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Influence of the external N and P inputs on nutrients in the coastal area of Xiamen, China

Siying Dai, Jiehua Hu, Shanshan Wang , Siming Huang, Rong Tian, Shuhui Zhao, Yang Luo, Xiaoke Zhang, Xia Sun, Jinpei Yan

Abstract

Rationale: External nutrients greatly increase the critical ecological risks of the coastal seawater. Therefore, it is important to understand the sources and variation characteristics of N and P in the coastal area. Methodology: The dissolved inorganic nitrogen (DIN) and active phosphate (PO4-P) in coastal Xiamen were observed from 2013-2018. The input of the nitrogen from runoff in the coastal Xiamen was calculated via the runoff flow amount collected by Xiamen Marine and Fisheries Bureau. Atmospheric dry deposition of DIN was simulated using Williams model to analyze the potential sources of nutrients in the coastal Xiamen. Results: High DIN and PO4-P levels occurred in inner bay and decreased dramatically outside the Xiamen Bay. The lowest values of DIN and PO4-P were presented in summer, which is consistent with the temporal variation in nutrient inputs from the surface runoff and atmospheric deposition. The nutrient input of Jiulong River is the main source of Xiamen Bay, providing more than 4×104 t N input per year. The atmospheric N dry deposition provided more than 2.2×103 t DIN input per year, which accounts for about 3.4%-6.3% of the Jiulong River DIN input in the coastal Xiamen. Discussion: The ratio of atmospheric deposition to Jiulong River input nitrogen was from 0.21 to 0.40, indicating that atmospheric nitrogen deposition was an important contributor to the coastal nutrient in Xiamen. This study provides an insight to understand the major sources of N and P and the importance of atmospheric nitrogen deposition to the DIN in the coastal Xiamen.

EN24060  Accepted 25 November 2024

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