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

Abstract

Elemental (TOC, TN, C/N) and stable carbon isotopic (δ13C) compositions and long-chain alkane (nC16−38) concentrations were measured for eight major plants and a sediment core collected from the Yellow River estuarine wetlands. Our results indicate that both C3 (−25.4‰ to −29.6‰) and C4 (−14.2‰ to −15.0‰) plants are growing in the wetlands and C3 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 C3 and C4 plants all contained long-chain alkanes with strong odd-to-even carbon numbered chain predominance. Phragmites australis, a dominant C3 plant contained mainly nC29 and nC31 homologues. Aeluropus littoralis, an abundant C4 plant were concentrated with nC27 and nC29 homologues. Organic matter preserved in the Yellow River estuarine sediments showed strong terrestrial signals (C/N = 11–16, δ13C = −22.0‰ to −24.3‰). The distribution of long-chain n-alkanes in sediments also showed strong odd-to-even carbon chain predominance with nC29 and nC31 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 C3 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.