Temporal and spatial changes and eutrophication evaluation of dissolved inorganic nitrogen and phosphate in Laizhou Bay

LU Qingyuan; ZHANG Meng; ZHAO Kexin; HU Qingjing; DING dongsheng; QU Keming; CUI zhengguo

doi:10.13984/j.cnki.cn37-1141.2025.02.014

Abstract：To understand the temporal and spatial changes and eutrophication level of dissolved inorgan-ic nitrogen(DIN)and phosphate(PO43--P)in the Laizhou Bay and its adjacent waters,4 cruises were carried out from the spring(May)2020 to the winter(January)2021,referring to 40 survey stations.Based on the methods of organic pollution comprehensive index and potential eutrophication evaluation,we studied the concentrations and distributions of DIN and PO43--P and thus evaluated the levels of eu-trophication state and organic pollution.The results showed that the concentrations of DIN and PO43--P were basically the same between the surface and bottom in the Laizhou Bay,but showed significant seasonal changes.The concentration of DIN in summer and autumn was lower than that in spring and winter while the PO43--P had an opposite trend.NO3--N contributed more than 50％of the total DIN in four seasons,which was the main existence form of DIN.The distribution of DIN in the west coast was higher than that in the east in Laizhou Bay,and the high values mainly occurred in the Yellow River and Xiaoqing River estuaries,suggesting that terrigenous input had a great influence on DIN distribu-tion.The distribution of PO43--P was greatly affected by seasonal variation.Among four seasons,the water quality was polluted in the western and southern waters of the Laizhou Bay,and the water pollu-tion of the Yellow River and Xiaoqing River estuaries were more serious.In the past 60 years,the con-centrations of DIN and PO43--P increased initially and then decreases in Laizhou Bay.In summary,these research results provided data supports and theoretical references for the comprehensive govern-ance of Bohai Sea and the construction of beautiful bay in Shandong Province.