| China is a country with many lakes and reservoirs, so water from lakes and reservoirs is considered as an important freshwater resource of China as well as an indispensable natural resource for the development of industry and agriculture. However, as excessive nitrogen,phosphorus and other nutritional substances are received by lakes and reservoirs, phytoplankton and other aquatic organisms are bred abnormally, resulting in huge interference to the water environment and water ecosystem of lakes and reservoirs. As a result, eutrophication occurs.How to accurately reflect and evaluate the nutritional status of lakes and reservoirs is studied,thus providing a scientific basis for the ecological protection of water from lakes and reservoirs.On this basis, the physical and chemical indicators of water environment in Nierji Reservoir are monitored in this study, and the phytoplankton community composition and cell density are investigated. The temporal changing trend of each index is analyzed along with the use of various methods for water quality assessment, thereby carrying out a comprehensive evaluation of the eutrophication level in reservoirs. The eutrophication grade in reservoirs is also divided.On this basis, recommendations on reservoir protection are put forward. The main findings are as follows:1. Water environment indicators. The variance analysis was conducted for water environment indicators affecting the eutrophication of reservoirs, and their temporal changing trends were found. According to the correlation analysis of chlorophyll a and other water environment indicators: chlorophyll a, water temperature, the total phosphorus and pH were significantly or very significantly correlated(P <0.05 or P <0.01).2. Evaluation of physical and chemical indicators of the water environment. The single factor evaluation results showed that a number of water quality indicators had exceeded the standard(total nitrogen, total phosphorus and permanganate indicators). The EI results indicated that reservoir water was in the mild eutrophication- moderate eutrophication state. Values of TLI(TN), TLI(TP), TLI(CODMn), TLI(SD), and TLI(Chla) were all between 50 and 78,suggesting that water had entered into the full eutrophication.3. Phytoplankton community structure indicators. 51 kinds in 5 species of phytoplankton were identified in the dry season, wet season and normal river flow season of Nierji reservoir.The species number was: wet season> normal river flow season> dry season. The cell densityamong samples was greatly different, showing significant difference(P <0.05). The cell density order is: the middle part of Nierji Reservoir> the front part of Nierji dam> the end of Nierji Reservoir. Meanwhile, the dominant species was the microcystis aeruginosa and anabaena of cyanobacteria, the scenedesmus of chlorophyte, and the cyclotella and fragilaria of the bacillariophyta. These algae species were all indicative kinds of water eutrophication.4. Evaluation of the biological diversity of phytoplankton. In the wet season, the mean value of phytoplankton Shannon-Wiener index(H ') in the three samples was within the range of0.94-2.47, the variation range of Margalef index(D) was 0.98-1.74, and the evenness index(J)ranges from 0.14 to 0.48. By combining the water environmental indicators phytoplankton community structure indicators and biodiversity evaluation results, it suggested that different degrees of eutrophication had been shown in Nierji reservoir.5. Risk Assessment of potential blooms. Eight indexes, including the phytoplankton biodiversity, water temperature, pH, dissolved oxygen, permanganate index, total phosphorus,total nitrogen, and chlorophyll a were selected for the calculation of weight through the analytic hierarchy process(AHP), thus getting the potential bloom risk index of Nierji Reservoir. The bloom risk of three samples was divided according to the bloom risk levels, that wasthe middle part of Nierji Reservoir was in severe risk, and the front and end of the Reservoir were in mild risk. |
PDF Full Text Request