| Inland fresh waters are recently recognized to be important sources of atmospheric methane(CH4)and nitrous oxide(N2O).In recent decades,large inputs of domestic,livestock and industrial wastewater into inland fresh waters greatly enriched surface water C and N nutrients,directly resulting in higher concentrationsand fluxes of CH4 and N2O in the surface water.Recently,inland fresh waters have received much attention worldwide for yet unclear patterns and fluxes of CH4 and N2O.Here,we conducted a meta-analysis by integrating 948 data observations from 129 published literature to quantify global inland water CH4 and N2O fluxes and emission factors.Five inland water ecosystems were included in this analysis,such asriver,reservoir,lake,pond and stream.We divided our data into four climatic regions by latitude,consisting of tropical,subtropical,temperate and polar zones.We compared the CH4 and N2O fluxes among various inland fresh watersystems ordifferent climatic zonesand therebytorevealthekey factors influencing CH4 and N2O fluxesfrom inland waters.The main results of this study are presented as follows:1.The mean CH4 fluxes from rivers,reservoirs,lakes,ponds and streams were respectively 10.10,3.52,2.92,21.15 and 1.82 mg m-2 h-1.All of these water types,the mean flux of CH4 released from ponds was the highest,and ranged from 3.90 to 38.38 mg m-2 h-1.CH4 flux averages 1.82 mg m-2 h-1 in streams that was the lowest in all water types ans ranged from 1.2 to 2.45 mg m-2 h-1.The mean N2O fluxes from rivers,reservoirs,lakes,ponds and streams were respectively 65.24,60.67,35.59,43.42 and 125.95?g m-2 h-1.All of these water types,the mean flux of N2O released from streams was the highest while that from lakes was the lowest.2.Significant difference were found between the floating stactic chamber technique and diffusion-model method while measuring CH4 and N2O fluxes released from rivers,and the fluxes measured by the diffusion model method was higher than those measured by the chamber technique.The mean flux of CH4 from reservoirs measured by the chamber technique was nearly equal to that measured by the model method,what is more,the mean fluxes measured by the inverted funnel method were lower than those measured by the above two methods.But the mean flux measured by the chamber technique was higher than that measured by the model method in the lake.The mean fluxes of N2O from rivers,reservoirs,and lakes measured by the chamber technique were higher than those measured by the model method.3.The CH4 fluxes from rivers averaged 16.28 mg m-2 h-1 in the subtropical zone and that was the highest flux among various climatic zones,but showed the lowest in the polar zone.The mean CH4 flux from reservoir was significantly higher than those in other climatic zone,The mean fluxes from lakes showed no obvious differernce between the tropical zone and subtropical zone,but in the polar zone,the mean flux was the lowest.The mean flux of N2O from river in the tropical zone was the highest but that was the lowest in the polar zone.The N2O flux from reservoirs was significantly higher in the tropical zone than those in other climatic zone.The mean flux of N2O from lakes was higher in the temperate zone than those in the subtropical zone and polar zone.In the subtropical zone,streams showed the highest mean N2O flux,and the mean flux in the temperate zone was slightly higher than that in the tropical zone.4.By correlation analysis,CH4 flux from inland fresh waters had significant positive correlation with water temperature,and positively related to total organic carbon(TOC),but the flux had a significant negative correlation with water depth and water dissolved oxygen(DO).The N2O fluxes of inland fresh waters positively related to water temperature,nitrate(NO3-),ammonia(NH4+)and DO. |
PDF Full Text Request