Significantly depleted N-15 in suspended particulate organic matter indicating a strong influence of sewage loading in Daya Bay, China

• Published in: Science of The Total Environment
• Main Authors: Ke, Zhixin, Tan, Yehui, Huang, Liangmin, Liu, Jiaxing, Xiang, Chenhui, Zhao, Chunyu, Zhang, Jingping
• Format: Report
• Language: English
• Published: ELSEVIER SCIENCE BV 2019
• Subjects: Environmental Sciences & Ecology; Stable isotopes; Hypereutrophication; Estuarine ecosystem; Particulate organic matter; El Nino; River discharge; Environmental Sciences; ISOTOPIC COMPOSITION; STABLE-ISOTOPE; BIOGEOCHEMICAL PROCESSES; TEMPORAL VARIABILITY; SOUTHERN-OCEAN; RIVER-ESTUARY; C/N RATIOS; TOKYO BAY; EL-NINO; NITROGEN; Southern Ocean
• Online Access: http://ir.gig.ac.cn/handle/344008/45828; https://doi.org/10.1016/j.scitotenv.2018.09.076

The influence of anthropogenic nutrient loading on the stable isotopic signatures (delta C-13 and delta N-15) in the suspended particulate organic matter (SPOM) is still not fully understood. Water quality and the values of delta C-13 and delta N-15 in the SPOM were investigated in the surface water of Daya Bay during the spring of 2016 and 2017. The results indicated that the Dan'ao River is the main point source of nutrient pollution in Daya Bay. The delta N-15(POM) was very low in the Dan'ao River. The distribution pattern for this parameter in Daya Bay was determined chiefly by Dan'ao River discharge. Variations in delta N-15(POM) were ascribed mostly to the input of N-15-depleted DIN assimilated by the estuarine phytoplankton in Daya Bay. Extremely high NH4+ level in the river discharge should be responsible for the low delta N-15(POM) in the river water. The distribution of delta C-13(POM) in Daya Baywas regulated mainly by the input of C-13-depleted riverine SPOM. In the present study, the influence of phytoplankton growth on the delta(13) C-POM was not significant. Moreover, episodic rain events significantly influenced the temporal and spatial variations inwater quality and isotopic signature inDaya Bay. The relatively depleted (SPOMN)-N-15 in 2016 may have been correlated with the strong El Nino events of 2015-2016. Increases in the frequency and volumeof rainfall associatedwith El Ninomay have enhanced nutrient loading and the risk of algal red tide in the Daya Bay. In general, significant N-15 depletion in SPOMcould be the characteristic of hypereutrophic riverinewaters. This study suggested that delta N-15(POM) may be an effective indicator of the strength of riverine nutrient loading in Daya Bay. (C) 2018 Elsevier B.V. All rights reserved.