| Wetland is the unique multi-purpose ecosystem and the ecological landscape with biodiversity, and it is also the most important living conditions for human being. Wetlands function as the downstream receiver of water and waste from both natural and human sources, they stabilize water supplies, thus ameliorating both floods and drought, and they also have high productivity to provide multiform resource for human society, therefor, wetlands play an irreplaceable role in maintaining ecological balance and promoting national economic growth. However, affected by a series of factors, such as the rapid increasement of population in China, continuous shortage of industrial and agricultural water use, global climate change, wetlands in China have faced severe situations, as a result, many wetlands disappear at alarming rates, and considerable parts can never be resumed, whereas, wetlands protection and restoration become the foremost problem to be resolved.Water is the prime factor to shape and maintain the wetland ecosystem, the change of water status is very meaningful for wetland function study and critical stage judgement. Of the water circle factors in wetland, the aquatic macrophytes evapotranspiration (ET) is very difficult to measured derectly, and it is also a key point for the study of water dynamic variety in wetland. By experimental test and model estimation, Mulit-temporal scale ET of the main underlying type in wetland, reed swamp and open water, is evaluated, the effect of aquatic macrophytes ET on open water and the change laws of ET are investigated, the climatologic characteristics that affect wetland ET is analysed, and the possible change trend of ET loss in future period is predicted. The study in this paper can provide comprehensive support for wetland hydrology management and wetland protection. Zhalong wetland is chosen for studing in this paper, the main contents and achievements are as followed:(1):Derect measurement for ET of aquatic macrophytes in wetland, simulation of ET process by mathematical modelSystemic summarization is made for ET evaluating methods on different underlying types, considerable contrasts are made for different mathods, as a result, "compensatory lysimeter with three cylinders" is developed according to the characteristics of Zhalong wetland, and it is proved that this lysimeter is befitting for measuring ET loss of the saturated reed swamp, the patent applications of the measuring method and device are authorized by the State Intellectual Property Office of PRC. Contrastive experimental test is carried out in Zhalong wetland from 2004 to 2005 (during reed growing season from May 16 to Oct.16), and the function of reed ET to open water is analysed, by use of the actually observed data, a simulation equation of the ET in Zhalong reed belt is established with a high correlative coefficient, which is concerned to the factors of air temperature, wind speed, relative humidity, and reed height and leaf area.(2):The establishement of empirical model for evaluating reference crop ET in Zhalong wetland regionBy analyzing the relationships between FAO56 reference evapotranspiration (RET) and each meteorological variable (the data set is from eight meteorological stations around Zhalong wetland), a statistical model for estimating RET is established. The correlation coefficients (R2) and root-mean-square error (RMSR) are chosen for evaluating the fitting efficiency to RET. After selecting from the meteorological variables that influence ET processes, the essential variables are chosen and some collinearity variables are removed. Through permuting and combining, the essential variables and other candidate variables, different combinations are introduced in various fitting expressions, finally, the model couped with monthly maximum temperature (Tmax), minimum temperature (Tmin), precipitation (P) and wind speed at 2 meter height (U2) is established. Application shows that it can serve as a valuable tool for wetland ET evaluation.(3):The analysis of climatic reasons that affect wetland ET changeData set of five meteorological stations around Zhalong wetland viz. Qiqihar, Fuyu, Lindian, Dumeng and Tailai is used for wetland ET estimating in the period from 1961 to 2000, the annual ET on reed swamp shows degressive tendency, the decrease in recent 40 years is 92mm. The change trend of meteorological factors in wetland area is detected, the results show that significant increasing trend is found of Tmin in recent 40 years in the wetland, however, no significant increasing trend is found of Tmax, and their change shows asymmetry, the U2 shows significant degressive trend, and no evident change of P in study site is detected, the sensitivity analysis shows that Tmax and Tmin are two dominating factors that influence ET markedly, and the difference of rising rate between Tmax and Tmin determines the change trend of ET, the rising of average temperature does not means the increasing trend of ET, in the periods that the rising rate of Tmin exceeds that of Tmax obviously, Tmin counteracts the positive influence of Tmax to ET, the ET can show a decreasing trend as a result. The differential eguation described the change rate of ET, Tmax and Tmin is provided in this study.(4):The possible ET loss prediction of wetland in future period, the calculation of additional water consumption by ET based on climate change.With the empirical model and two climatic scenarios, in future period from 2001 to 2060, viz. linear extrapolation of climatic trends and the predictions of four GCMs (Hadcm3, CCSRNIES, CSIRO-Mk2 and CGCM1) are assumed to calculate the possible ET loss in Zhalong wetland. |
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