Sources and distribution of carbon within the Yangtze River system

Dissolved, particulate, soil and plant samples were collected from the Yangtze River (Changjiang) system in May 1997 and May 2003 to determine the sources and distribution of organic and inorganic matter within the river system. Average dissolved organic carbon (DOC) concentrations within the main stream were 105 mu M C in 1997 and 108 mu M C in 2003. Particulate organic carbon (POC) ranged from 0.5% to 2.5% of total suspended matter (TSM). Both dissolved inorganic carbon (DIC) and particulate inorganic carbon (PIC) concentrations decreased from upper to lower reaches of the river, within the ranges 1.2-2.7 mM and 0.08-4.3% of TSM, respectively. delta C-13 and delta N-15 values for tributaries and the main stream varied from -26.8 parts per thousand to -25.1 parts per thousand and 2.87 to 6.0 parts per thousand, respectively. A large spatial variation in particulate organic matter (POM) is recorded along the main stream, probably due to the contributions of TSM from major tributaries and POM input from local vegetation sources. The dominance of C-3 plants throughout the entire basin is indicated by delta C-13 and delta 15N values, which range from -28.8 parts per thousand to -24.3 parts per thousand and from -0.9 parts per thousand to 5.5 parts per thousand, respectively. The VC and delta N-15 values of organic matter within surface soil from alongside tributaries and the main stream vary from -28.9 parts per thousand to -24.3 parts per thousand and 2.7 parts per thousand to 4.5 parts per thousand, respectively. Although these differences are subtle, there is a slight enrichment of N-15 in soils along the main stream. Various approaches, Such as C/N and stable isotopes, were used to trace the sources of organic matter within the river. Riverine POM is mostly derived from soil; the contribution from phytoplankton is minor and difficult to trace via the composition of particles. POC flux has decreased from > 5 x 10(6) t yr(-1) during the period 1960-1980 to about 2 x 10(6) t yr(-1) in 1997. This trend can be explained by decreasing sediment load within the Yangtze River. The export of TOC from the Yangtze River at the end of the 20th Century is approximately equivalent to that of the Zaire River, less than that of the Amazon River, and higher than that of other large rivers such as the Mississippi. Large amounts of DOC and POC were transported to coastal areas of the East China Sea over a short period (luring 1998 flood events, containing large amounts of nutrients and pollutants. Such an event could be an important trigger for coastal environmental problems and changes to the health of ecosystems. (c) 2006 Elsevier Ltd. All rights reserved.