| Eutrophication phenomenon has appeared large-proportion in tributaries to the Three Gorges Reservoir after impoundment because its hydrodynamics condition has been changed obviously. The obvious characters are Chlorophyll-a(Chla) concentration increased (The Chla concentration even reach hundreds milligramme per stere in serious area), transparence and dissolving oxygen reduced. Not only it can lead to water function obstacle, affect breed aquatics and sightseeing, but also the algae toxin and derivative it procreant are seriously harmful to health,survival and multiplication of people. This phenomenon has aroused highly attention of the departments. But the history of eutrophication investigation is short, and its occurrence, development and control are complex. Thus, till now, there are no unified standards of index system, appraise criterion and method which evaluate the water eutrophication in the world. In order to guarantee safety of water environment in the Three Gorges Reservoir, water quality actualities of 10 typical tributaries were monitored and appraised, and the experiential eutrophication models were founded in this thesis. Algae growth mechanism and its effect factors were analyzed, active algae cell analytical method and mensuration were brought forward, and trial studies of algae growth in tributaries were carried. The contents and results were summarized as below.①Eutrophication of 10 tributaries to the Three Gorges Reservoir was studied. It showed that different degrees of eutrophication were occurred in 10 tributaries from 2004 to 2006.The dominance algae were Bacillariophyta, Pyrrophyta, Cyanophyta and Chlorophyta, but sometimes were Cryptophyta and others.②The experiential model of eutrophication of the tributaries to the Three Gorges Reservoir was validated. It showed that the eligibility ration of Chla-TP model, Chla-CODMn model, Chla-TN model and Chla-SD model would be 77%, 75%,68% and 67% respectively in 57 models which has remarkable meaning(α=0.10), if taking absolute value of RE% of Chla forecast value and monitoring value less than 80% as eligible date.③Algae growth mechanism of the tributaries in the Three Gorges Reservoir was analyzed. It showed that the necessary conditions of eutrophication were appropriate temperature and abundance illumination, abundance nitrogen and phosphorus nutrients, slow flow velocity. ④Algae growth experiments of Daning River in the Three Gorges Reservoir were carried. Results showed that:1) In 0~27mg/m3, the concentration of Chla measured by active algae cell analytical method(x) is directly proportional to the value measured by acetone extraction spectrophotometry(y). The regression equation was y=4.15x+2.48 (mg/m3), R2=0.9985. T-test showed that the equation has remarkable meaning (α=0.01).2) The optimal condition for algal growth was that the water temperature and illumination were 20℃and 8000Lx, the concentrations of DIN and PO4-P were 85.71μmol/L and 2.86μmol/L respectively. Phosphorus was the limiting nutrition element for algal growth, and the optimal ratio of nitrogen to phosphorus was 30:1. Under the optimal condition, the specific growth rate was 1.03/d at the expotential phase, and the maximum Chla concentration was 110 mg/L at the stationary phase.3) Under the conditions of that the water temperature and illumination were 20℃and 8000Lx respectively, and the ratio of phosphorus and nitrogen concentrations was 30:1, the maximum growth rate were 1.16/ d both nitrogen and phosphorus, and the half-saturated constants of nitrogen-limit and phosphorus-limit were 8.65μmol/L and 0.29μmol/L respectively.
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