| Cyanobacteria salvage not only is a kind of useful emergency measures for controlling cyanobacterial bloom, but also can effectively reduce the load of nitrogen and phosphorus in water. The density restriction is one of population competition effects, and the growth of algae is affected by the density restriction. However, there is still no systemic study for whether the artificial salvage in the breakout of water bloom can get rid of the restrain effect of density dependant on the algae growth. In order to better understand the effect of algae salvage on the water blooms, the field mesocosm experiment in situ and the indoor simulation experiment was created. In this article, we analysed the algae salvage on the reduction load of nitrogen and phosphorus in water, and discussed the dynamic changes of the algae growth and community structure after salvage. The results of this study could probably provide reference for control the water bloom. The main results were summarized as follows:1. Algae salvage can effectively reduce the load of nitrogen and phosphorus and the endogenous accumulation. Different salvage strength and salvage frequency have different effects on the change in the concentration of the nitrogen and phosphorus. The removal of nitrogen and phosphorus increased with the increasing of the salvage strength. After the80%and60%algal biomass was salvaged from the experimental system, the algal biomass slowly began to rise at the10th day, but it didn’t result in the breakout of water bloom again. And the dissolved nitrogen and phosphorus gradually began to reduce. The more often the salvage frequency, the higher the removal of N and P would be. The higher salvage frequency (1day time and2days time) promoted the algal growth, so the content of chlorophyll-a(Chl.a) began to rise at the10th day, and the dissolved nitrogen and phosphorus also gradually began to decrease. Therefore, the two strength of80%and60%,together with the two salvage frequency of1day time and2days time, can be used as the effective parameter during the salvaging operation.2. The alage salvage in different growth stages made significantly different impact on the epitaxial growth of Microcystis aeruginosa(p<0.01). In the logarithmic phase treatment, Microcystis aeruginosa still could grow well for later events, and with the increase of the intensity on alage salvage, the time of entering exponential phase of growth and period of stationary phase could be lengthened, and the maximum population density could be heightened. In the stationary phase experiment, Microcystis aeruginosa went dormant immediately following, and alage was inhibited from growing. In addition, the accumulated contents of malondialdehyde (MDA) and the activities superoxide dismutase (SOD) of Microcystis aeruginosa showed that alage salvage eliminated the density-dependent during the process of growth, and the aging time of the algae was lengthened.3. Algae salvage can effectively reduce the total phytoplankton cells in the water, especially the blue-green algae. At the same time, it also could improve the growth of other species, such as green algae, diatom, Cryptophyta, and so on. The kinds of the phytoplankton in the salvage enclosure changed drastically over time, from7kinds in early stage increasing to the22kinds at the end of the experiment. And the cell abundance proportion of the green algae,diatoms, hidden algae, etc. increased from the start of1.88percent to43.02percent in the end. Algae salvage can be a valid path to improve species diversity of the phytoplankton in the experimental enclosure, with the composition of the algae switching from oneness to diversity. The results showed that algae salvage can significantly control the explosive growth of the blue-green algae, so that it took part in a very important position on the stability of the algae community structure. |
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