The Effects Of Algae Habitats On Eutrophication Of Landscape Lake Replenished By Reclaimed Water In North City Of China

With the development of society, people’s demand for landscape water is more strongly. At present, the northern city of our country is water scarcity, water scarcity has become a major bottleneck to restrict the development of landscape water. Water quality and quantity of recycled water is stable. If reusing recycled water back to landscape water can not only save water resources, but also reduce the pollution of the environment. At the same time, the needs on the water features of people are met. But rich content of nitrogen and phosphorus and other nutrients in the reclaimed water, that is eutrophic water quality, is easy explosion "blooms", leading to the water quality deterioration and loss of water landscape function. Thus, scholars from various countries focus their points on controlling the growth of algae and reducing algal density to prevent water bloom. Generally believed that the growth rate of algae is related with light, water temperature, nutrient concentration and other factors, but there are many scholars think velocity, depth and other hydrological factors as important factors affecting the growth of algae. For most of water body, velocity, depth and cross-sectional width and other factors are controllable artificial factors, therefore, studying the relationship between the flow rate, depth and width section with the growth of algae has significant importance. As we known, the formation of algal blooms generally experiences dormancy, recovery, growth and aggregation four stages, which is transformed by comprehensive effect of rainfall, temperature, nutrient concentration and structure, p H, flow velocity, water depth and section width extrinsic. And "comprehensive inducing factor" led to algae bloom phase transformation to another algal blooms stage. Therefore, identifying "comprehensive inducing factor" which exists in the algae blooms four-stage process has very positive economic significance and social effects in studying algal bloom formation mechanism, forecasting and controlling the occurrence of algal blooms.To study the contribution of velocity, depth and section width hydraulic factors to algal blooms, basing on the water quality and hydrological features data of Tianjin Harbor Ecological Wetland Park during October 2013~May 2014, the targeted lake was clustered into three water fields by using various multivariate statistical techniques including correlation analysis and cluster analysis. The spatial and temporal distribution of water temperature, DO, p H, nitrogen, phosphorus and Chl.a in the clustered water were studied. Correlation analysis showed that DO, nitrate nitrogen, TN, TP and flow velocity were positively correlated, while water temperature, SS and flow velocity were negatively correlated, respectively. Chl.a was positively related with water depth, whereas TN, nitrate nitrogen were negatively related with water depth.However there was no significant correlation between physicochemical indexes and section width. During the survey, the rate of total nitrogen to total phosphorus(TN/TP) was transforming from nitrogen limitation state(N/P<7)to eutrophication state. In addition,a eutrophication risk assessment method showed that the targeted lake which was selected reclaimed water as a supplement was already in middle eutrophication, the main factors which influenced water quality were COD and TP.Three data analysis and processing methods including Q-type hierarchical cluster analysis, independent samples T-test and factor analysis were used to find "comprehensive inducing factor" within the whole algae growth cycle. Independent samples T-test was used to check the significant between the results of Q-type hierarchical cluster analysis which gave accurate conclusion about the relation between nutrient factors, physical factors and ecological factors, including 17 indicators of total nitrogen, total phosphorus, nitrogen and phosphorus in the structure of the parameters, rainfall, evaporation, such as transparency and Chl.a, and algae relations growth phase, and finally got the "comprehensive inducing factor" at different growth stages of algae comprehensive through factor analysis method. The results show that hierarchical cluster analysis gave four stages about algae growth, however, independent samples T-test showed that only three groups had a significant difference(p <0.01 or p <0.05). In the final, algae cycle growth phase was divided into three stages: October 2013~January 2014 algae dormant stage, February 2014~June 2014 recovery-rapid propagation of the transitional stage and July 2014~September 2014 rapid Propagation-bloom formation stage. TP, TDN, TDP, TN / TP, DIN / TP and DIN / DIP and other indicators of nutrient became the premier comprehensive induction factor in algae recovery period and rapid growth period. TN were determined to be the third main composition, which was not significant on the growth of algae.During the monitoring period, Tianjin Harbor Ecological Wetland Park reclaimed- water lake was mild-severe eutrophication state. Take Environmental quality standards of surface water as restriction standard, the water quality of it was between class Ⅳ and class Ⅴ.