Abstract: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, 14 C and 13 C were analysed using an elemental analyser and accelerator mass spectrometer respectively. The results show that particulate organic carbon (POC) yield is 0Ð8 ð 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 88Ð89% and 62Ð76% respectively, with a substantial seasonal variation. υ 13 C values of SUS-fraction POC ( 26Ð56 to 22Ð89‰) is slightly lighter than that of SED-fraction POC ( 25Ð05 to 22Ð20‰), indicating that the contribution of aquatic biomass to υ 13 C values is more pronounced in the SUS-fraction POC than in the SED-fraction POC. The 'bomb'-14 C signature is not detected in the POC of Zengjiang River, and the contribution from geological organic carbon is very little. 14 C values of the SED-fraction POC vary from 44 to 223‰, and the 14 C values of the SUS-fraction POC vary from 33 to 165‰. For most paired samples, the SED-fraction POC is generally more depleted in 14 C than that of its counterpart SUS-fraction POC. Compared with other small mountainous rivers, the 14 C enrichment of POC in the Zengjiang River indicates slight drainage basin erosion.
Inorganic carbon, the great part of the riverine carbon exported to the ocean, plays an important role in the global carbon cycle and ultimately impacts the coupled carbon-climate system. An overview was made on both methods and results of the riverine inorganic carbon researches. In addition to routine in situ survey, measurement and calculation, the direct precipitation method and the gas evolution technique were commonly used to analyze dissolved inorganic carbon in natural water samples. Soil CO2, carbonate minerals and atmospheric CO2 incorporated into riverine inorganic carbon pool via different means, with bicarbonate ion being the dominant component. The concentration of inorganic carbon, the composition of carbon isotopes (~1~C and AI4C), and their temporal or spatial variations in the streams were controlled by carbon input, output and changes of carbon biogeochemistry within the riverine system. More accurate flux estimation, better understanding of different influential processes, and quantitative determination of various inputs or outputs need to be well researched in future.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.