Spatiotemporal evolution of chemical oxygen demand and its impact factors in Laizhou bay

ZHANG Meng; LU Qingyuan; LIU Ying; ZHANG Yan; WANG Dawei; HU Qingjing; CUI Zhengguo

doi:10.13984/j.cnki.cn37-1141.2025.03.020

Abstract：Laizhou bay is an important spawning ground in the Bohai sea and the temporal and spatial changes of chemical oxygen demand(COD)have an important impact on fishery resources and ecologi-cal environment.In order to understand seasonal changes of chemical oxygen demand(COD)in Laizhou bay,four on-site surveys were conducted during 2020-2021 and the organic pollution index method was employed to evaluate the survey area.Based on the relevant literature and the monitoring data of our laboratory from 1979 to 2021,the temporal and spatial trend of chemical oxygen demand(COD)concentration in Laizhou bay and its impact factors were discussed.The results showed that the seasonal chemical oxygen demand(COD)concentration in the northern Laizhou bay was lower than that in the south bank,and the high values occurred in the Weihe,Yuhe and Xiaoqing river estuaries.The organic pollution index illustrated that the polluted sea area was the largest in summer and mainly concentrated in the southwest coast of Laizhou bay.The spatial distribution of chemical oxygen demand(COD)in different periods indicated that the area with high chemical oxygen demand(COD)content tended to shrink and was still mainly concentrated in the southwest coast of Laizhou bay.The chemical oxygen demand(COD)concentration in Laizhou bay had shown an"M-type"trend in the past 40 years,and it decreased after 2014 obviously.The land-source transportation of rivers such as the Yellow river and Xiaoqing river,and the rapid economic development around the Laizhou bay had a significant im-pact on the temporal and spatial changes of chemical oxygen demand(COD).This work can provide scientific basis for further analysis of the spatiotemporal evolution trend of organic pollution in Laizhou bay.