文献类型：期刊文献

英文题名：Sources of nitrate in a heavily nitrogen pollution bay in Beibu Gulf, as identified using stable isotopes

作者：Cai, Shangjun[1,2];Lao, Qibin[1,2];Jin, Guangzhe[1,2];Chen, Chunqing[1,2];Zhou, Xin[1,2];Zhu, Qingmei[1,2];Lu, Xuan[1,2]

机构：[1]Guangdong Ocean Univ, Coll Ocean & meteorol, Key Lab Coastal Ocean Variat & Disaster Predict, Zhanjiang, Peoples R China;[2]Guangdong Ocean Univ, Resources & Environm Continental Shelf Sea & Deep, Key Lab Climate, Zhanjiang, Peoples R China

年份：2022

卷号：9

外文期刊名：FRONTIERS IN MARINE SCIENCE

收录：SCI-EXPANDED(收录号：WOS:000838442400001)、、Scopus(收录号：2-s2.0-85135800846)、WOS

基金：We would like to thank Marine Environmental Monitoring Centre of Beihai, State Oceanic Administration, for their support in collecting water samples. This study was supported by the Guangdong Provincial College Innovation Team Project(2019KCXTF021), the Guangxi Natural Science Foundation of China (2020GXNSFBA297065) and First-class Discipline Plan of Guangdong Province (080503032101, 231420003).

语种：英文

外文关键词：nitrate dual isotopes; ammonium isotope; nitrogen pollution; source; Beibu Gulf

外文摘要：Eutrophication, mainly caused by the oversupply of inorganic nitrogen and phosphate, has increased and become a serious environmental problem in the coastal bays of Beibu Gulf, a newly developing industry and port in South China. However, the sources of nitrate are poorly understood in the gulf. In this study, nitrate dual isotopes (delta N-15-NO3- and delta O-18-NO3-) and ammonium isotopes (delta N-15-NH4+) were measured during the rainy season to identify the nitrate sources and elucidate their biogeochemical processes in Xi Bay, a semi-enclosed bay that is strongly affected by human activities in the Beibu Gulf. The results showed that a high dissolved inorganic nitrogen (DIN, 10.24-99.09 mu mol L-1) was observed in Xi Bay, particularly in the bay mouth. The concentrations of DIN in the bay were 1.5 times higher than that in Qinzhou Bay and 1.7 times than that in Tieshangang Bay, which mainly influenced by the intensive human activities (i.e., industrial and port activities). In addition, lower values of delta N-15-NO3- and delta O-18-NO3- and higher values of delta N-15-NH4+ were observed in the upper bay, suggesting that microbial nitrification occurs in the upper bay, which was the dominant nitrate source in the upper bay (39%). In addition to nitrification, external sources, including sewage and manure (33%), soil N (15%) and fertilizer (11%), contributed to the higher nutrients in the upper bay. In the lower bay, severe nitrogen pollution led to a weaker impact of biological processes on isotopic fractionation, although a high Chl a level (average of 7.47 mu g L-1) was found in this region. The heavy nitrate pollution in the lower bay mainly originated from sewage and manure (54%), followed by soil N (26%) and fertilizer (17%). The contribution of the nitrate source from atmospheric deposition was relatively low in the bay (<3%). This study suggests that biogeochemical processes have little impact on nitrate dual isotopes under heavy nitrogen pollution, and isotopes are an ideal proxy for tracing nitrogen sources.