Photo-production of dissolved inorganic carbon from dissolved organic matter in contrasting coastal waters in the southwestern Taiwan Strait, China

• Published in: Journal of environmental sciences (China) Vol. 24; no. 7; pp. 1181 - 1188
• Main Authors: Guo, Weidong, Yang, Liyang, Yu, Xiangxiang, Zhai, Weidong, Hong, Huasheng
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.07.2012; State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China; College of Oceanography and Environmental Science, Xiamen University, Xiamen 361005, China
• Subjects: absorption; Brackish; brackish water; carbon; Carbon - analysis; Carbon Cycle; China; chromophoric dissolved organic matter; coastal water; dissolved inorganic carbon; dissolved organic matter; estuary; Fluorescence; irradiation; molecular weight; Organic Chemicals - chemistry; photo-production and -degradation; Photolysis; seawater; Seawater - analysis; Seawater - chemistry; solar radiation; Spectrophotometry, Ultraviolet; summer; 中国; 台湾海峡; 有色可溶性有机物; 沿海水域; 溶解无机碳; 照片; 物质生产; 西南部; China; ISEW, Pacific, Taiwan Strait; China, People's Rep; dissolved inorganic carbon; chromophoric dissolved organic matter; photo-production and -degradation; estuary; seawater
• ISSN: 1001-0742; 1878-7320
• DOI: 10.1016/S1001-0742(11)60921-2

Photo-production of dissolved inorganic carbon (DIC) from chromophoric dissolved organic matter (CDOM) is an important transformation process in marine carbon cycle, but little is known about this process in Chinese coastal systems. This study investigated an estuarine water sample and a coastal seawater sample from the subtropical waters in southeast of China. Water samples were exposed to natural sunlight and the absorption and fluorescence of CDOM as well as the DIC concentration were measured in the summer of 2009. The estuarine water had higher CDOM level, molecular weight and proportion of humic-like fluorescent components than the seawater that exhibited abundant tryptophan-like fluorescent component. After a 3-day irradiation, the CDOM level decreased by 45% in the estuarine water and 20% in the seawater, accompanied with a decrease in the molecular weight and aromaticity of DOM which was inferred from an increase in the absorption spectral slope parameter. The photo-degradation rates of all the five fluorescent components were also notable, in particular two humic-like components (C4 and C5) were removed by 78% and 69% in the estuarine water and by 69% and 56% in the seawater. The estuarine water had a higher photo-production rate of DIC than the seawater (4.4 vs. 2.5 μmol/(L·day)), in part due to its higher CDOM abundance. The differences in CDOM compositions between the two types of waters might be responsible for the higher susceptibility of the estuarine water to photo-degradation and hence could also affect the photo-production process of DIC.