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[Evaluation and ecological control of the eutrophic state of Gudong reservoir].

The eutrophic state of Gudong reservoir and relative factors were investigated and evaluated. Then a comprehensive ecological control technology was proposed. The amount of herbivorous fish and filter-feeding fish was determined both through theoretic calculation and experimental test. The results demonstrated that Potamogeton crispus was the dominant grass over 80%, the phytoplankton biomass was 22.32 mg/L, and the total phosphors was 0.310 g/(m2 x a), which suggested that Gudong reservoir was on the eutrophic state. Through ecological engineering by controlling the biomass of Hypophthalmichthys molitrix and Aristichthys nobilis at 19-25 g/m3, the algae biomass was reduced from 14.6 mg/L to 3 mg/L at September, the annual average total phosphorous, nitrogen and permanganate index were reduced from 0.06 mg/L, 3.06 mg/L and 4.42 mg/L to 0.03 mg/L, 1.58 mg/L and 3.73 mg/L, respectively, which showed that the reservoir water quality has been obviously improved. Also, the flocculant dosage to treat this reservoir water was reduced from 42 g/m3 to 25 g/m3 after ecologic control. The results showed that the eutrophication could be controlled effectively by adopting the ecological restoration technology with rationally introducing the herbivorous fish and filter-feeding fish, and significant benefits can also be achieved.