Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China

Chunqing Chen; Qibin Lao; Fajin Chen; Guangzhe Jin; Jiacheng Li; Qingmei Zhu

doi:10.1007/s13131-024-2373-0

Volume 43 Issue 6

Jun. 2024

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Chunqing Chen, Qibin Lao, Fajin Chen, Guangzhe Jin, Jiacheng Li, Qingmei Zhu. Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China[J]. Acta Oceanologica Sinica, 2024, 43(6): 60-70. doi: 10.1007/s13131-024-2373-0

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Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China

doi: 10.1007/s13131-024-2373-0

Chunqing Chen^{1, 2},
Qibin Lao^{1, 2},
Fajin Chen^{1, 2, 3, 4
,
,},
Guangzhe Jin^{1, 3, 4},
Jiacheng Li¹,
Qingmei Zhu^{1, 3, 4}

1.
College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
2.
School of Chemistry and Environment, Guangdong Ocean University, Zhanjiang 524088, China
3.
Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
4.
Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang 524088, China

Funds: The National Natural Science Foundation of China under contract Nos 42276047, 92158201 and U1901213; the Entrepreneurship Project of Shantou under contract No. 2021112176541391; the Scientific Research Start-Up Foundation of Shantou University under contract No. NTF20006.

More Information

Corresponding author: fjchen@gdou.edu.cn
Received Date: 2023-12-25
Accepted Date: 2024-03-15

Available Online: 2024-07-10

Publish Date: 2024-06-30

Abstract

Abstract

Eutrophication in coastal waters has been increasing remarkably, severely impacting the water quality in mariculture bays. In this study, we conducted multiple isotopic measurements on suspended particulate nitrogen (δ¹⁵N-PN) and dissolved nitrate (δ¹⁵N-${\mathrm{NO}}_3^- $ and δ¹⁸O-${\mathrm{NO}}_3^- $) in Zhanjiang Bay, a typical mariculture bay with a high level of eutrophication in South China, to investigate the changes in nitrogen sources and their cycling between the rainy and dry seasons. During the rainy season, the study found no significant relation between δ¹⁵N-PN and δ¹⁵N-${\mathrm{NO}}_3^- $ due to the impact of heavy rainfall and terrestrial erosion. In the upper bay, a slight nitrate loss and slightly higher δ¹⁵N-${\mathrm{NO}}_3^- $ and δ¹⁸O-${\mathrm{NO}}_3^- $ values were observed , attributed to intense physical sediment-water interactions. Despite some fluctuations, nitrate concentrations in the lower bay mainly aligned with the theoretical mixing line during the rainy season, suggesting that nitrate was primarily influenced by terrestrial erosion and that nitrate isotopes resembled the source. Consequently, the isotopic values of nitrate can be used for source apportionment in the rainy season. The results indicated that soil nitrogen (36%) and manure and sewage (33%) were the predominant nitrogen sources contributing to nitrogen loads during this period. In contrast, the dry season saw a deficient ammonium concentration (<0.2 μmol/L) in the bay, due to nearly complete consumption by phytoplankton during the red tide period. Additionally, the significant loss of nitrate and simultaneous increase in the stable isotopes of dissolved and particulate nitrogen suggest a strong coupling of assimilation and mineralization during the dry season. More active biogeochemical processes during the dry season may be related to decreased runoff and increased water retention time. Overall, our study illustrated the major seasonal nitrogen sources and their dynamics in Zhanjiang Bay, providing valuable insights for formulating effective policies to mitigate eutrophication in mariculture bays.
- nitrogen,
- stable nitrogen isotopes,
- biogeochemical processes,
- eutrophication,
- Zhanjiang Bay

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References(36)

References

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