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

Abstract

Listen

Translate article

Environmental context External nutrients giving rise to critical ecological issues of the coastal seawater. We investigated the nearshore nutrient concentrations and their sources in Xiamen Bay during 2013–18. Our results could provide theoretical support for controlling nearshore nutrient pollution. 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 nitrogen (N) and phosphorus (P) in the coastal area. Methodology The dissolved inorganic nitrogen (DIN) and phosphate (PO4–P) in coastal Xiamen were monitored from 2013 to 2018. The input of nitrogen from runoff in the coastal Xiamen was calculated from the runoff flow amount collected by Xiamen Marine and Fisheries Bureau. Atmospheric dry deposition of DIN was simulated using Williams model to analyse the potential sources of nutrients in the coastal Xiamen. Results High DIN and PO4–P levels occurred in the inner bay and decreased dramatically outside Xiamen Bay. The lowest values of DIN and PO4–P were observed 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 eutrophication for Xiamen Bay, providing more than 4 × 104 tonnes (Mg) of N input per year. The atmospheric N dry deposition provided more than 2.2 × 103 Mg of DIN input per year, which accounts for ~3.4–6.3% of the Jiulong River DIN input in the coastal Xiamen. Discussion The ratio of atmospheric nitrogen deposition to nitrogen enrichment from Jiulong River varied 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 into the major sources of N and P and highlights the importance of atmospheric nitrogen deposition to the DIN in the coastal city Xiamen.