[Hanfeng Pre-dam Commissioning Eutrophication Status and Control Evaluation in Three Gorges Reservoir]

Area of Science:

• Environmental Science
• Hydrology
• Eutrophication Studies

Background:

• The Three Gorges Reservoir features the unique Hanfeng Lake pre-dam system, China's largest artificial lake, designed to mitigate fluctuating water levels.
• The pre-dam system has demonstrably improved ecological benefits for landscapes, farmlands, and urban living.

Purpose of the Study:

• To assess the hydrological and water quality impacts of the Hanfeng Lake pre-dam system throughout its commissioning year.
• To evaluate the effectiveness of the pre-dam system in controlling eutrophication and reducing pollutant concentrations.

Main Methods:

• Layered hydrology and water quality monitoring of tributary runoff and lake sections.
• Analysis of 17 key indicators including physical (Temperature, pH, DO, TSS), chemical (Chl-a, TN, TP, SRP), and hydrological parameters.
• Application of Trophic Level Index (TLI) Water Quality Evaluation and factor analysis.

Main Results:

• Water quality varied seasonally, with the poorest conditions during initial drain/impoundment and the best at the regulating dam in February and October.
• Hanfeng Lake exhibited slight eutrophication, primarily indicated by elevated Dissolved Nitrogen (DN), Total Nitrogen (TN), nitrate-nitrogen (NO3--N), and Total Phosphorus (TP).
• The pre-dam system achieved significant reductions: 57.73% for chlorophyll-a, 28.12% for permanganate index, 20.15%-22.81% for SRP, TP, TN, TSS, NO2--N, DN, DP, and 16.92%-18.74% for NH4+-N and NO3--N, with an overall 15.74% reduction in the eutrophic index.

Conclusions:

• The Hanfeng Lake pre-dam system is highly effective in controlling eutrophication within the Three Gorges Reservoir.
• The system successfully reduces pollutant concentrations, demonstrating remarkable benefits for water quality management and ecological health.