Study Of Water Use Efficiency Of Wetland Based On Carbon Flux And Water Vapor Flux Observation

Water use efficiency,which couples carbon and water of wetland ecosystem,connectes photosynthesis,respiration and water consumption together,it reflects the characteristics of CO2 and H2 O circulation and their interaction relationship.At present,compared with the forest,farmland,grassland ecosystem,study of carbon cycle,water cycle and water use efficiency of wetland scosystem are relatively less,which restricts the carbon and water management of wetland,therefore,it is necessary to carry out research of wetland water use efficiency.In this context,based on the eddy coviariance observation experiment lanched in Jinhewan Wetland Ecosystem,Ha Erbin city,Hei longjiang province,analyzed the dynamic viaration mechanism of net carbon exchange both in interdiural and seasonal scale,clarified the conversion law of carbon source and carbon sink and its intensity.Meanwhile,analyzed the viaration charicteristic of water vapor flux in different scales,explored the change regularity of wetland evapotranspiration.Last,water use efficiency of wetland ecosystem was estimated.The main contents and results can be summarized as follows:(1)Based on the experimental data of eddy covariance observation system,characteristics of the carbon flux were analyzed both in diurnal and seasonal scale.The results showed that the net carbon exchange displayed a "U" type distribution in interdiural scale,and reached the peak value at noon.While in seasonal scale,the wetland ecosystem performed carbon source from middle of September to early April of the following year,the rest showed carbon sink,and lasted for about 5 months,the total carbon sequestration was 631.62 g/m2.For whole year,the gross ecosystem productivity was 1571.64 g/m2,cumulative carbon absoption was 203.28 g/m2.(2)Characteristics of water vapor flux variation were analyzed in interdiural and seasonal scale,S-W model was used to decompose the evapotranspiration into evaporation and transipiration,and explored the difference between actual evapotranspiration and potential evapotranspiration and its reason.The results showed that water vapor flux was unimodal in interdiural scale,and achieved its peak at 12:00 ~ 15:00.While in seasonal scale,water vapor flux was high in summer and low in winter,and cumulative value in growing season was 1.83 times higher than non growing season.The annual potential evapotranspiration of wetland ecosystem was 847.17 mm,the actual evapotranspiration was 420.46 mm,the soil evaporation was 182.90 mm,and the vegetation transpiration was 237.56 mm.(3)Characteristics of water use efficiency in the test area were analyzed,and the effects of meteorological factors on water vapor flux were discussed.The results showed that the water use efficiency of Jinhewan wetland was biggest in winter,followed by autumn,spring and summer in turn.In summer and winter,WUE in the afternoon was significantly higher than that in the morning,while in autumn and spring,WUE at noon falled and increased respectively.In seasonal scale,WUE reached maximum in winter,with the average value of 4.47 mg/g,and the falled to 3.64 mg/g in summer,the annual average value was 4.09mg/g.As to influence factors,the cumulative contribution of VPD,temperature and radiation to WUE was up to 89.39%,which were the main meteorological factors affecting WUE.