Sources of nitrate in Xiangshan Bay (China), as identified using nitrogen and oxygen isotopes. (31st July 2018)

• Record Type: Journal Article
• Authors: Yang, Zhi; Chen, Jianfang; Li, Hongliang; Jin, Haiyan; Gao, Shenquan; Ji, Zhongqiang; Zhu, Yong; Ran, Lihua; Zhang, Jingjing; Liao, Yibo; Bai, Youcheng
• Is Part Of: Estuarine, coastal and shelf science. Volume 207(2018)
• Page Start: 109
• Page End: 118
• Publication Date: 2018-07-31
• Subjects: Nitrogen isotopes -- Oxygen isotopes -- Nitrogen cycle -- Nitrates -- Nitrate sources -- China, Xiangshan Bay; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2018.02.019
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: Eutrophication, mainly caused by the oversupply of nitrate (NO3 − ) and phosphate, has become a serious environmental problem in Xiangshan Bay (east China), but the sources of the nitrate are poorly understood. In this study, the estuarine distributions of dual stable isotopes (δ 15 N and δ 18 O) of NO3 − measured in May 2012 were used in combination with concurrent measurements of salinity, pH, dissolved oxygen, and nutrients (nitrate, nitrite, ammonium, and phosphate) to investigate NO3 − sources and the processes that control NO3 − distributions within the bay. In the lower bay, high concentrations of NO3 − (up to 60.6 μmol L −1 ), an N/P ratio of 52, and low values of nitrate δ 15 N (δ 15 NNO3 = 5.7‰–6.7‰) and δ 18 O (δ 18 ONO3 = 1.8‰–3.5‰) indicate that NO3 − in this area was likely from the Changjiang and Qiantangjiang rivers as well as local nitrification-associated inputs. In the upper bay, constituent concentrations and high values of δ 15 NNO3 (up to 8.8‰) and δ 18 ONO3 (up to 6.8‰) suggest that NO3 − distributions here were controlled mainly by the mixing of coastal and fresh waters, phytoplankton assimilation, and inputs of riverine NO3 −, possibly derived from manure and sewage. Spatial variations of Δ(15, 18), the nitrate δ 15 N-to-δ 18 O anomaly, is possibly resulted from the different water residence times across the bay, which could in turn lead to different degrees of nitrification or variable amounts of NO3 − from atmospheric deposition.