Sources and preservation of organic matter in soils of the wetlands in the Liaohe (Liao River) Delta, North China Tian Lin a,b,⇑ , Siyuan Ye c , Chuanliang Ma b , Xigui Ding c , Hans Brix d , Hongming Yuan c , Yingjun Chen e , Zhigang Guo b a State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China b Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China c Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources of China, Qingdao 266071, China d Department of Bioscience, Aarhus University, Denmark e Key Laboratory of Coastal Zone Environmental Processes, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China article info Keywords: Organic matter Sources and preservation Biomarkers Soils Wetlands Liao River Delta abstract Total organic carbon, total nitrogen, d 13 C org , d 15 N, and aliphatic and polyaromatic hydrocarbons of fifty- five soil samples collected from the coastal wetlands of the Liaohe Delta were measured, in order to determine the sources and possible preservation of organic matter (OM). The d 15 N and d 13 C org values in the samples ranged from 3.0‰ to 9.4‰ and from 30.4‰ to 20.3‰, respectively, implying that the OM in the soils is predominantly derived from C 3 plant. The long-chain n-alkanes had a strong odd-over-even carbon number predominance, suggesting a significant contribution from waxes of higher plants. The ubiquitous presence of unresolved complex mixture, alkylated polycylic aromatic hydrocar- bons and typical biomarkers of petroleum hydrocarbons (pristane, phytane, hopanes and steranes) indi- cates that there is a contribution of petroleum hydrocarbons to the organic carbon pool in the wetland soils. P. australis-vegetated wetlands have strong potentials for the preservation of organic carbon in the wetlands. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Wetlands are well known for their high productivity and their potential to sequester carbon dioxide from the atmosphere. The decomposition rate of organic matter (OM) in wetland soils is gen- erally slow because of the anoxic wet conditions. It is estimated that 20–30% of the Earth’s soil pool of 2500 Pg of carbon is stored in wetlands (Roulet, 2000; Bridgham et al., 2006), although wet- lands comprise only about 5–8% of the terrestrial land surface (Mitsch and Gosselink, 2007). Wetlands are also a source of green- house gas emissions, especially methane (Mitsch et al., 2012). Thus, wetland ecosystems play a significant role in the global car- bon cycle and climate change. The coastal wetlands of the Liaohe (Liao River) Delta (LRD) are located in the northern Liaodong Bay of the Bohai Sea, North China (Fig. 1), and cover a geographic area of approximately 3150 km 2 . The common reed (Phragmites australis (Cav.) Trin. ex Steud.) is the dominant plant species in the delta wetlands, and the LRD reed stands are the largest in Asia and the second largest one in the world. The LRD is the leading economic center of Northeast China with an extensive industry based on the abundant oil and natural gas resources. Furthermore, the delta provides excellent conditions for the production of rice and commercial aquaculture systems. Due to the excessive population growth and the increasing de- mands for cultivable lands, more and more of the delta wetlands are being reclaimed. Large amounts of heavy oil-polluted process water from oil extraction in the Liaohe Oilfield, the third largest in China, are discharged into the Liao River in the Delta (Ji et al., 2002). Both the land reclamation for agriculture and aquaculture, and the oil extraction is likely to affect the production, transport and burial of OM in the LRD wetlands. One approach to understand sources and fate mechanisms of OM accumulated in sediments and soils is to utilize a molecular or- ganic geochemical method, where n-alkanes, pristane (Pr), phytane (Ph), the unresolved complex mixture (UCM), alkylated polycyclic aromatic hydrocarbons (PAHs), hopane and sterane are used for the source identification of the OM (Yunker et al., 2002b; Kimb- rough and Dickhut, 2006; Wang et al., 2006; Hu et al., 2009; Tolosa et al., 2009; Wang et al., 2011). These biomarkers, combined with total organic carbon (TOC), total nitrogen (TN), d 13 C org and d 15 N in 0025-326X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2013.01.036 ⇑ Corresponding author at: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China. Tel./fax: +86 851 5895239. E-mail address: lintian@gyig.ac.cn (T. Lin). Marine Pollution Bulletin xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Please cite this article in press as: Lin, T., et al. Sources and preservation of organic matter in soils of the wetlands in the Liaohe (Liao River) Delta, North China. Mar. Pollut. Bull. (2013), http://dx.doi.org/10.1016/j.marpolbul.2013.01.036