Elemental and isotopic signatures of particulate organic carbon in the Zengjiang River, southern China

Riverine total suspended sediment (TSS) at the lower reach section of the Zengjiang River, a low-turbidity river in the southern China, was sampled on a 4-week basis from March 2002 to February 2003. The gross TSS was divided into sedimentary and suspended fractions (SED and SUS) by the sedimentation method. Organic carbon and nitrogen, C-14 and C-13 were analysed using an elemental analyser and accelerator mass spectrometer respectively. The results show that particulate organic carbon (POC) yield is 08 x 10(6) g km(-2) year(-1) in the Zengjiang River drainage basin, which is about one-tenth of that in the Zhujiang (Pearl) River drainage basin. The C/N ratio demonstrates that aquatic biomass is the major contributor to POC in the Zengjiang River. The average share of aquatic biomass in the SUS-fraction POC and SED-fraction POC is about 88.89% and 62.76% respectively, with a substantial seasonal variation. delta C-13 values of SUS-fraction POC (-2656 to -2289%) is slightly lighter than that of SED-fraction POC (-25.05 to -22.20%), indicating that the contribution of aquatic biomass to delta C-13 values is more pronounced in the SUS-fraction POC than in the SED-fraction POC. The `bomb'-C-14 signature is not detected in the POC of Zengjiang River, and the contribution from geological organic carbon is very little. Delta C-14 values of the SED-fraction POC vary from -44 to -223%, and the Delta C-14 values of the SUS-fraction POC vary from -33 to -165%. For most paired samples, the SED-fraction POC is generally more depleted in C-14 than that of its counterpart SUS-fraction POC. Compared with other small mountainous rivers, the C-14 enrichment of POC in the Zengjiang River indicates slight drainage basin erosion. Copyright (C) 2006 John Wiley & Sons, Ltd.