QI Di¹, ZHAI Wei-dong^{2, *}, CHEN Neng-wang¹, WU Jie-zhong¹

 (1. College of Environment and Ecology, Xiamen University, Xiamen 361102, China; 2. National Marine Environmental Monitoring Center, Dalian 116023, China) 

Abstract: The authors investigated the distributions of surface water dissolved oxygen (DO), pH, dissolved inorganic carbon (DIC) and total alkalinity (TAlk) and calculated the partial pressure of CO₂ (pCO₂) in the Jiulongjiang River, a subtropical river in Fujian Province, China. The average values of DO% and pH were 67±18% and 7.08±0.12 in the dry season, and 57±12% and 7.22±0.11 in the flood season. The lowest values of DO% and pH were 10% and 6.88 in the dry season, and 35% and 6.98 in the flood season. The average DIC was 1027±620 µmol/kg in the dry season and 820±340 µmol/kg in the flood season. TAlk was 885±570 µmol/kg in the dry season. TAlk was mainly controlled by the geological background and chemical weathering in the watershed. However, most of free CO₂ was associated with aerobic respiration in water columns and anaerobic processes in the sediments. Aqueous pCO₂ in the Jiulongjiang River was  3470±1640 µatm on average in the dry season and 3590±1410 µatm on average in the wet season, respectively. Based on data analyses between supersaturated CO₂ and apparent oxygen utilization, it was concluded that the in-situ aerobic respiration accounts for 66-94% of the supersaturated CO₂ in the Jiulongjiang River, and the remaining supersaturated CO₂ may come from denitrification in the sediments.

Key words: riverine pCO₂; carbonate system; respiration; Jiulongjiang River

EARTH AND ENVIRONMENT Vol. 42, No.3, Tot No.299, 2014, Page 286-296