Stable Carbon Isotope and Long-Chain Alkane Compositions of the Major Plants and Sediment Organic Matter in the Yellow River Estuarine Wetlands

Elemental (TOC, TN, C/N) and stable carbon isotopic (C-13) compositions and long-chain alkane (nC(16-38)) concentrations were measured for eight major plants and a sediment core collected from the Yellow River estuarine wetlands. Our results indicate that both C-3 (-25.4 parts per thousand to -29.6 parts per thousand) and C-4 (-14.2 parts per thousand to -15.0 parts per thousand) plants are growing in the wetlands and C-3 plants are the predominant species. The biomass of the wetland plants had similar organic carbon (35.5-45.8%) but very different organic nitrogen (0.35-4.15%) contents. Both C-3 and C-4 plants all contained long-chain alkanes with strong odd-to-even carbon numbered chain predominance. Phragmites australis, a dominant C-3 plant contained mainly nC(29) and nC(31) homologues. Aeluropus littoralis, an abundant C-4 plant were concentrated with nC(27) and nC(29) homologues. Organic matter preserved in the Yellow River estuarine sediments showed strong terrestrial signals (C/N = 11-16, C-13 = -22.0 parts per thousand to -24.3 parts per thousand). The distribution of long-chain n-alkanes in sediments also showed strong odd-to-even carbon chain predominance with nC(29) and nC(31) being the most abundant homologues. These results suggest that organic matter preserved in the Yellow River estuarine sediments were influenced by the wetland-derived organic matter, mainly C-3 plants. The Yellow River estuarine wetland plants could play important role affecting both the carbon and nutrient cycling in the estuary and adjacent coastal waters.