Study On The Pollution Reduction Efficiency Of Submerged Vegetation Restoration In Gonghu Lake

At present, water pollution and water shortage are two major crises of freshwater resources the world faces. In particular, the phenomenon of "Algal Blooms" in water process the occurrence of growth trends, which is a great threat to people's drinking water safety. Therefore, controling of water sources protected areas and endogenous nutrient load, reducing the level of eutrophication of lakes and rivers, restoring the healthy freshwater ecosystems have become an important problem demanding to solute. The main contribution of this paper is to probe the pollution reduction technology in the river of water source protection area of Taihu Lake. The nutrient-rich river in water source protection area have been investigated and evaluated; Studied the photosynthetic characteristics of submerged aquatic in different lights and temperatures; Studied the influence on submerged vegetable on water turbidity and nutrition absorption muddy water. According to the laboratory results, enclosure experiments were set in jinshu Bay in Gonghu Lake to study the purification efficiency of submerged plants and restore the main river pollution reduction technology. Guided through the establishment of Daphnia magna -submerged vegetation ecological restoration and continuous cultivation of submerged plants adjustable bed on the Jinshu Bay River, the restoration effect was evaluated. The main results are as follows:1. Using field survey methods, we conducted an annual survey of water quality and macrophytes in Jinshu Harbor, Tianji Harbor and Longtang Harbor of Gonghu Lake of Taihu Lake, in 2008-2009. The results showed that: Gonghu Lake water resource areas had a greater risk of being eutrophic. The major pollution indicators was TN and TP. The annual average concentration of TN is 3.094 mg·L^-1,TP is 0.112 mg·L^-1. The total density phytoplankton in June of phytoplankton is significantly higher than that in March, which are 306.1×10⁴ ind·L^-1 and 165.9×10⁴ ind·L^-1, respectively. The mainly species are Cyanophyta, Chlorophyta and Bacillariophyta. Large aquatic plants in spring are only Phragmites communis, Species are increased in summer and autumn but with a single structure. Cabomba caroliniana is the main specie in Jinshu Harbor, which covers 90% of the river. Floating plants Spirodela polyrhiza cover up to 60%. There is no macrophytes in the three rivers in winter. In March and June the water quality are in a eutrophic state, which in March reached moderate eutrophication (LTI (Σ(= 64.113). Autumn and winter the water quality was in moderate nutrition (LTI (Σ) = 53.526). 2. Using PAM fluorescence measured PSⅡphotochemical efficiency (Fv/Fm) and other photosynthetic parameters of Vallisneria spiralis. In the condition of low-light, PSⅡphotochemical efficiency (Fv/Fm) values was not significant at different temperatures (P>0.05), and at 25℃, the experimental light within the Fv/Fm value of the highest average of 0.75. Changes of Initial fluorescence F₀ are not obvious with light (P> 0.05), low temperature had little impact on the F₀, F₀ have resistance to low temperature, and initial fluorescence F₀ response to high temperature 35℃increased relative to 25℃. Temperature on relative maximum electron transport rate is more significantly than light (P <0.01) .3. In high turbidity conditions, three kinds of submerged plants absorption capacity of the TN and NO₃^-N was obvious, the chlorophyll's decrease is obvious too, and the mixed cultivation of three plants absorb capacity was better; while PO₄^-P, TP, COD_Mn absorption is obvious. Three plants can significantly reduce the water turbidity, the reducing rates is significantly higher than the blank group (P<0.05) and mixed culture of three species, and the average decline rate of 99.73%.4. The concentrations in Vallisneria spiralis control, Elodea Canadensis control, Vallisneria spiralis + Elodea Canadensis control are reduced to 78.76%,70.20%,83.42%,81.85%,72.30%,75.55%,88,80%,78.80%,86.21%, respectively ,while the control group and the water outside the enclosures has a lesser extent nitrogen concentrations; 2)The control of Vallisneria spiralis + Elodea Canadensis have high reduction rate in decreasing the TP and COD_Mn, which were 86.97% and 76.16%, significantly higher than other controls(P<0.05)3) The effect of purifying water of Vallisneria spiralis and Elodea Canadensis is better in winter, and the purifying effect: Vallisneria spiralis + Elodea Canadensis>Vallisneria spiralis >Elodea Canadensis.5. Ecological rehabilitation system has been built villa on the Jinshu Bay River, the TN, TP, COD_Mn, NO₂, NO₃ removal significantly promoted (P <0.01), concentrations were decreased by 73.1% 47.1%, 78.0% and 71.1%. Transparency were improved 70cm. The water quality reach to the national surface standardⅢ.Adjustable bed technology of submerged plants on the river have a significantly higher removal rate of NH₄⁺-N than other forms of nitrogen.Purification of TP was higher than the PO₄^3--P. Load bearing capacity of exogenous experiments show that the introduction of 1/4 volume, the river ecosystem effects of nutrient reduction are high.With the exogenous nutrient loading continues to increase the efficiency of river purification process decreased, when the TN load 5310.018g, the removal rate of TN still reached 44%.