Carbon and nitrogen stable isotopes as tracers to source organic matter in the Yangtze estuary

In this article, we mainly focus on the geochemical characteristics of stable carbon and nitrogen isotopes in order to trace the source and fate of organic matter in the Yangtze estuary and its tidal flat sediments. According to the features of physical geographical environment and the discrepancy in the effects of human activities in the study area, 12 typical sampling stations were selected along the Yangtze estuarine and coastal line. Based on the analysis of stable carbon and nitrogen isotopes in the tidal flat superfacial sediments from the Yangtze estuary, it was found that the ratios of stable carbon and nitrogen isotopes were respectively -29.80‰∼-23.7‰ and 1.0‰∼5.5‰ in the flood seasons, while they were -27.3‰∼-25.6‰ and 1.6‰∼7.7‰ in the dry seasons respectively, indicating that the seasonal distribution of discharges from the Yangtze River has significantly affected the seasonal variation of stable carbon and nitrogen isotopes in sedimentary organic matter. In general, the distribution of stable carbon and nitrogen isotopes revealed the mixing inputs of terrigenous and marine organic matter controlled the stable carbon and nitrogen isotope compositions in sedimentary organic matter. However, a series of physical, chemical and biogeochemical processes occurring in the local environments, to some extent, have the significant influence on the stable carbon and nitrogen isotope compositions in organic matter.