Evaluation of Winter Water Purification Efficiency in Lakes by Wetland Ecological Restoration Projects

A study was conducted to evaluate the water quality improvement effects of constructed wetlands on natural lakes, selecting the constructed wetland in the Sino-French Peninsula Town of Houguan Lake in Wuhan as the research subject. The purification performance of the constructed wetland and the water quality status of Houguan Lake were monitored and assessed over a five-month period from November 2024 to March 2025. Field sampling was conducted at five monitoring points within the wetland and Houguan Lake, focusing on five water quality parameters: pH, total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NHs+- N), and chemical oxygen demand (COD). The evaluation employed the single-factor index method, the Nemerow index method, and the Water Quality Index (WQI) method for a comprehensive assessment. The results demonstrated that the effluent quality of the constructed wetland consistently met Class II standards, significantly outperforming the Class III water quality of Houguan Lake. Average removal rates for total nitrogen (TN), total phosphorus (TP), and ammoniacal nitrogen (NH3+-N) were 30%, 60%, and 32% respectively, whilst chemical oxygen demand (COD) removal efficiency remained relatively low at 20%. Seasonal analysis revealed that low winter temperatures reduced the removal rates of TN and TP. In February, phosphorus release from decomposing plant residues led to a peak TP concentration in Houguan Lake (0.117 mg/L, exceeding Class III standards). By March, purification efficiency recovered as temperatures rose. Water Quality Index (WQI) assessment indicated that Chemical Oxygen Demand (COD) was the primary influencing factor in Houguan Lake, whereas Total Nitrogen (TN) dominated in the constructed wetland, with Total Phosphorus (TP) having a minor impact in both. The Nemerow index method confirmed that the constructed wetland's water quality was superior to that of Houguan Lake, though the results were susceptible to outlier interference. To enhance performance, it is recommended to optimise hydraulic loading to improve COD removal efficiency and strengthen operational management during winter. This research provides a scientific basis for optimising constructed wetland operation under low-temperature conditions and supporting lake ecological restoration.