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 [COD_Cr] + 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 COD_Cr, 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.

The use of aquatic plants has recently become a popular technique for ecological restoration and purification of eutrophic rivers and lakes. In this paper, various technologies were studied and designed against the background of research and demonstration projects for pollution control in Dianchi Lake and comprehensive improvement of water quality. Different technical units were designed in the horizontal and vertical spaces of the water body. Horizontal spaces included plant buffers on the surface, algae enrichment and diversion, innovative floating beds, and emerging plant zones at the shoreline. Vertical spaces include ecological floating beds, ecological jellyfish, and ecological membrane coverings. Spatial growth patterns of aquatic plants were constructed with rational use of water space and integration with various techniques to maximize the absorption of nutrients in the lake, increase the transparency of the water, and alleviate lake eutrophication. The previous technologies were combined, and technical demonstrations were conducted using experiments. We set up an integrated technical demonstration district with an area of $0.25{\mathrm{km}}^2$ on the north shore of Dianchi Lake, and the results demonstrated the following: water transparency increased by $>50\mathrm{cm}$ ; algae biomass decreased by $>70\%$ ; and the percent removal of total phosphorous (TP), total nitrogen (TN), and chemical oxygen demand (${\mathrm{COD}}_{\mathrm{Mn}}$ ) was $>30\%$ .