Application of modified water quality index (WQI) in the assessment of coastal water quality in main aquaculture areas of Dalian, China

In the present study, a modified water quality index (WQI) was used to evaluate the water quality in south coastal aquaculture area of Dalian, Liaoning Province, China. Four main culture areas with 40 sampling stations were covered. Ten variables were selected for principal component analysis/factor analysis (PCA/FA), and the major factors affecting water quality were identified. The PCA results showed that these factors were mainly associated with nutrients, natural conditions and organic matter. The modified WQI was calculated to identify the classes of water quality and to evaluate the spatial and temporal changes among the sampling areas. The results revealed that the water quality generally performed the worst in June, and the best in October. The modified WQI proved to be a useful method for water quality classification and characterizing spatial and temporal changes in Dalian aquaculture areas.