Abstract: The Contingent Valuation Method(CVM)is a direct interview approach that uses si - mulated(hypothetical)markets to identify values similar to actual markets.CVM is a promising technique that could potentially help public decision-making.CVM has two major question formats,the continuous and discrete contingent valuation(CV).Lots of empirical studies conducted in various contexts show that the approach is well-accepted by the general public.Based on the result of payment card format,one of the continuous CV,in this paper,we take the dichotomous choice(single-ended and double-ended)question format which belongs to the discrete CV as a tool to analyze the economic benefits of restoring ecosystem service in an impaired river basin,Heihe river basin.In our survey we use a well-designed questionnaire with maps,pictures and figures depicting the reason why the ecosystem of Heihe river basin and Zhangye city has been deteriorating,the measures by which ecosystem services could be restoring from their current level,and the benefits the households in the area could get from restoring ecosystem services.Results from400in-person interviews for single-ended and double-ended dichotomous format respectively indicate that90.2%of the households in Heihe river basin would like to pay for restoring the ecosystem services of Zhangye city.The result shows that the maximum average willingness to pay(WTP)is162.82and182.38RMB yuan per household per year for single-ended and double-ended dichotomous formats respectively.The annual aggregate benefits of restoring ecosystem services of Zhangye city are at least7094.36×10 4 and7946.66×10 4 RMB yuan for single-ended and double-ended dichotomous formats respectively,calculated by the number of the households in1999in the Heihe river basin.This result is a conservative estimate for the economic value of restoring the ecosystem services of Zhangye city because of the positive externalities of restoring the ecosystem services on the outside of Heihe river basin.It has been found that double-bounded format has a tighter confidence interval for the esti-mate of mean WTP than single-bounded format,and is more closely approximate to the true WTP of respondents.Therefore,we suggested that the estimation results of double-bounded format as the total economic value of restoring Zhangye city ecosystem services.The aggregate benefit(pre-sent value)of restoring Zhangye city ecosystem to residents of the Heihe basin is3.7478×10 8 RMB Yuan in the next5years.

Key words: ecological economics, valuation of ecosystem services restoration, contingent val-uation method(CVM), willingness to pay(WTP), Zhangye city, Heihe river basin