Stress Factors Of Algae And Utilization Of Nitrogen And Phosphorus In Coastal Constructed Wetland

As a kind of ubiquitous microorganism in wetland,microalgae has the ability to absorb and utilize nitrogen and phosphorus.It is also an undertaker of self-purification function in wetlands.Among the different types of constructed wetlands,the costal constructed wetlands have the characteristics of variable salinity conditions and unitary structure between aquatic plants and microorganisms.This paper takes Tianjin Binhai New District costal constructed wetland park as an example.The effects of salinity and allelochemical 2-methylacetoacetate(EMA,C7H12O3)which derived from dominant plant Phragmites Australis to the growth,antioxidant enzyme activity and peroxide products,nitrogen and phosphorus absorption and utilization capacity of Chlorella vulgaris and Chlorella pyrenoidosa in the wetland were researched.(1)The results under different salinities show that the growth of two species chlorella can be stressed by salinities higher than 0.5%,while the growth of two species chlorella under the 0.5%salinity is promoted.After the 10 d experiment,the cell density was 16.59 and 11.52 times of the initial density under 0.5%sailnity.Chlorella vulgaris is more sensitive to salinity changes compared to Chlorella pyrenoidosa.By monitoring pH and oxidation-reduction potential(ORP),it was found that algae are more prone to acidification and hypoxia in the medium under saline conditions,which led to deterioration of water quality.Salinity also stimulates an increase of intracellular Malondialdehyde(MDA)content.And the activity of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)in algae with salinity change obviously.Under the 0.5%salinity,it was beneficial to the absorption and utilization of ammonia nitrogen and the removal of total nitrogen by Chlorella.The 10 d ammonia-nitrogen utilization rates were 36.3%and 49.5%,and the total nitrogen removal rates were 32.8%and 52.1%,respectively.Salinity rise inhibits the uptake of nitrogen and phosphorus by algae.(2)The results of algae cultured under different concentration of EMA show that the growth of Chlorella vulgaris was not inhibited by the stress of EMA,even the growth of Chlorella vulgaris was promoted at 0.1 mg/L concentration of EMA.The increased concentration of EMA would lead to acidification and hypoxia of the pH and ORP in the experimental group lower than that in the control group leading to worsen the water quality.Allelochemicals can effectively promote the absorption and utilization of ammonia-nitrogen by two algaes.The best absorption rate in the experimental group is 1.1 mg/L EMA concentration,at which the utilization rates of ammonia-nitrogen were 53.21%and 60.94%respectively in 9 d.But under the condition of 0.1 mg/L concentration of allelochemicals,Which was the best condition for TN removal.The removal rates were 45.44%and 58.80%respectively in 9 d.Concentration rise of Allelochemicals also inhibit the uptake and utilization of phosphorus by algae.(3)The results of combined condition stress experiments on algae showed that salinity could enlarge the threshold of promoting effect by EMA concentration on Chlorella vulgaris.Salinity and allelopathy have synergistic effects on the inhibition of Chlorella pyrenoidosa.With the increase of salinity and EMA concentration,the effects of the two conditions on the absorption of ammonia-nitrogen by algae were antagonistic to each other.The combined effect of salinity and EMA can further improve the removal ability of total nitrogen by algae compared with the single action.The experimental results also showed that with the increase of salinity and EMA stress,the transformation of nitrogen element by algae increased,resulting in the increase of nitrate nitrogen content in water environment.The effect of salinity and EMA concentration on the absorption of phosphorus by algae was synergistic.