| With the high-speed development of economy and the acceleration of urbanization, water resources are shortages in our country, and are gradually in short supply. Meanwhile we are also faced with the rising river basin water pollution problems. The requirement of source water reservoir quality is higher than the general sense of lakes and reservoirs, which impacted the drinking water problems, so it is more difficult to control water pollution. In recent years, many reservoirs in China are faced with varying degrees of water pollution problems and the phenomenon of eutrophication. Zhoucun is a water supply source of Zaozhuang City and belongs to a provincial key medium reservoir. Because of a lot of fish cage culture, water pollution is serious and the reservoir has serious water eutrophication. In order to improve the quality of city supply water in the short term, the mixing technology will be applied to control algae growth near the water intake. Therefore, the research of the growth and decay of algae under the hybrid stress conditions has certain directive significance to control algae by mixing technology and provides the technical basis.Algae in Zhoucun reservoir was studied on the distribution of algae in natural conditions and the growth and decay under the stress of the different water depth conditions with different light, temperature and pressure through laboratory and field experiment. The main conclusions are as follows:(1) The Zhoucun reservoir water transparency was generally between95and100cm. The sunlight in reservoir surface water was strong, and the light intensity in0-4m water depth declined exponentially with the increase of water depth. At12:00, the light intensity in0.5m water depth reached850001x, in water depth below4m the light intensity was less than10001x and in water depth below6m there was no light intensity. The surface temperature was higher, which was between25and30℃in summer, the temperature in water depth below14m was constant at about14℃. The dissolved oxygen in reservoir surface water was higher and generally at about14mg/L, it was less than10mg/L in water depth below4m, and in water depth below6m the dissolved oxygen was almost Omg/L.(2) Algae in Zhoucun reservoir was mainly dominated by cyanobacteria, accounting for about80%of the total number of algae, the proportion of green algae and diatom was similar. Lyngbya was the majority of cyanobacteria, green algae mainly included Planktosphaeria gelatinosa, Chlorocoecum nifusionum and Nephrocytium sp., while Cyclotella and Synedra was the majority of diatom. Lyngbya, Planktosphaeria gelatinosa, Synedra was the majority of algae in water depth above4m, which respectively accounting for about80%,11%and8%of the total number of algae. In water depth below7m the proportion of cyanobacteria was reduced to58%, while the proportion of green algae and diatom was increased to25%and17%. The number of algae in reservoir was more in4m water depth under nature conditions, which chlorophyll concentration was between22and30μg/L. The algae concentration reached maximum in2m water depth where was about2times transparency. The algae concentration was reduced sharply between4and6m depth, and chlorophyll concentration was10μg/L below the depth.(3) The fluorescence determination method was explored and determined, which was used to determine the activity of algae. The algae cells were stained by FDA with producing fluorescence and used fluorescence spectrophotometer to measure the absorbance. The color process and fluorescence intensity were increased with time, the equilibrium process was very long. Selected30min as the reaction time and measured the relative standard deviation of2.52%, which showed a better repeatability. Fluorescence value increased linearly with temperature between18-27℃, and over27℃the increasing amplitude of fluorescence value decreased. The relative standard deviation of18℃,21℃,24℃,27℃,30℃and33℃respectively was6.58%,4.60%,4.27%,3.46%,2.39%and2.48%. Eventually the reaction time was determined for30min and the reaction temperature was30℃. The fluorescent value had a good linear relationship with the algae chlorophyll concentration which was measured by this method. It could be used to determine the relative activity of algae.(4) The algae production rate reached maximum at325001x, which was18.5mgO2/(mgChl-a·h), and was reduced whether increasing or decreasing the intensity. The algae production rate was-2.2mgO2/(mgChl-a·h) at zero intensity. The cell activity increase rate was2.0308h-1at325001x, which was the maximum, and was decreased at other intensity. The cell activity increase rate was-1.049h-1at zero intensity. The results showed that the algae photosynthesis was largest and the cell activity was highest at325001x. At zero intensity algae couldn’t release oxygen for photosynthesis and the cell activity weakened, algae would decay with the increasing of incubation time.(5) Algae was all growing under15～30℃. The algae production rate reached maximum at 26℃, which was18.5mgO2/(mgChl-a·h),and was reduced whether increasing or decreasing the temperature. The algae production rate was12.5mgO2/(mgChl-a·h)at15℃, and was13.2mgO2/(mgChl-a·h)at30℃. The cell activity increase rate was2.0308h-1at26℃, which was the maximum, and was decreased at other temperature. The cell activity increase rate was0.9631h’1at15℃, reducing52%compared with that at26℃.The results showed that the suitable temperature for algae growth was26℃.(6) The algae production rate was maximum at atmospheric pressure, which was18.5mgO2/(mgChl-a·h)and was reduced linearly with increasing pressure. The algae production rate was9.3mgO2/(mgChl-a·h),at0.3MPa, reducing50%. The cell activity increase rate decreased with increasing pressure, the cell activity increase rate was1.2646h-1at0.2MPa and was-0.3432h’1at0.3MPa. The algae photosynthesis was larger and the cell activity was higher within0.2MPa. At0.3MPa algae could release oxygen for photosynthesis, but the cell activity weakened, algae would decay with the increasing of incubation time. The results showed that when algae have certain light and temperature, the growth of algae was inhibited by the increasing pressure.(7) The total production of algae photosynthesis was reduced linearly with increasing water depth in water depth above6m, and tended to zero in water depth below6m. Algal respiration was larger in water depth above6m, reduced in water depth below6m, and kept constant in water depth below12m. The compensation point of algae was between2.2and3m, the growth of algae in water depth above compensation point was net growth, and was negative in water depth below compensation point, the maximal negative growth was in6m water depth, where the production was about-63.17～-43.66mgO2/(mgChl-a·h), and the negative growth decreased in water depth below12m,where the production was about -26mgO2/(mgChl-a·hb).When the mixing upper and lower water layer technology was applied to control algae, the minimum mixing depth must be above7m. |
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