Comparison and application of calculation methods for ecological water demand of lakes

Since the 1960s,the problem of ecological water demand has gradually attracted attention at home and abroad.The determination of the ecological water demand of lakes is of great significance to lake health and ecological civilization because of an important part of water ecosystem.Since the 21st century,many experts and scholars have also carried out relevant research on the ecological water demand of lakes.Most of the current studies focused on the comprehensive consideration of different hydrological conditions and ecological information,but there are still some problems,such as unclear classification of calculation methods.Therefore,it is necessary to study these methods. Statistical analysis and generalization were used to summarize the concepts,classification,and composition related to the ecological water demand of lakes,and the key words of relevant domestic and foreign literature from 2001 to 2020 were visualized and analyzed by CiteSpace software.The methods of calculating ecological water demand of lakes based on both hydrological principle and ecological principle are summarized,and the applicability of different methods is compared.Finally,taking Taihu Lake as an example,three methods were selected to analyze the minimum ecological water demand,including the minimum water level method,the water exchange cycle method,and the ecological evolution analysis method. It was summarized that lake ecological water demand is "the amount of water of lake ecosystem when it reaches a certain level in a specific area,time and condition".General lakes are mostly the lakes with water input and water output,whose ecological water demand mainly consists of ecological water demand in the lake and inlet and outlet ecological water demand.The keyword cooccurrence network diagrams were obtained,and the analysis shows that current studies of lake ecological water demand at home and abroad mainly focused on two aspects of hydrological principles and ecological principles.The calculation methods based on hydrological principles include minimum water level method,water quantity balance method,and water exchange cycle method,and the calculation methods based on ecological principles include curve correlation method,ecological evolution analysis method and functional method.The annual ecological water demand of Taihu Lake is 3.601 billion m3,2.714 billion m3 and 3.881 billion m3 calculated by the lowest water level method,the water exchange cycle method and the ecological evolution analysis method,respectively.The results of the three methods have some deviations due to different calculation principles and focus.The water exchange period method are greatly affected by the water exchange period of the lake.The lowest water level method are limited by the lack of consistency and representativeness of the water level data of Taihu Lake.The ecological evolution analysis method considers both the hydrological and biological conditions,and its results are the most reasonable. Different methods for lake ecological water demand have a different scope of application.The lowest water level method is suitable for lakes with long series of water level data.The water quantity balance method is mostly used in natural lakes with less human interference.The water change cycle method is not suitable for dry areas or small water storage conditions.The curve correlation method and the functional method both require enough ecological and hydrological data,and the functional method has a wider application.The ecological evolution analysis method focuses on the requirements of biological living space,which is suitable for some lakes lacking ecological data.Taking Taihu Lake as an example,through different calculation methods and comparison with other research results,it is believed that the result of the ecological evolution analysis method is the most reasonable,and the annual ecological water demand of Taihu Lake is finally determined to be 3.881 billion m3.This study provides support for the reasonable calculation of lake ecological water demand and the study of ecological protection,restoration,and high-quality development.

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