Effect Of Dissolved Organic Nitrogen And Phosphorus On Algal Growth In The Landscape Water Of Low Nutrient Level

Pollution from exogenous runoff and release of endogenous sediments contributes to the eutrophication landscape waters,and the accompanying water blooms can lead to the function degradation of water ecosystem.However,few studies have reported the effects of organic nitrogen and phosphorus on algal growth at present.Therefore,the paper firstly investigated the changes of conventional water quality indexes,biological indexes and organic matter indexes in different water zones of the moat of Xi’an with different water sources.Based on the comparative studies,the interaction patterns between organic nutrients and algae were studied in different water zones.Then,the release contribution of endogenous sediment to the organic nutrients of overlying water was tested through static experiment.Finally,the effects of organic matter originated from the algal under methods,as well as the organic nitrogen and organic phosphorus of different concentrations and ratios,on the growth of Microcystis aeruginosa were investigated in the laboratory.The above studies can provide an important basis for the management of eutrophication and control of algae in landscape water bodies.The main results and conclusions of the study were obtained as follows:1)The water quality monitoring in the moat of Xi’an for 8 months showed that the water quality in different water zones was at low nutrient level.The organic nitrogen accounted for a certain proportion of the total nitrogen.Meanwhile,phosphorus was dominated by organic phosphorus,and dissolved organic nitrogen accounted for 13.02%,13.30%and 9.67%of the total nitrogen concentration in the recharged zones of surface water,the mixed surface water and reclaimed water,and reclaimed water,respectively.Dissolved organic phosphorus accounted for 60%,25%and 20%of the total phosphorus,respectively.The mean concentrations of algal density and Chl-a in the recharged zone of reclaimed water were higher than those in the surface water and mixed water and surface water.In addition,the Pearson analysis showed that organic nitrogen and organic phosphorus can also affect the growth of algae in addition to inorganic nutrients in landscape water bodies.Therefore,the attention should be paid to the indicators of organic nutrients in water bodies.2)Through the study of static release of sediment from different water recharge areas,it can be seen that the release fluxes of dissolved organic nitrogen from sediment in surface water recharge areas and sediment in reclaimed water recharge areas were 3.60mg/(m~2·d)and 4.54 mg/(m~2·d),accounting for 31.09%and 30.49%of the total nitrogen release fluxes,respectively.Meanwhile the release fluxes of dissolved organic phosphorus were 0.03 mg/(m~2·d)and 0.02 mg/(m~2·d),both accounting for 3.84%of the total phosphorus release flux.This indicated a greater potential for organic matter release from sediments in the reclaimed water recharge area.3)The experimental study on the effects of organic nitrogen and phosphorus from the algal on the growth of Microcystis aeruginosa showed that organic matter from algal could promote the growth of Microcystis aeruginosa,and the bioavailability of produced organic matter from algal under different treatment methods was different.The bioavailability of organic nitrogen produced by natural decay sedimentation and ultrasonic fragmentation were 35.19%and 51.67%,respectively.On the contrary,the bioavailability of organic phosphorus by decaying naturally and ultrasonic fragmentation were 60.00%and 85.00%,respectively.Therefore,the attention should be paid to the positive feedback of organic nitrogen and phosphorus on the growth of algae in the process of using ultrasound to control algae.4)The experimental study on the effects of organic nitrogen and phosphorus on the growth of Microcystis aeruginosa showed that the addition of organic nitrogen and organic phosphorus with different ratios and concentrations could accelerate and maintain the growth of Microcystis aeruginosa under the conditions of low nutrient landscape water,and the higher the concentration of organic nitrogen and organic phosphorus,the better the growth of algae,the higher the DHA activity and the lower the SOD activity.In addition,it was found that Microcystis aeruginosa utilized ammonia nitrogen and phosphate preferentially before organic nitrogen and organic phosphorus in the growth process,while the utilization of organic nitrogen and organic phosphorus by the algae briefly increased the concentration of ammonia nitrogen and phosphate in the water column.