Research On Eutrophication Threshold And Limiting Factors In Miyun Reservoir

Lake and reservoir are important surface water resources and significant part of the ecological environment.Excessive inflow of Nitrogen and Phosphorus nutrients leads to rapid and wild growth of algae,which causes a series of eutrophication phenomena while gathering on the surface of the water,like water transparency decline and water quality deterioration,etc.They have become one of the important water environment problems which influences the survival and development of human being.Miyun Reservoir,the main surface water resource of Beijing urban domestic water,has got widespread attention from all sectors of the society,for it functions as the most important surface drinking water source of Beijing,the capital city of China.Due to sharp decline of water storage in recent years,partial area of the reservoir has appeared the symptoms of eutrophication.Polluted emission inflow and eutrophication tendency are threatening the water supply security to some extent.Water bloom prevention and treatment and healthy water ecology construction still have a long way to go.As the South-to-North water transfer project completed,the structure of algae species will also bring to new impact on the water quality of Miyun Reservoir.Through field detection,indoor and original site experiments towards water body from the Miyun Reservoir,this research studies the required threshold of nitrogen and phosphorus of the growth of algae in Miyun Reservoir,the impact on the growth of algae owing to different concentration of nitrogen and phosphorus,and the impact on the growth of algae owing to structure of algae species.Finally,the researcher draws some conclusion as following:(1)The study on eutrophication threshold of of Miyun Reservoir.Through analysis the water quality index of Miyun Reservoir,there is spatial heterogeneity on the nitrogen and phosphorus concentration.The sampling point of Bai river shows that the storage place of phosphorus concentration is relatively high.The sampling point of Chao river shows that the storage place of nitrogen concentration is relatively high.As the distance from the storage places,the corresponding of the nitrogen and phosphorus concentration changes.According to the field detection data collected from Miyun Reservoir from April,2015 to November,2015,expect for June and July,49.7%of the total phosphrous is algae available phosphrous and 52.79%of the total nitrogen is the algae available nitrogen.Indoor experiment shows that the growth rate grows fastest when the phosphates concentration is between 0.03mg L-1 and 0.04mg L-1,if nitrogen is abundant enough.However,the growth rate grows slowly when the phosphates concentration is more than 0.04mg·L-1.While under the condition that phosphrous is enough and the nitrogen density is between 0.1mg·L-1 and 0.3mg L-1,the growth rate also grows fastest.However,the growth rate grows slowly when the nitrogen density is more than 0.04mg L-1.Therefore,indoor experiment shows that the threshold of nitrogen and total phosphrous are 0.3mg·L-1 and 0.04mg·L-1 respectively.The threshold of eutrophication of Miyun Reservoir can be figured out according to the ratio of algae available phosphrous in total phosphrous and algae available nitrogen in total nitrogen,as well as the results of indoor algae growth simulation experiment.The research indicates that the threshold of total nitrogen and total phosphrous are 0.57mg-L-1 and 0.08mg L-1 respectively.(2)Impact of nitrogen concentration and phosphrous concentration on the growth of algae in Miyun Reservoir.The researcher selects ammonium nitrogen and nitrate nitrogen as the nitrogen source respectively and sets different nitrogen and phosphrous concentration,in order to learn the the growth and proliferation rule of algae in Miyun Reservoir and earn a better knowledge of the relationship between eutrophication and nutrients,like nitrogen,phosphrous,etc.Under different nitrogen source,algae shows better growth in the nutriment of nitrate nitrogen than that of ammonium nitrogen and above all.Under the ammonium nitrogen source,the content of chlorophyll a in algae is increasing due to the increase of nitrogen concentration.Under the nitrate nitrogen source,the growth of algae is also different.Under the condition of different nitrogen concentration,chlorophyll a in algae is increasing due to the increase of nitrogen concentration in general and algae grows relatively great when the nitrate nitrogen concentration is 0.5mg·L-1.Under the condition of different phosphrous concentration,algae grows best under the situation when nitrogen concentration is 0mg·L-1 and phosphrous concentration is 0.02mg L-1,when ammonium nitrogen concentration is l0mg.L-1 and phosphrous concentration is 2mg.L-1,or when the nitrate nitrogen concentration is 10mg.L-1 and the phosphrous concentration is 0.5mg L-1.Under the condition of different concentration of nitrogen,the growth of algae is also different,which indicates that the concentration of nitrogen restricts the growth of algae.(3)Impact of different phosphrous concentration and water body on algae species and the growth of algae.Taking water body in Miyun Reservoir and that of the "South Water" in South-to-North WaterDivision Project as the research objects,the researcher mixes the water body by different ration and adds different concentration of phosphrous to conduct the original site experiments in Miyun Reservoir.In class A water body(volume ration of South Water and water body in Miyun Reservoir is 1:9),the percentage of diatom increases prominently,while the general percentage of chlorophyta and cyanophyta decreases.When the phosphrous concentration is Omg ·L-1,the percentage of diatom increases to the maximum value.When the phosphrous concentration is 0.01,0.02 or0.03mg L-1,pyrroptataappears in the water body.Euglenophyta's percentage of diatom increases prominently when phosphrous concentration is 0.01,while cryptophyta's percentage of diatom increases prominently when phosphrous concentration is 0.04mg.L-1.In class B water body(volume ration of South Water and water body in Miyun Reservoir is 3:7),when phosphrous concentration is 0,0.01 or 0.03mg L-1,pyrroptata's percentage of diatom increases prominently.Cryptophyta's percentage of diatom increases prominently when phosphrous concentration is 0.02 or 0.03mg L-1,while euglenophyta's percentage of diatom increases prominently when phosphrous concentration is 0.02mg L-1.In class C water body(volume ration of South Water and water body in Miyun Reservoir is 5:5),chrysophyta's percentage of diatom increases prominently when phosphrous concentration is Omg·L-1 and pyrroptata's percentage of diatom increases prominently when phosphrous concentration is 0.01mg L-1.Cryptophyta's percentage of diatom increases prominently in the water body when phosphrous concentration is 0.03 or 0.04mg L-1,.In class D water body(volume ration of South Water and water body in Miyun Reservoir is 9:1),pyrroptata's percentage of diatom increases prominently when phosphrous concentration is 0.01 or 0.02mg L-1,while cryptophyta's percentage of diatom increases prominently when phosphrous concentration is 0.02 or 0.04mg·L-1.Under the condition of different concentration of phosphrous,the structure of algae species is different.Study shows that the structure of algae species which influenced by the increase of phosphrous concentration,but chlorophyta,cyanophyta and diatom are also the dominant algae species.Study also indicates that the growth of algae which influenced by change of structure of algae species.