The Greenhouse Gases Exchange Mechanism At The Water-air Interface Of Shallow Lakes,Response To Climate Warming And Eutrophication

Increasing concentrations of carbon dioxide?CO₂?,methane?CH₄?and nitrous oxide?N₂O?in the atmosphere are closely related to global warming.Frequent extreme weather events make greenhouse gas emission scenarios more severely in the future.On a hundred-year scale,climate warming and eutrophication is dual dilemma in the lake ecosystem,and still needs to overcome for the long period.It is expected that climate warming and eutrophication will have a strong response to the lake ecosystem greenhouse gases cycle and influencing factors.This study selected the mesocosm?control system?to set up our experiments with different warming patterns?constant warming 4?and variable warming0?8?to keep the input heat consistent?and phosphorus addition(input KH₂PO₄ 25?g L^-1every two weeks)interactive processing treatments.The aims of this study were 1)exploring the variety of greenhouse gas fluxes at the water-air interface,2)analyzing the impact of different environmental factors on greenhouse gas exchange,and 3)discussing the source and sink of greenhouse gases and their transformation.The main results are as follows:?1?The results of the CO₂ exchange mechanism at the water-air interface of the mesocosm showed that the CO₂ flux between different treatments was mainly negative in winter and spring,which reflected in the absorption of CO₂ from the atmosphere.The CO₂flux basically changed from negative to positive in summer and autumn.The normal temperature treatment?C and P?showed strong emissions,and the heating treatment?T,V,TP and VP?showed fluctuating absorption and emission.The results of the total annual CO₂ exchange indicated that the normal temperature treatment behaved as a source of atmospheric CO₂,and the fixed and fluctuating temperature treatments were both a sink of atmospheric CO₂.Environmental factors,such as conductivity,DO,p H,DOC,TN,TP,NO₃^--N,NH₄⁺-N,Chl.a,submerged plant PVI index,and floating-leaf plant coverage,significantly affected the CO₂ flux in the mesocosm.The heating treatment had a significant inhibitory effect on the CO₂ exchange process in the mesocosm.The effect of phosphorus addition on the CO₂ flux is not significant,but the CO₂ flux of the phosphorus addition treatment is relatively lower under the same temperature rise scenario?C>P;T>TP;V>VP?.Predicting the impact of warming on CO₂ exchange can also be positive.The water column where early warming promotes the lush growth of submerged plants may help to reduce the CO₂ emissions.?2?The results of the CH₄ exchange mechanism at the water-air interface of the mesocosm showed that the CH₄ exchange process presented a strong emission during the whole experimental period,and the CH₄ flux of different seasons was summer>autumn>spring>winter.There as an order of magnitude difference in CH₄ flux between different seasons.The results of the total annual CH₄ exchange showed that all treatments acted as sources of atmospheric CH₄ during the whole experimental period.The CH₄ flux in the mesocosm was significantly affected by conductivity,DO,p H,DOC,TP,NO₃^--N,NH₄⁺-N,Chl.a,submerged plant PVI index and floating-leaf plant coverage.The correlation between CH₄ flux and TN was not significant in the different treatments.The interaction of different heating patterns and the phosphorus addition significantly promoted the CH₄ emission between the water-air interface in the mesocosm,but the direct effect of heating or phosphorus addition was not significant.It is predicted that the interaction between warming and phosphorus addition can significantly enhance the CH₄ emission of the shallow-lake in the future.The warming situation is more severe,and more attention needs to be paid to CH₄ emission reduction measures.?3?The results of the N₂O exchange mechanism at the water-air interface of the mesocosm showed that the N₂O exchange process was active,and all treatments can show the conversion characteristics of emission and absorption during the whole experimental periods.The results of the total annual N₂O exchange showed that the treatment without phosphorus addition behaved as a source of atmospheric N₂O,and the treatment with phosphorus addition behaved as a sink of atmospheric N₂O.The N₂O flux in the mesocosm was significantly affected by DO,DOC,TP,NO₃^--N,NH₄⁺-N,Chl.a and submerged plant PVI index.The correlation between N₂O exchange and conductivity,p H,TN,floating-leaf plant coverage was not significant in different treatments.Warming significantly promoted the N₂O emission at the water-air interface,which was consistent with the metabolism theory.There was no significant difference in the N₂O exchange process between different heating patterns.The phosphorus addition had a significant inhibitory effect on the N₂O emission process at the water-air interface.It is predicted that warming in the future can promote the conversion of lake N₂O as a source,while phosphorus addition can promote the conversion of lake N₂O as a sink,but the contribution to lake warming effect is still very limited.