The black-odor mechanism of Yitong River was analyzed based on survey and monitoring results. We found that organic matter is the main pollution source of Yitong River and its tributaries. A black-odor evaluation model that can describe the pollution of the Yitong River water system was developed, and this model has the parameters I = 0.21 [CODCr] + 0.18 [DO] – 0.36[NH3-N] + 0.91. The model performance was satisfactory with a black-odor defining accuracy of 69%. Moreover, we found that CODCr, NH3-N, and DO are the influential factors of the Yitong River black-odor water body and that their threshold values when the water body transitioned to black odor were 109.2, 1.90, and 7.50 mg·L−1, respectively. We found that most of the Yitong River was polluted by six heavy metals, namely, As, Cd, Cr, Cu, Pb, and Zn. We used the Nemerow method to calculate the heavy metal pollution degree of each sampling point and found that 60% of the points were seriously polluted. Furthermore, we drew the heavy metal pollution distribution map of the Yitong River. Finally, we proposed an effective measure called new-type multistep constructed wetland to improve the water quality of Yitong River.

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