Temporal and Spatial Distribution of Dissolved Organic Nitrogen and Its Effects on the Community Structures of Phytoplankton in Xiamen Waters

FU Ting-ting; HUANG Zhi-wei; GUO Xiang; DU Qing-hong; CHEN Kai

doi:10.13651/j.cnki.fjnykj.2025.10.008

Abstract：In order to explore the spatial and temporal distribution characteristics of dissolved organic nitrogen concentration(DON)and urea concentration(Urea-N)in Xiamen waters and their effects on the phytoplankton community structure,the investigation of dissolved organic nitrogen,urea and phytoplankton community in Xiamen waters was carried out in April(spring)and August(summer)of 2022,and the spatial and temporal distribution characteristics and correlation of DON concentration,Urea-N concentration and phytoplankton communities in this water were analyzed.The results showed that:the average concentration of dissolved organic nitrogen in spring was higher than that in summer.The concentration of dissolved organic nitrogen in the bay was higher than that outside the bay,and the highest value in spring and summer appeared in the western water.The average value of urea concentration in summer was higher than that in spring,with a gradually decreasing trend from nearshore to offshore,and the highest concentrations in spring and summer were found in the Jiulong River estuary.The average abundance of phytoplankton in spring and summer was 8.4×106 cells·L-1 and 1.76×106 cells·L-1,respectively.The dominant species in spring included Chaetoceros,Skeletonema costatum,Chaetoceros debilis and so on,while the dominant species in summer included Skeletonema costatum Chaetoceros curvisetus and Rhizosolenia fragilissima.In spring,the average abundance of phytoplankton,diatoms,and dinoflagellates showed the high values in the western water and Tong'an Bay water,while the high value area appeared in the southeastern waters during summer.From the results of correlation analysis,it could be preliminarily concluded that:the salinity and dinoflagellate abundance were significantly negatively correlated with the DON concentration and Urea-N concentration.In spring,there was a significant positive correlation between temperature and total phytoplankton abundance.The research results showed that the main sources of DON and Urea-N in Xiamen waters were from the runoff input from the Jiulong River and the discharge input from land-based sources such as the domestic sewage and the industrial and agricultural wastewater.The effects of DON and Urea-N on the phytoplankton community structure(especially dinoflagellates)in Xiamen waters should not be ignored.