Study On The Influence Of Submerged Macrophytes On The Growth Characteristics Of Microalgae In Reclamed Water

Since the 1930s,the ubiquitous global eutrophication and water blooms have exacerbated the water crisis,the recycling of sewage is the best way to solve the shortage of water resources and complete the natural restoration of water ecological cycle,but the problem of water bloom is the main problem in the process of recycling.As a pioneer species in the restoration of aquatic ecological environment,submerged plants can effectively inhibit the growth of microalgae,which is the key link to the problem of water bloom.Therefore,it is important to study the effects of submerged plants on the growth characteristics of microalgae in the reclaimed water.In this paper,seven common submerged macrophytes such as Vallisneria natans.Potamogeton crispus,Ceratophyllum,Myriophyllum spicathum,Hydrilla verticillata,Elodea nuttallii and Myriophyllum aquaticum were selected,and the mixed bloom-forming microalgae was used as the treatment object to study their growth characteristics on the macrophytes under the actual effluent conditions from sewage treatment plant.Through redundancy analysis,the limiting factors of algal inhibition in different plants were identified,and then two submerged plants with better algal inhibition effects were screened,and algae inhibition experiments with different planting densities were carried out.According to the growth characteristics of microalgae and the relative growth index of plants,the inhibitory effects of different planting densities on microalgae were compared,combined with the response surface model to further obtain the optimal combination ratio of Hydrilla verticillata and Myriophyllum spicatum.The results of this study can provide theoretical guidance for the use of submerged macrophytes to control blooms.The main results are summarized as follows:(1)Hydrilla verticillata,Myriophyllum spicatum and Ceratophyllum showed strong algae-inhibiting effects on the K,Rmax,and ?.Myriophyllum spicatum and Ceratophyllum had the best inhibitory effect on cyanobacteria community.Redundancy analysis shows that the competition of nutrients by plants and the DOM secreted by plants are the main limiting factors for algae inhibition,and the limiting effect of nutrients is stronger.Hydrilla verticillata and Myriophyllum spicatum have the strongest inhibitory effect on the nutrient absorption capacity of algae cells,the inhibition rate of total phosphorus uptake reached 90.6%and 75.04%,respectively,and the inhibition rate of total nitrogen uptake was 67.36%and 54.59%.respectively.There were many kinds of dissolved organic matter related to the inhibition of algae in the group of Myriophyllum spicatum and Ceratophyllum,and the content of dissolved organic matter related to the inhibition of algae secreted by Myriophyllum spicatum was the highest.In summary,Hydrilla verticillata and Myriophyllum spicatum are the most suitable algae-inhibiting pioneer plants for landscape reuse of reclaimed water.(2)Under the conditions of planting density greater than 10 g/L,Hydrilla verticillata and Myriophyllum spicatum could maintain good algae-inhibiting effect on microalgae biomass and growth rate,the inhibition rate of the maximum biomass of microalgae reached 70%,and the inhibition rate of the maximum population growth rate of microalgae reached 75%.The plant growth indexes of Hydrilla verticillata and Myriophyllum spicatum reached the optimal values under the conditions of 15 g/L and 10 g/L planting density,respectively.The relative growth amounts were 75.17%and 46.67%.In summary,the planting density of 10 g/L and 15 g/L is the best combination density.(3)The inhibition rate of Hydrilla verticillata-Myriophyllum spicatum on microalgae was significantly higher than that of single submerged plant.The quadratic polynomial model established by the response surface method can evaluate the effects of the planting density of Hydrilla verticillata and Myriophyllum spicatum on the biomass inhibition rate of microalgae and the relative growth of plants.Under the combined cultivation conditions of 0.79 kg/m2 Hydrilla verticillata and 0.87 kg/m2 Myriophyllum spicatum,the inhibition effect on the microalgae was the best,and the maximum biomass inhibition rate reached 93.42%.Moreover,under the combined planting conditions,the growth of the two plants did not interfere with each other,and the relative growth of the plants of Hydrilla verticillata and Myriophyllum spicatum remained at 84.19%and 44.57%,respectively.Under the optimal combination,it is recommended to harvest 17%-36%of the total biomass of Hydrilla verticilla and 10%to 23%of the total biomass of Myriophyllum spicatum every 7-20 days.