between the electrical conductivity (EC) and the total alkalinity (TA) based on the relationship between EC and TA of the water sampled at some points of Yamato river in order to estimate the TA required for calculation of the partial pressure of CO₂ in water (pCO₂) from the monitoring data of EC.

 The pCO_2w had large daily fluctuations in summer and fall, but the pCO_2w had small values and small daily fluctuations in winter. As a result of multiple regression analysis of pCO_2w and the observation items, the air-water CO₂ exchange depended on the change in salinity due to the tidal change and the change in pH due to the photosynthesis and the respiration. The averaged air-water CO₂ flux was 7.9 ± 0.6 CO₂/m²/hr in spring, 2.90 ± 0.7 CO₂/m²/hr in summer, 16.2 ± 1.3 CO₂/m²/hr in fall, -4.2 ± 0.5 CO₂/m²/hr in winter, and the Yamato river estuarine area acted net CO₂ sources except in winter.