WATER QUALITY CHANGES AND EVALUATION AFTER DREDGING OF WUZHOU LAKE, CHINA

Abstract

Eutrophication caused by nutrient accumulation is a critical issue for small water bodies, yet the long-term effectiveness of dredging as a remediation strategy is not fully understood. This study evaluates water quality changes in Wuzhou Lake, China, over a 1.5-year period following dredging, to assess its short-to medium-term impacts on mitigating eutrophication. Water samples were collected from six sites before dredging (June 2021), after dredging (June 2022), and 1.5 years later (October 2023). Key water quality parameters, including pH, total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (NH₃-N), nitrate, and chlorophyll-a (Chla), were analyzed. Results showed significant reductions in TP, Chla, TN, and NH₃-N levels, while nitrate levels increased. Post-dredging, NH₃-N improved to Class II water standards, and Chla shifted from eutrophic to mesotrophic conditions. After 1.5 years, BOD and COD improved to Class IV and III, respectively, while TP declined Class V. These findings confirm short-term effectiveness of dredging in reducing nutrient pollution, with significant improvements observed between June 2021 and June 2022. However, the limited changes between June 2022 and October 2023 suggest that other factors, such as water stock changes, may also influence water quality. Complementary measures, such as expanding reed vegetation and reducing lotus density, are needed to ensure long-term ecosystem sustainability.