文献类型：期刊文献

英文题名：Nitrogen Cycling Across a Salinity Gradient From the Pearl River Estuary to Offshore: Insight From Nitrate Dual Isotopes

作者：Chen, Fajin[1,2,3];Deng, Ziyun[1,2];Lao, Qibin[1,2];Bian, Peiwang[1,2];Jin, Guangzhe[1,2,3];Zhu, Qingmei[1,2,3];Zhou, Xin[1,2];Chen, Chunqing[1,2]

机构：[1]Guangdong Ocean Univ, Coll Ocean & Meteorol, Zhanjiang, Peoples R China;[2]Guangdong Ocean Univ, Guangdong Prov Key Lab Coastal Ocean Variat & Dis, Zhanjiang, Peoples R China;[3]Guangdong Ocean Univ, Dept Educ Guangdong Prov, Key Lab Climate Resources & Environm Continental, Zhanjiang, Peoples R China

年份：2022

卷号：127

期号：5

外文期刊名：JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES

收录：SCI-EXPANDED(收录号：WOS:000788311000001)、、Scopus(收录号：2-s2.0-85130769456)、WOS

基金：We would like to thank professor Guodong Jia for his kind help and valuable advices. We would also like to thank professor Jie Xu for his support in collecting water samples. This study was supported by the Basic and Applied Basic Research Foundation of Guangdong Province (2019B1515120066), National Natural Science Foundation of China (U1901213) and Guangxi Natural Science Foundation of China (2020GXNSFBA297065).

语种：英文

外文关键词：nitrate; nitrate dual isotopes; Pearl River Estuary; Northern South China Sea; biogeochemistry

外文摘要：Dual isotope measurements were performed on nitrate (delta N-15-NO3- and delta O-18-NO3-) in the Pearl River Estuary (PRE) and the adjacent northern South China Sea (NSCS) to investigate nitrate sources and its biogeochemical processes during rainy season. Our results indicated that in the PRE, high nitrate levels were associated with the intense human activities in PRE delta, the sources of which included the reduced nitrogen (N) fertilizer (29%), SN (nitrate derived from soil N) (18%), manure and sewage (10%), and atmospheric deposition (7%). In the nearshore area, nitrate was characterized by relatively high delta N-15-NO3- and delta O-18-NO3- values suggestive of incomplete nitrate assimilation. Besides, nitrification might be significant in the intermediate and bottom waters due to ammonia release from remineralization of sinking and sedimented organic matter (OM). In the offshore area, nitrate was depleted due to nearly complete utilization, and delta N-15-NO3- and delta O-18-NO3- showed moderate values. In addition, delta O-18-NO3- exhibited a clear vertical gradient with a decrease from the surface to the bottom. A coupled nitrification-denitrification process in sediment porewater was supposed, which left isotope imprints in bottom waters of the offshore area. In surface waters from the nearshore to the offshore area, although assimilation was the prominent process, the delta N-15-NO3- and delta O-18-NO3- relationship deviated from the 1:1 line, suggesting significant contribution of atmospheric deposition that increased offshore. Our study suggests the external source of nitrate shifts from anthropogenic nitrogen to atmospheric source in the continuous river-estuary-ocean system, and nitrification-denitrification become more active as it goes seaward.