Effects Of Different Nutrient Disturbances On Phytoplankton Community Structure

Since the Three Gorges Reservoir generated power from the impounded power generation,most of the tributaries have occurred in varying degrees of blooms,and research on the prevention and control of blooms has become a hot topic for scholars.From the perspective of biodiversity,algae blooms are actually a phenomenon in which some“harmful”algae grow up to be absolutely dominant.The essence is that the diversity of phytoplankton is reduced and the ecosystem is seriously out of balance.Therefore,increasing the diversity of phytoplankton can promote ecological balance and effectively prevent and control blooms.In order to explore the ecological scheduling mechanism of the Three Gorges Reservoir,on the basis of previous research of this team,ten typical dominant algae were selected to study the competition mechanism and succession pattern of phytoplankton mixed culture under different nutrient disturbance conditions based on indoor control experiments to establish nutrient salt concentrations(The relationship between nitrogen and phosphorus and phytoplankton biomass,community structure diversity index,proposed a suitable disturbance mode and threshold range.Provide basic data for the formulation of the Three Gorges Reservoir Ecological Dispatch Plan and provide a theoretical basis for the Three Gorges Reservoir Ecological Dispatch Mechanism.Based on the previous research results of water temperature,light and nutrient pre-experiment on phytoplankton community structure,the effects of nitrogen and phosphorus nutrients under steady state conditions and pulsed addition of nitrogen and phosphorus nutrients under unsteady conditions on the phytoplankton community structure were studied.A habitat disturbance model that can simultaneously maintain the diversity of phytoplankton and effectively reduce its biomass.Through the study,we mainly get the following understanding:（1）Effects of nitrogen nutrient on algae community structure under steady state conditionsUnder steady-state conditions,when the nitrogen nutrient concentration was 2.214mg·L^-1,the biomass was low and the diversity of algae was the largest,which was due to the suitable growth of algae.At the concentration of 4.871 mg·L^-1,the biomass of algae was the highest and the community diversity was also high.It was the concentration of nitrogen nutrients not suitable for algae growth.The succession pattern of the dominant algae function group is basically:L_M/L_O/X1→L_M/X1 or L_M/L_O.In the middle of the experimental period,algae coexisted in various growth strategies in various experimental groups,and the number of algae in the R-type strategy increased significantly.At the end of the experiment,the community structure was dominated by a competitive C strategy algae,and the community was dominated by a single species（Chlorella）.（2）Effect of pulsed addition of nitrogen nutrient on algae community structureIn the experimental phase of pulsed addition of nitrogen nutrient,its biomass was significantly lower than that of the steady state,while at the same time The pattern is higher than the diversity of the steady state stage.Δ8d is a suitable nitrogen nutrient pulse addition cycle,when biomass is low,and diversity is maximized.In theΔ1d experimental group,the algal growth was the slowest and the diversity was the lowest.It was a period of pulse addition of nitrogen nutrients not suitable for algae growth.The succession rules of the dominant functional group were basically;the succession rule of theΔ1d,Δ2d,andΔ10d experimental groups was L_M/L_O/X1→L_M/X1,and the succession rule of theΔ4d andΔ8d was L_M/L_O/X1/G→L_M/X1/Lo.In the middle stage of the experiment,algae coexisted in a variety of growth strategies in various disturbance groups.The amount of algae in the R-type strategy was significantly reduced,and the C-type strategy algae showed an increasing trend.At the end of the experiment,algal blooms appeared in the disturbance-tolerant S-strategy of the community structure,and the proportion of algae in the competitive C-strategy decreased.（3）Effects of Phosphorus Nutrients on Algae Community Structure under Steady-state ConditionsAt the experimental stage,each experimental group was dominated by chlorella or chlorella coexisted with microcystis.At the end of the experiment,the proportion of 0.0024,0.0072,and 0.0192 mg·L^-1 Chlorella was between 50-60%,reaching the eutrophic phosphorus concentration in the experimental group(P>0.02 mg·L^-1)Chlorella.The proportion of more than 70%.On the time scale,as the concentration of phosphorus nutrients rises,when the phosphorus nutrient is at a higher concentration,it is not affected by its concentration.At the concentration of 0.0384 mg·L^-1,it was the optimum experimental group for algae growth.At this time,the biomass was lower and the diversity was the largest.The succession rules of the dominant functional group were basically:L_M/L_O/X1→L_M/X1 or X1.At the end of the experiment,the experimental group was0.0024 mg·L^-1,0.0072,and 0.0192 mg·L^-1,6.643 mg·L^-1.The main functional group combination X1/L_M is formed,and the functional groups of the remaining disturbance groups are similar in composition,with X1 as the main component group.In the middle period after the disturbance occurred,algae coexisted in various growth strategies in various experimental groups,and the number of algae in the R-type strategy increased significantly.At the end of the experiment,the community structure was dominated by the competitive C strategy algae.（4）Effect of Pulsed Addition of Phosphorus Nutrient on Algal Community StructureIn the experimental phase of pulsed addition of phosphorus nutrients,the biomass was significantly lower than that of the steady-state phosphorus nutrient salt phase.The amount,while diversity is higher than the steady-state phosphorus nutrient salt stage.Δ8d is the suitable nitrogen nutrient perturbation cycle,when the biomass is low,and the diversity reaches its maximum.The succession rules of the dominant functional group are basically:L_M/L_O/X1/H1/G/B/P/D→L_M/X1/L_O/G or L_M/X1/L_O.At the end of the experiment,the experimental groupΔ4d andΔ8d groups The main functional group combination L_M/X1/L_O/G is formed,and the functional groups of the remaining disturbance groups are similar in composition,with L_M/X1/L_O as the main component.In the middle of the experimental period,algae coexisted in various growth strategies in various experimental groups,and the number of S-type algae increased significantly.At the end of the experiment,the community structure was dominated by tolerant S-strategy algae.