Research On Characteristics Of Gas Release From Eutrophication Natural Water

In recent years,human activities resulting eutrophication and water shortage have become a major problem threatening the survival and development of human beings.Eutrophication not only destroy the balance of water ecosystems,but the greenhouse gases releasing from water into the atmosphere is getting increased gradually.Eutrophic lake ecosystem has become the main source of emissions of greenhouse gases.The main purpose of this research is to explore the relationship between characteristics of gases naturally released in water and environmental factors.By monitoring the characteristics of urban serious eutrophication sewage pond in Jiangsu Academy of Agriculture Science(JAAS)in the long-term and the law of gases releasing from water purified by microorganisms-plant joint and water body(sewage pond and Taihu lake)with different environmental conditions,we found the truth as followed.(1)Gases released from water into atmosphere mainly including nitrogen,oxygen,nitrous oxide,methane and carbon dioxide(N2,O2,N2O,CH4,and CO2).Nutrition and light condition were vertically different in the serious eutrophication water body.So that the characteristics of gases releasing from the water were significantly different in each layer of the water body.In the urban serious eutrophication sewage pond,dissolved oxygen concentration was supersaturated.Surface nitrogen,nitrous oxide gases fluxes were significantly higher than those in the lower layer due to the stronger aerobic denitrification in surface water.There were a large number of micro-organisms in sediments and nutrients were liberated from the mud into water continuously.In the slurry interface highly effective denitrification made the nitrogen,nitrous oxide emission fluxes higher than that in the middle.Sediment release methane in the form of bubbles to the top and with the movement of dissolved oxygen rised in water,methane is oxidized to produce carbon dioxide.The underlying methane and carbon dioxide concentrations decreased from bottom to top.During the monitoring test,when the gases fluxes reach the peak from eutrophic water,nitrogen,nitrous oxide,oxygen gases fluxes vertically respective decline rates were 75.0%,88.8%,92.1%;Fluxes of methane and carbon dioxide from the bottom to the surface respective decline rates were 86.4%,92.8%.(2)In this paper,we monitored the gases(N2,N2O and O2)emission fluxes during the treatment by microorganisms and microbial-plant joint in the urban sewage water by the use of in-situ collection means in natural water bodies.And it turned out that,compared with the polluted water without fix treatment(control,trail),microbial agents(Rhodobacters,Phaeroides)and microbes-plant(Eichornia crassipes)united purification were able to significantly reduce the water content of TN.On the other hand,during the fix treatments gases emission were limited.During the microbial agents and microorganisms-plant joint purification treatments nitrous oxide mean release rate were 10.681±1.93 and 5.91±1.72?mol·m-2·h-1,compared with the control,a decline of 16.37%and 53.86%.Nitrogen mean release rates were 1.49±0.33 and 0.87±0.27 mmol·m2·h-1,compared with the control,a decline of 5.7%and 67.5%.Oxygen mean release rates were 1.14 ± 0.25 and 0.29 ± 0.26 mmol·m-2·h-1,compared with the control,a decline of 14.9%and 72.1%.Both of microbial agents and microorganisms-plant joint purification can purify polluted water and reduced the rates of released gases from eutrophic water body.Reduce of gases released may be due to increased microbial and/or water and aquatic plants on the assimilation of nutrients,resulting in nutrient competition,the growth of nitrification and denitrification bacteria and phytoplankton inhibited,thus limiting N2O,N2 and O2 gases produced and released.(3)By monitor the fluxes of gases from Taihu Lake and urban serious eutrophication sewage pond(2#)in JAAS,we just found that the more severe eutrophic degree of the water body was,the higher fluxes of gases released from the water.The total release rates of nitrogen,nitrous oxide,oxygen,carbon dioxide,methane in Taihu Lake were about 8.26±2.28mg·m-2·h-1,15.31±7.88?g·m-2·h-1,1.73±0.75 mg·m-2·h-1,433.0±338.5?g·m-2·h-1,2.1 ± 1.9 mg·m-2·h-1.Gases stratification were not significantly different in Taihu Lake,the mean gases fluxes in ever layers were 0.98?4.18 mg·m-2·h-1,1.3?6.1 ?g·m-2·h-1,0.30?0.75 mg·m-2·h-1,26.7?385.3 ?g·m-2·h-1,0.02?1.3mg·m-2·h-1.But in the serious eutrophication water body,the gases released fluxes were higher than those in Taihu Lake water body.In the sewage pond tested,the total release rates of nitrogen,nitrous oxide,oxygen,carbon dioxide,methane were about 189.2±43.2 mg·m-2·h-1,1368.7±902.9?g·m-2·h-1,171.2±77.2mg·m-2·h-1,1707.5±697.6?g·m-2·h-1,20.11±10.88mg·m-2·h-1.The mean relase rates were about 14.2?158.3 mg·m-2·h-1,39.3?1275.7 ?g·m-2·h-1,1.9?164.5 mg·m-2·h-1,296.5?943?g·m-2·h-1,2.56?10.56 mg·m-2·h-1.Gases stratification were significantly different in sewage pond.Fluxes of nitrogen,nitrous oxide,oxygen,carbon dioxide rised to deepen water.Methane was released more in the bottom.In the sewage pond the water area is smaller and the water flows slower.So it is more prone to water stratification at the same temperature environment and under the same light condition.