Sources and distributions of terrigenous organic matter in a mangrove fringed small tropical estuary in South China
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Sources and distributions of terrigenous organic matter in a mangrove fringed small tropical estuary in South China BAO Hongyan1 , WU Ying1∗ , TIAN Lixin1 , ZHANG Jing1 , ZHANG Guiling2 1
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, 200062, China 2 Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China Received 19 November 2011; accepted 21 August 2012 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2013
Abstract The sources and distributions of terrigenous organic matter (OM) were investigated in a small tropical estuary in the Hainan Island, South China. Plants, suspended particulate matter (SPM), and surface sediments samples in the estuary and coast were collected. Bulk properties [organic carbon (OC%), total nitrogen (TN%), stable carbon isotope (δ13 C) and grain size] and lignin phenol concentrations were measured. OC% of mangrove plants was (43.4±2.1)%, which is similar to the values reported for mangrove plants in other regions. OC% of sediment samples ranged from 0.07% to 1.42%, and they were related to the sediment texture. Lignin phenols in the sediment ranged from 5.16 mg/100 mg OC in the uppermost station to 0.51 mg/100 mg OC in the coast. The molar ratio of organic carbon to total nitrogen (C/N) (∼7) and δ13 C (∼–31.1×10−3 ) of riverine SPM revealed that the major OM sources of riverine SPM were aquatic OM (phytoplankton and/or bacteria). Moreover, the lower lignin concentration (Λ8) and higher (Ad/Al)v of lignin phenols suggest that terrestrial OM in riverine SPM were mainly from soil. Furthermore, C/N ratio, δ13 C and lignin phenols reveal that mangrove plants were the predominant OM sources of mangrove surface sediment. Based on the δ13 C and lignin phenols, it can be concluded that the major OM sources in estuarine and coastal surface sediments were marine phytoplankton, riverine SPM and mangrove surface sediment. In addition, the higher (Ad/Al)v of lignin phenols in those coastal sediments indicate that seagrass might be a potential OM source in coastal sediments, however, the lower (Ad/Al)v in the estuarine sediments in turn suggests that seagrass could not be transported to the mangrove fringed region. A three-end-member model which is based on lignin concentrations and δ13 C was applied to evaluate the contribution of mangroves to the organic matter preserved in the surface sediments. Around the mangrove fringed region, mangrove could contribute more than 50% to the sedimentary OM, and this value is much higher than riverine OM. Nevertheless, mangrove OM could not be efficiently transported to the coastal region. Our study suggests that mangrove forest is an important OM source in this small estuary. Key words: mangrove, lignin phenols, carbon isotope, organic matter, small river Citation: Bao Hongyan, Wu Ying, Tian Lixin, Zhang Jing, Zhang Guiling. 2013. Sources and distributions of terrigenous organic matter in a mangrove fringed small tro
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