| The high concentrations of Nitrogen(N) and Phosphorus(P) were usually considered as the cause of algal bloom, and most of studies in algal bloom were focus on the effects of nutrients in algae growth. However, there were some studies pointed out that the concentrations of nutrients in some tributaries in TGR area were higher than the minimum threshold of eutrophication but there was no algal bloom appeared. Infact, each type of nutrients has different forms and only a specific form can be utilized by alage. The other forms of nutrients will be transformed into the specific form when these specific forms are consumed. Enzymes play an important role in this process, and the nutrients utilization capacity of algae is determined by the enzyme activities to some extent.The water environmental problems appeared in Three Gorges Reservoir(TGR) area were always the focus of attention since the Three Gorges project was carried out, especially after Three Gorges Dam(TGD) started operating on water level of 175 m in 2010. As a tributary of Yangtze River in TGR area, urban section of Jialing River was became affected by backwater of TGD, and showed different water environment conditions compared with the previous. Such as slower water velocity, longer pollutants retention time, weaker diffusivity and weaker self-purification capability. These phenomenons resulted in an increased eutrophication. In recent years, the algal blooms appeared in urban section of Jialing River every spring were not only broken the ecological balance but also potentially threaten the drinking water safety of urban area. To solve these problems, it is necessary to make deeply studies in frequent algal blooms in urban section of Jialing River.In this study, urban section of Jialing River was chosen to study the different forms of C(carbon), N, P, and the variations of nutrients concentrations, activities of key enzymes in nutrients utilization, algal density, and other water environment parameters. The relationships between different parameters were studied through correlation analysis, the equations between different parameters were also determined through regression analysis. The monitoring model of enzyme activity and algal cell density for the whole year, the prediction model for risky stage of algal bloom was developed through multivariate linear regression. According to the experiments of raw water, variation ranges of enzyme activites, algal cell density and their related parameters were determined. After that, alkaline phosphatase and Synedra were chosen in experimental simulation water to verify the relationships among enzyme activity, algal cell density and their related parameters in raw water. And further to study the mechanism between enzyme activity and algal growth. Main conclusions are as follows:(1) CAA was lowly positively correlated with T, modestly positively correlated with Zn2+, highly positively correlated with p H and Chla, modestly negatively correlated with DIC, and highly negatively correlated with CO2. Its range from 0.094 EU/106 cells to 1.301 EU/106 cells during the whole year, high in summer and low in winter, had a maximum in April 3. The relationship between CAA and its related parameters is as follows: CAA=0.027Chla+0.052 p H-0.079CO2+1.774Zn2++0.592(R2=0.803, n=15). NRA was modestly positively correlated with p H and Chla, lowly positively correlated with EHP, modestly negatively with SRP, and highly positively correlated with Zn2+. Its range from 0.052 fmol.min-1.cell-1 to 0.280 fmol.min-1.cell-1 during the whole year. NRA in discharging stage was higher than in other periods, and it had a maximum in April 4. The relationship between NRA and its related parameters is as follows: NRA=0.017Chla+0.037 p H-0.246Fe3++0.111NO3--0.267(R2=0.770, n=15). APA was modestly positively correlated with p H and Chla, lowly positively correlated with EHP, modestly negatively correlated with SRP, and highly positively correlated with Zn2+. Its range from 0.442 nmol.min-1.L-1 to 8.679 nmol.min-1.L-1 during the whole year. APP in discharging stage is much more higher than in other periods, and it had a maximum in March 26. The relationship between APA and its related parameters is as follows: APA=60.8Zn2+-8.34EHP+0.21Chla-1.3SRP+0.19 p H-3.02(R2=0.821, n=15). Results of experimental simulation with the use of culture medium showed that secretion of alkaline phosphatase can be induced by orthophosphate with low concentration and different types of organic phosphorus. The relationships between APA and its related parameters(SRP, water temperature, p H, Zn2+) were accord with the rules in raw water.(2) Algal cell density in urban section of Jialing River was range from 1.56×104cells/L to 84.81×104cells/L during the whole year. It was highest in discharging stage and lowest in impounding stage, with a maximum appeared in the discharging stage. The minimum threshold of algal bloom in urban section of Jialing River is 2×105Cells/L. Algal cell density was modestly positively correlated with V, p H, Zn2+, PP, DOP, NRA, and APA, highly positively correlated with Chla and CAA, lowly positively correlated with POC and EHP, modestly negatively correlated with CO2, TDP, and SRP. It had no correlations or correlation was not significant between algal cell density and other parameters. The experiments of experimental simulation showed that the relationships between algal growth and its related parameters were accord with the rules in raw water. Synedra’s optimum temperature is 20- 25℃, optimum p H is 8.5- 9.5, optimum N/P ratio is 5/1- 50/1. A moderate water velocity can improve algal growth, but a high water velocity will inhibit algal growth. Algal growth will be inhibited when the water lack of Zn2+. Synedra has a higher tolerance than microcystis aeruginosa in the water without phosphorus. The utilization capacities of Synedra in different organic phosphorus are SRP>ATP>GP>G6P>LEC, it has a negative correlation with molecular weight. And different concentrations of organic phosphorus between 0.3mg/L to 10mg/L has no significant difference in promotion of algal growth. There is a linear positive correlation between APA and algal cell density in variations of different parameters except N/P.(3) In consideration of nutrients, enzyme activity, algal cell density and other environment parameters, the monitoring model of algal cell density for the whole year in urban section of Jialing River is as follows: Cells =- 1.262 V + 5.152 p H + 8.962Zn2+ + 9.103 Chla + 1.191POC- 4.871CO2- 8.336 SRP + 5.383 EHP + 7.88 NRA + 8.948 APA + 6.807 CAA + 19.6; the monitoring model of algal cell density for the risky stage of algal bloom is as follow: Cells = 156.435V- 3.287CO2- 22.588 CAA + 3.516 APA + 125.881 NRA + 43.916; the prediction model of algal cell density for the risky stage of algal bloom(two weeks in advance) is as follow: Cells =- 46.507 p H + 37.894CAA-586.025 EHP + 2.237 APA + 358.27 NRA + 352.778.A deeper understanding in algal bloom mechanism had been obtained from the enzyme activity perspective, it is also can provide theoretical support in algal bloom monitoring and prediction. |
