LI Weiye1, DING Hu1,2,3, HAN Xiaokun1,2,3, LIU Mingxuan1, LA Wei1, XU Aizhe1, LANG Yunchao1,2,3

（1. Institute of Surface-Earth System Science, School of Earth System Science, Tianjin University, Tianjin 300072, China; 

2. Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin 300072, China; 

3. Tianjin Bohai Rim Coastal Earth Critical Zone National Observation and Research Station, Tianjin 300072, China）

Abstract：The temporal and spatial variations of the sources of organic carbon (OC) and its influencing factors in two rivers, the Duliujian River and the Jiedijian River with different dam utilization status and land-use pattern, running into the western Bohai Bay, China, were investigated using chemometrics characters and different stable carbon isotopic compositions. The results showed that the carbon isotopic compositions of DOC (？13CDOC) in the Duliujian River and the Jiedijian River ranged from ？29.0‰ to ？24.3‰ and from ？28.4‰ to ？24.2‰, respectively, while the carbon isotopic compositions of POC (？13CPOC) in the two rivers varied from ？36.9‰ to ？22.0‰ and from ？35.7‰ to ？20.6‰, respectively. From the upstream to the offshore, the values of ？13CDOC and ？13CPOC in the two rivers showed an upward trend, except for some water bodies affected by human factors, and they were more positive in the summer than those in the early spring. The OC in two rivers was mainly derived from plankton, aquatic vascular plants, soil organic matter and urban sewage, with relative contributions of 49% ~ 59%、7% ~ 11%、13% ~ 16% and 17% ~ 27%, respectively. This study suggested that the sources and transformations of OC in two seagoing rivers under weak hydrodynamic conditions were mainly influenced by riverine metabolic processes (e.g. primary production and organic matter degradation) and the human activities (e.g. basin land-use types and damming). They had seasonal variations, with the impacts of riverine primary production higher in summer than that in early spring, and the impacts of human activities higher in early spring than those in summer. Moreover, the relative contributions of plankton to POC in the lower reach of the Duliujian River in summer and early spring were 9% and 16% higher than that in the lower reach of the Jiedijian River due to influence of dam in the estuary. The control processes of DIC in the lower reach of the Duliujian River in summer were significantly different from its upper reach and the Jiedijian River, dominated by primary production versus organic matter degradation. Hence, the results can provide scientific basis for better understanding the sources of OC and its influencing factors in the seagoing rivers under weak hydrodynamic conditions.

Key words：organic carbon; carbon isotopes; sources; seagoing rivers; estuaries; weak hydrodynamic conditions

EARTH AND ENVIRONMENT Vol.51, No.2, Tot No.352, 2023, Page 185