Water quality analysis and source apportionment in estuaries along the coast of the Bohai Sea, North China

High-dimensional data (a dataset with many features) were collected from 64 sampling sites to analyze the water quality in estuaries along the coast of the Bohai Sea, North China. The twenty-five water quality parameters analyzed were collected monthly from January 2021 to December 2021. Multivariate statistical techniques such as the absolute principal component score-multiple linear regression model (APCS-MLR), correlation analysis, and analysis of variance were used to identify and quantify the potential sources or factors affecting water quality and to analyze the spatial-temporal variation in water quality. The water quality indices (WQIs), ranging from 67.96 to 70.67, showed that the water quality was at an intermediate level in the estuaries during both the flood and nonflood seasons. The concentrations of total phosphorus (TP), ammonia N (AN), and organic pollutants were greater in the Haihe River Basin than in the Liaohe River and Huanghe-Huaihe River Basins. The concentration of total nitrogen (TN) in the Haihe River Basin was lower than that in the Liaohe River and Huanghe-Huaihe River Basins. Heavy metal concentrations in the Liaohe River Basin were greater than those in the Haihe River and Huanghe-Huaihe River Basins. The annual mean concentrations of AN in the estuaries of the Haihe, Liaohe, and Huanghe (Yellow) rivers exhibited significant decreasing trends from 2013 to 2022, but no significant decreasing trends were found for permanganate index (COD_Mn) or the TP. The concentrations of TN and AN were lower in the flood season than in the nonflood season, and the TP concentration was greater in the flood season than in the nonflood season. However, the concentrations of organic pollutants did not exhibit significant differences. Domestic sewage and industrial wastewater, substance exchange between air and water, nonpoint sources from rural and urban areas, and aquaculture wastewater were the major sources or factors responsible for water pollution in the estuaries.