[Analysis， Evaluation， and Prediction Model of Water Quality in the Weihe River Basin]

As the largest tributary of the Yellow River， the Weihe River plays an important role in the ecological protection and high-quality development of the Yellow River Basin. Based on the new comprehensive water quality index （WQI-DET）， a comprehensive evaluation and analysis of the water quality status and spatiotemporal differences of the Weihe River was conducted using differential analysis methods. Principal component analysis was used to determine the main types of pollutants， and geographic detectors were used to quantify the possible driving factors of water quality in the basin. On this basis， machine learning algorithms and high-frequency monitoring data were used to simulate and predict WQI-DET. The study produced some important results： ① Organic pollution， eutrophication nutrient pollution， hexavalent chromium pollution， and fluoride pollution are all present in the Weihe River Basin， with poor water biodegradability， imbalanced nutrient structure， and severe nitrogen pollution. The water quality has not improved fundamentally in the past three years. The temporal and spatial differences in water quality indicators in the Weihe River Basin are significant， and there are seasonal characteristics of indicators such as organic pollution， nitrogen pollution， and turbidity. There are differences in water quality between different tributaries and the upstream， midstream， and downstream portions of the main stream， and pollutants show the characteristic of accumulating along the drainage. The non-point source pollution of agricultural production and the point source pollution of domestic wastewater are the main sources of organic pollutants and eutrophic nutrients in the Weihe River. At the same time， some tributaries of the Weihe River are affected by industrial source pollution， and heavy metal pollution is relatively serious. The geographical exploration results showed that the water quality of the watershed is influenced by both human activities and natural conditions. The machine learning model can accurately predict the WQI-DET of the Weihe River. Using six indicators from daily monitoring data， the WQI-DET （R²>0.92） was accurately simulated and calculated through the COA+BP model. Based on high-frequency daily monitoring data and the calculation results of the COA+BP model， a VMD+CNN-GUR-SE model was established to achieve calculation of future WQI-DET， thus realizing prediction and calculation of Weihe River water quality. The introduction of swarm intelligence optimization algorithms， variable mode decomposition， and attention mechanisms significantly improved the performance of the model.