Assessing Seasonal Nitrate Contamination by Nitrate Dual Isotopes in a Monsoon-Controlled Bay with Intensive Human Activities in South China

Jiacheng Li, Ruixue Cao, Qibin Lao, Fajin Chen, Chunqing Chen, Xin Zhou, Yafei Meng and Qingmei Zhu
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Jiacheng Li: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Ruixue Cao: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Qibin Lao: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Fajin Chen: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Chunqing Chen: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Xin Zhou: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Yafei Meng: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
Qingmei Zhu: College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China

IJERPH, 2020, vol. 17, issue 6, 1-16

Abstract: Nitrate (NO 3 − ) dual isotope analysis was performed in Zhanjiang Bay, which is a closed bay with intensive human activities in South China, to investigate seasonal changes in the main NO 3 − sources and their biogeochemical processes in the monsoon-controlled climate. The relatively low N/P ratios in Zhanjiang Bay suggests that nitrogen (N) is a limiting nutrient, which indicates that the increase of N is favorable for phytoplankton proliferation. However, a sufficient amount of ammonium was found in our study area owing to intensive human activities, which can support biological processes. Thus, less NO 3 − biological processes were found, indicating that NO 3 − isotopic characteristics may reveal details of the mixing from various sources. The Bayesian mixing model showed that NO 3 − in the upper bay originated from manure (43%), soil N (30%), N fertilizer (17%), and N precipitation (10%) during winter, which reflects the local human activities; while NO 3 - sources during summer were mainly N fertilizer (36%), soil N (32%), and manure (31%), indicating the source as the runoff from the upper river basin. Our results suggest that nitrate dual-isotope was very useful for tracing the main NO 3 − sources in the condition of the sufficient ammonium, and runoff exerted an important impact on the shift in NO 3 − sources between both the local source and the source from the upper river basin during the two seasons in this monsoon-controlled bay.

Keywords: nitrate dual isotopes; nitrate sources; Bayesian isotope mixing model; Zhanjiang Bay (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2020
References: View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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