Study Of Physicochemical Properties Of Microenvironment In Cyanobacterial Granules And Water Layer And Their Influencing Factors

Lake eutrophication has become a major water environmental problem in China and all over the world,which has been paid more and more attention in the past three decades.Lake eutrophication can lead to the proliferation of cyanobacteria and form visible blooms.Understanding the mechanism of cyanobacterial bloom formation is significant for us to control cyanobacterial bloom.The field cyanobacterial granules and water body with cynobacterial bloom were selected as the experimental material and the field conditions were simulated in the laboratory.Microelectrodes were used to investigate the microenvironment within cyanobacterial granules and water body with cyanobacterial bloom.The influence of environmental condition on the microenvironment were also studied within the granules and water body.(1)Illumination and temperature are the key environmental factors which influenced the physical properties within the granules.The DO production within the granules increased with increasing illumination and it decreased when the illumination was over high.The pH also increased with the increasing illumination and the Eh had an inverse trend.The maximal DO production occurred at 20?.The net photosynehtsis decreased when the temperature increased to 30?.The varation of pH was similar to that of the DO production.The DO and pH in the granules decreased immediately when the light was turned off.The quick response of the granules to the variations of external environment should be one of the most important mechanisms for the cyanobacteria to be the dominant bloom-forming species.(2)Illumination and temperature also influenced the physichemical properties in the water body with cyanobacterial bloom.The DO production increased with increasing illumination and it decreased when the illumination was over high.pH could achieve 10.5 unde the light condition.Eh decreased with increasing illumination.The DO and pH at the bloom surface increased immediately when the illumination increased,nevertheless,they decreased gradually under the water.The DO decreased to 0 at 3 cm beneath the water when the temperature increased to 30?.The DO level in the high-density cyanobacterial bloom was lower than that in the low-density cyanobacterial bloom.When the cyanobacterial bloom ourbreak,a large number of cyanobacteria accumulate at the water surface which decreased the DO level under the water,and high temperature aggregavate such progress.High temperature combined with anaerobic condition aggregavated the ourburst of cyanobacterial bloom and resulted in feculent water aggregation.(3)In addition to illumination and temperature,pH was another important factor which could influence the growth of cyanobacteria.The photosynthesis of cyanobacteria was inhibited when the environmental pH was over high or over low.The most dynamic photosynthesis in the granules was achieved at external pH 9.The difference of pH was about 2.5-3.0 at external pH 6-8,and it decreased to 1.0 and 0.5 when the external pH increased to 9 and 10.The initial pH in the experimental cyanobacterial bloom decreased from 10 to 9 after incubated in the dark overnight.The maximal pH in the water was 10.0-10.5 in the light.The growth and photosynthesis of cyanobacteria was controlled by both of the internal and external pH.The growth of cyanobacteria was inhibited at high environmental pH condition,which shoud be one of the most important self-regulation mechanisms of cyanobacteria.(4)DO,sality and redox potential in the water could also influence the growth of cyanobacteria.Anaerobic environment inhibited the photosynthesis of cyanobacteria and the most dynamic photosynthesis was achieved when the DO level in the water was 100?mol L-1.Photosynthesis was inhibited when the environmental DO level was over high.The maximum DO level in the granules increased with increasing external DO level.It may be the result of co-action of photosynthesis of cyanbacteria and oxygen diffusion.When the oxygen concentration in the water is supersaturated due to cyanobacterial photosynthesis,supersaturated oxygen level should inhibit the photosynthesis of cyanobacteria.Supersaturated oxygen inside and outside the cyanobacterial granules could provide additional buoyancy for the granules.The photosynthesis of cyanobacterial granules decreased with increasing saltnity.It may be due to alteration of osmolality in the cell membrane and the reduction of photorepair of photosystem.Appropriate decrease of redox potential did not have a significant impact on the photosynthesis of cyanobacteria while the photosynthesis would be inhibited when the redox potential continued to decrease.(5)The oxygen production within the cyanobacterial granules had a positive correlation with the size of cyanobacterial granules.The photosynthesis in the granules of small size was inhibited in the high light.The floating rate of large granules had an inverse correlation with illumination intensity while the floating rate of small granules fluctuated with illumination intensity.The oxygen concentration within the intracelluer space increased with increasing illumination.The floating rate of the granules with loose structer was larger than that of the granules with dense structer.It might due to more intracellular spaces exsited in the granules with loose structer;therefore,oxygen could fille the space and provided additional buoyancy for the granules.The buoyancy regulation of the small granules is more flexible than the large granules.Therefore,the cyanobacteria always existed in the granules'morphology of small size and loose structer in the field,and that may be one of the most important reasons for the cyanobacteria become the dominant bloom-forming species.