The Impact Of Landscape Dams On The Water Cycle In The Shiyang River Basin Based On Stable Isotopes

The sustainable development of water resources in global arid regions is being affected by dams.Although the disruption of water cycles by large dams is evident,smaller dams are more numerous and are built at a faster pace,so their influence on the water cycle system should not be ignored.Small dams come in a variety of types,primarily those built for river landscape purposes in and around cities.At present,landscape dams in arid regions have completely altered the processes and mechanisms of the water cycle.However,due to a lack of reliable census data and records,the impacts of landscape dams on the water cycle in arid areas have not been fully elucidated.This calls for a better understanding of the role of landscape dams in the water cycle in arid regions.Therefore,it is imperative to clarify the actual impact of landscape dams on the water cycle in arid watersheds.This paper focuses on the inland river basin of the arid region in Central Asia,the Shiyang River Basin.Using the stable isotope data of river water,landscape water,groundwater,and precipitation collected from the ecological environment observation network established within the basin,and supplemented by meteorological,hydrological data and remote sensing technologies,the spatiotemporal evolution rules of the hydrogen-oxygen stable isotopes in the water under the intervention of the landscape dam in the Shiyang River Basin are analyzed.The impact mechanisms of the landscape dam on each main link of the water cycle are explained,and the comprehensive impact of the landscape dam on the regional water cycle is clarified.The following conclusions are drawn:（1）Hydrogen and oxygen stable isotope values in river water vary with the dry and wet seasons.Comparing the changes of hydrogen and oxygen stable isotope values in river water in the dry and wet seasons,the hydrogen and oxygen stable isotope values are more enriched in the dry season and more depleted in the wet season.From the changes along the river,the hydrogen-oxygen stable isotope values showed a trend of gradual enrichment from the upstream river water to the midstream landscape water.From the relationship betweenδD andδ¹⁸O of different water bodies,the slope and intercept of the landscape water line are lower than those of the upstream river water line,indicating that the evaporation effect of the landscape water is stronger than that of the upstream river water.And the slope and intercept of the landscape water line are the lowest in summer,indicating that the evaporation effect of landscape water is the strongest in summer.（2）Landscape dams change the main links of the water cycle,such as precipitation,runoff and groundwater,in their areas through evaporation and infiltration.First,local recirculation of water vapor from landscape dams due to evaporation can contribute up to 21.1%to regional precipitation（June 2019）.Second,comparing the evaporative loss ratio f of landscape water to upstream river water reveals that evaporation from water storage at landscape dams causes greater water loss than upstream river water.In addition,both stable isotope data and river hydrologic characteristics indicate that landscape water has a more frequent exchange relationship with its surrounding groundwater,suggesting that landscape water is an important source of recharge for its surrounding groundwater.（3）Under the cumulative influence of multiple landscape dams,the hydrologic processes of the river in its natural state in the area where it is located and its surrounding areas have been significantly altered.The estimation results of the isotope water balance model show that about 21%of the water flowing into the landscape dam area is consumed by evaporation,and its water yield Wy is about-12 mm,indicating that the water expenditure in the landscape dam area is greater than the income,and the water loss is mainly generated through the expenditure term of evaporation.In addition,the variation of ITTPs,a proxy for water transit time,indicates that the water transit time for landscape water in the middle reaches of the Shiyang River is longer than that for upstream river water.Thus,the cumulative effect of multiple landscape dams alters the water cycle process in the entire landscape dam area.