| Urban landscape water is an integral part of the living environment. Eutrophication and algae blooms can seriously affect the ornamental and ecosystem service functions of the waters. In order to make accurate judgement of the mutrition status for landscape waters in Shanghai, understand the eutrophication process and forecast the trend, the main factors and criteria of eutrophication evaluation for urban landscape waters were analyzed and discussed based on the investigation result of Bo Fangfang (2009) for 15 typical landscape waters located in Shanghai including Century Park, Zhongshan Park etc. A fuzzy neural network model based on T-S was established with MATLAB, which can determine the nutrition status of the water body rapidly and effectively, and verified to be reliable and superior through comparison with TLI method, AHP-PCA method and SCO method. From July 2009 to November 2010, Gongqing Forest Park and other six main landscape waters in Shanghai were tracked. By comparing algae bloom water samples and non-bloom water samples, the warning line of water bloom for Shanghai landscape waters was preliminary determined and the early warning monitoring indicators were identified. The main results are as follows:1 Eutrophication evaluationEvaluation factors:Five indicators including chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), transparency (SD) and permanganate index (CODMn) are chosen to be the eutrophication evaluation factors for Shanghai landscape waters.Evaluation criteria: According to the range of the water quality indicators, the nutrition status of urban landscape waters is divided into eight levels:oligotrophic, oligo-meso trophic, mesotrophic, meso-light eutrophic, light eutrophic, meso-euthrophic, hyper-euthrophic, and super euthrophic. Evaluation model:A fuzzy neural network model based on T-S with the topological structure of 5-15-1 is established, which takes the five evaluation factors as input variables and the nutrition level as the output variable. The corresponding relationship between the output value (a) and the nutrition level is defined according to the rounding-off method as following: a<1.5 is oligotrophic,1.5≤a<2.5 is oligo-meso trophic,2.5≤a<3.5 is mesotrophic,3.5≤a<4.5 is meso-light eutrophic, 4.5≤a<5.5 is light euthrophic,5.5≤a<6.5 is meso-euthrophic,6.5≤a<7.5 is hyper-euthrophic, a≥7.5 is super euthrophic.Evaluation application: The established eutrophication evaluation system was used to evaluate the 75 water samples and their distribution in different nutrition levels was as following: super euthrophic 3%, hyper-euthrophic 3%, meso-euthrophic 20%, light eutrophic 31%, meso-light eutrophic 21%, mesotrophic 13%, oligo-meso trophic 9%, oligotrophic 0%. Almost 56% of the water samples are eutrophic.The result can reflect the actural nutrition level of the waters well. Most waters are in different nutrition status in different time. The nutrition status of some individuals fluctuates a lot. It is reasonable to make seperate evaluation for the same water body at different time for urban landscape waters.2 Water bloom early warningCompariosn of key factors:The five dominant factors of water bloom for Shanghai landscape waters are chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), transparency (SD) and permanganate index (CODMn).Except that permanganate index of the algae bloom water is higher than the non-bloom water, other indicators of the two types of different water samples have no big difference.Compariosn of other indicators:There's no obvious difference between the algae bloom water and the non-bloom water on the range of dissolved oxygen (DO), ammonia nitrogen (NH3-N), pH and water temperature (Tw).Compariosn of algae cells density: The range of algae cells density of algae bloom water samples is 212.7 X 105-423.5×105 cells/L and non-bloom water samples 10.3×105-377.2×105 cells/L. The algae cells density of algae bloom water samples is high. But some non-bloom water samples also have very high cells density, even higher than the algae bloom ones.Compariosn of nutrition status:For the algae bloom water samples, the model value ranges from 5.57 to 7.11. The nutrition levels of them are all above meso-euthrophic. For the non-bloom water samples, the model value ranges from 1.48 to 7.76. The nutrition status of them could be at any level from oligotrophic to super eutrophic.The warning line of water bloom:Model value≥5.5 is set as the warning line of water bloom for Shanghai landscape waters, which means the nutrition level of the water body is above meso-euthrophic.Early warning monitoring indicators:According to the warning line of water bloom, the monitoring indicator for Shanghai landscape waters should be chlorophyll a (Ch1-a), total phosphorus (TP), total nitrogen (TN), transparency (SD) and permanganate index (CODMn).
|
PDF Full Text Request