The Influences Of Nitrogen,Temperature And Illumination On Interactions Among Daphnia Magna,Ceratophyllum Demersum And Cyclotella Sp.

Water eutrophication has become an increasingly serious environmental problem,and algal bloom of its one of the main manifestations.The high frequency of algae bloom has been great not only to economic loss,but also to ecological harm.Therefore,it has been an urgent environment problem for us to control algae bloom.In freshwater ecosystem,bio-manipulation techniques and large-scale aquatic plant restoration and reconstruction techniques are important means for constructing healthy and stable ecosystems,and their algae-controlling effects are closely related to environmental factors such as nitrogen and phosphorus concentrations,water temperature and light.Thus,the effects of nitrogen phosphorus concentrations,temperature,illumination factors on the control algae of bio-manipulation techniques and large-scale aquatic plant restoration and reconstruction techniques can provide a scientific basis for ecological restoration of water pollution.The main subjects of study for this article are Cyclotella sp.,Daphnia magna,and Ceratophyllum demersum.The paper analyzes the relationship between the influence of D.magna,C.demersum on the control effects of Cyclotella sp.and nitrogen,phosphorus,temperature and light.At the end of the experiment,the growth rate of the subjects and the removal rate of nitrogen and phosphorus in the culture medium were calculated.The main results were as follows.(1)The nitrogen concentrations were set at 0.5,2.0,4.0,8.0,16.0 mg/L,the phosphorus concentration was set 1.5 mg/L,and the light intensity was controlled as 2 600 lx,which gives light-dark cycle ratio(L:D)of 14 h:10 h,with a temperature of 25 ?.(1)When Cyclotella sp.was cultured individually,the growth rate of Cyclotella sp.increased as nitrogen concentrations increased.At the end of the experiment,the cell density of Cyclotella sp.gradually remained relatively stable in the nitrogen concentration levels ranged from 0.5 to 4.0 mg/L,and Cyclotella sp.still continued to grow in the nitrogen concentration levels ranged from 8.0 to 16.0 mg/L.(2)When Cyclotella sp.were co-cultured with D.magna,the growth of the Cyclotella sp.hadsignificantly inhibited at the nitrogen concentration levels of less than 2.0 mg/L.The growth rate of Cyclotella sp.greatly increased as nitrogen concentrations increased at the nitrogen concentration levels of higher than 4.0 mg/L,and the control effect of algae was insignificant.And the growth rate of D.magna was higher significantly than that of Cyclotella sp..(3)When Cyclotella sp.were co-cultured with C.demersum planting water or C.demersum,the growth rate of the Cyclotella sp.was negative,and the growth of the Cyclotella sp.was significantly inhibited in the nitrogen concentration levels of less than 2.0 mg/L.The algae inhibition effect of the allelopathic experiment was significantly lower than that of the co-culture experiment in the nitrogen concentration levels ranged from 0.5 to 16.0 mg/L.The growth of C.demersum at a lower nitrogen concentration(The nitrogen concentration levels ranged from 0.5 to 2.0 mg/L)was significantly better than the medium-high nitrogen concentration(The nitrogen concentration levels ranged from 4.0 to 16.0 mg/L).(4)When Cyclotella sp.were co-cultured with D.magna,C.demersum,the growth of Cyclotella sp.was effectively controlled in the nitrogen concentration levels of less than 16.0 mg/L.In the nitrogen concentration levels ranged from 0.5 to 2.0 mg/L,the growth rate of C.demersum and D.magna were significantly growth positive,while negative increase in Cyclotella sp.,and algae had significantly inhibited.In the water,with the addition of C.demersum and D.magna,the growth of algae had significantly inhibited,the nitrogen and phosphorus content had significantly reduced,and the water quality was significantly improved.(2)The temperature gradients were set at 15 ?,20 ?,25 ?,30 ?,and nitrogen phosphorus concentration gradient was the same as(1),which gives a light intensity of 2 600 lx,with a light-dark cycle ratio(L:D)of 14 h:10 h.At the temperature of 15 ?,the living conditions of Cyclotella sp.,D.magna and C.demersum could not grow well.At the temperature of 20 ?,the survival status of Cyclotella sp.was significantly greater than that of D.magna and C.demersum,and dominated with the algae's inhibition effect of not significant.In the temperature ranged from 25 to 30 ?,or 15 ?,and the nitrogen concentration levels ranged from 0.5 to 4.0 mg/L,the growth rate of Cyclotella sp.was lower than that of D.magna and C.demersum,and the control effect of algae was significant.At this time,the higher was the removal rate ofnitrogen and phosphorus.(3)The light intensities were set at 1 600 lx,2 600 lx,3 600 lx,4 600 lx,and nitrogen phosphorus concentration gradient was the same as(1),which gives a light-dark cycle ratio(L:D)of 14 h:10 h,with a temperature of 25 ?.At the light intensity of 1 600 lx,the living conditions of the three organisms could not grow well.In the light intensity ranged from 2 600 to 3 600 lx,D.magna and C.demersum on the control effect of Cyclotella sp.gradually weakened as light intensity increased.In the light intensity ranged from 2 600 to 4600 lx,and the nitrogen concentration levels ranged from 0.5 to 4.0 mg/L,the growth rate of Cyclotella sp.was lower than that of D.magna and C.demersum,and the control effect of algae was significant.(4)The light-dark cycle ratio(L:D)were set at 10 h:14 h,12 h:12 h,14 h:10 h,16 h:8 h,and nitrogen phosphorus concentration gradient was the same as(1),which gives a light intensity of 2 600 lx,with a temperature of 25 ?.At the light-dark cycle ratio of 10 h:14 h,the living conditions of the three organisms could not grow well.At all the light-dark cycle ratio levels,D.magna and C.demersum on the control effect of Cyclotella sp.gradually weakened as illumination time increased.In the light-dark cycle ratio of 10 h:14 h,12 h:12 h,and the nitrogen concentration levels ranged from 0.5 to 4.0 mg/L,the growth rate of Cyclotella sp.was lower than that of D.magna and C.demersum,and the control effect of algae was significant.While the highest was the removal rate of nitrogen and phosphorus at the light-dark cycle ratio of 16 h:8 h.