| In recent years, landscape water emerging out has become an important part of people’s living environment in the construction of city parks, residential areas and urban green space. The existence of landscape water adds vitality of the city, improves the city’s image, boosts life satisfaction and well-being of residents. However, due to people’s lack of sufficient knowledge about urban landscape water, there have been many different levels of pollution after running for some time, and some even eutrophication, water black smelly, mosquito breeding, the landscape water losed its function and undermined the living environment.In order to put forward reasonable control measures and effective operational management recommendations for landscape water pollution, researching its water quality variation and possible sources of pollution is the first thing we must do.This paper selected typical urban landscape water Hancheng Lake in Xi’an as a research object, analyzed the artificial lake water quality index through one-year monitoring; studied the water quality variation; analyzed the sources of pollution in Hancheng Lake; evaluated the water quality and nutritional status; studied the phosphorus of sediment adsorption and release characteristics in artificial lake, evaluated the risk of the release of phosphorus in sediments; Finally, according to the results put forward some recommendations. The main conclusions are as follows:(1) The nutrients of nitrogen and phosphorus concentrations in the lake were seriously excessive, higher than the V class water limit of Surface Water Environmental Standards. According to the features of the lake, the water quality index should reach IV class. Because the lake is a narrow river, like a channel, the water flowing speed from the inlet to outlet decreased from 0.3 to 0.01m/s, the index of TN、TP、turbidity were higher than the final section. The algae proliferated from the spring, peaked in the summer,with the outbreak of algae, pH rised and SD deteriorated.The DOM was humic acid, coming from the death of the plankton.(2) The nitrogen and phosphorus pollution were mainly from the water source Feng River, accounting for 97% and 92% respectively of the total input.The pollutants which were brought into water bodies by dry and wet deposition and runoff accounted for 2.9% and 7.9%.Net accumulation accounts of 21.4% and 18.6% respectively, sediments may be one potential source of pollution of the lake. The phosphorus content of the sediment was at medium level pollution. When the temperature reaches 30℃, the phosphorus of sediments released as the“source”, when the temperature is below 10℃, the sediment was adsorbed the phosphorus from the water bodies as a“sink”, when the temperature at 20℃, the sampling sites of 1, 2 and 3 points characterized as a “sink”, the sampling site of 4 point characterized as the“source”. When the temperature is high in summer, the phosphorus in the sediment was through a release risk.(3) The Hancheng Lake suffered the most serious degree of eutrophication in May, June and July of 2014,and at the same time, the algae was proliferating. The evaluation results from the inlet to the outlet at each sampling point were moderate eutrophication, the outlet trophic state index was less than the intake. The results of the water quality using gray clustering method showed that S1(inlet) of the sampling points was at Grade Ⅳ,and other points belonged to Grade Ⅲ. The results of sediments eutrophication risk evaluation showed that, the four sampling points were low-risk at 10℃ and 20℃, belonged to medium risk at 30℃.The temperature was beneficial to the release of phosphorus in sediments.At the same temperature, the phosphorus release risk of the 4th sampling point was higher than other points. |
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