Comprehensive Water Quality Analysis of Deze Reservoir Using Multiple Evaluation Methods

To conduct a comprehensive analysis of water quality disparities in the Deze Reservoir and investigate the factors influencing its water quality, this study focuses on the Deze Reservoir as its research subject. It employs various evaluation methods, including the single-factor assessment method, the Nemero comprehensive pollution scoring method, the comprehensive pollution index method, principal component analysis, and the Canadian water quality index method, to scrutinize the dynamic changes in reservoir water quality and assess the reservoir's nutrient status.The findings revealed the following key points:(1) The single-factor assessment method swiftly classified the water quality of the Deze Reservoir as Class V, primarily influenced by a single factor, total nitrogen.(2) Both the Nemero index method and comprehensive pollution index method provided a more comprehensive assessment of the Deze Reservoir's water quality. Considering additional parameters for evaluation resulted in more accurate water quality scores, aligning better with the criteria for water quality assessment. Specifically, the Nemero index method indicated that the majority of the water bodies in the Deze Reservoir exhibited poor quality, with an average score of 7.17. Results from the comprehensive pollution index method suggested that the water bodies in the Deze Reservoir generally experienced mild pollution, with total nitrogen being the primary contributing factor (classified as Class IV, according to the standard index.(3) Principal component analysis revealed that nitrate, phosphate, dissolved oxygen, and total nitrogen had significant loadings on the principal components, making them the primary factors influencing water quality in the Deze Reservoir. Calculating and ranking the comprehensive scores from the principal component analysis method made it evident that pollution levels in Hallzitang and Sanchakou were more severe compared to the rest of the reservoir area. (4) Results from the Canadian water quality index method demonstrated that water quality in the Deze Reservoir exhibited both spatial and temporal patterns. Initially, water quality tended to deteriorate, followed by gradual improvements over time. Interestingly, a positive feedback relationship was observed between water intake and water quality. In summary, the assessment results obtained from the five water quality evaluation methods consistently highlighted total nitrogen as a crucial indicator of water pollution in the Deze Reservoir. This association can primarily be attributed to agricultural non-point source pollution in upstream areas, nutrient runoff from nearby agricultural land, and surface runoff contributing to water nutrient levels. From both spatial and temporal perspectives, the dominant factor influencing the Deze Reservoir's water quality is the influx of total nitrogen pollution.