SEASONAL VARIABILITY OF STABLE CARBON AND NITROGEN ISOTOPE OF SUSPENDED PARTICULATE MATTER IN THE CHANGJIANG RIVER

Abstract

Samples of suspended particulate matter were collected along the Nantong section, the Changjiang River, every two months during 1996-1999. Stable carbon and nitrogen isotopes and elemental C/N ratios were studied for source tracing of particulate organic matter. The δ 13 C and δ 15 N compositions of SPM from the section varied from -23.6‰ to -27.1‰ and 1.4‰ to 5.9‰, respectively. There were no significant differences in the δ 13 C and δ 15 N compositions between the sampling sites. The seasonal variation reflected the control of terrigenous inputs and in situ primarily production. δ 15 N and C/N ratio could provide limited information on the source because the original POM source signature may be lost or overprinted by biochemical alteration. Only δ 13 C ratios are reliable and a simple model of δ 13 C is used to estimate the proportions of terrigenous contribution for different seasons. Compared with the data published in literature, the δ 15 N composition of SPM in the Changjiang River is comparable with other estuaries. A simple model is used to estimate the contribution and variation of terrigenous organic matter inputs for the study area. Higher terrestrial inputs were observed in the summer of 1998, in response to a major flood event which occurred during that period of time.