Effect Of Dam Construction On Water Cycle In Wujiang River Basin

River damming results in the change of natural attributes of rivers,and affects water cycle in the river catchments.In this study,four cascaded reservoirs in Wujiang River basin were taken as research objects,and water samples were collected in January,April,July,October in 2017,respectively,and the hydrogen and oxygen isotopic compositions(?¹⁷O,?¹⁸O,?D)of water samples were measured and analyzed.In order to clarify the impact of dam interception on the water cycle of Wujiang River basin,the study revealed the space-time variation characteristics of hydrogen and oxygen isotopic compositions in the waters and identified the main environmental factors affecting the isotopic composition.we got the following conclusions:?1?The seasonal mean value of?¹⁷O,?¹⁸O,?D of water in Wujiang River basin ranges-4.63^-4.06‰,-8.83^-7.77‰,and-57.40^-49.93‰,respectively.The hydrogen and oxygen isotope composition of the whole watershed showed a certain seasonal difference,and it had a slow positive trend from the winter to autumn,and there was a certain degree of bias in summer,and then an obvious depletion appeared in autumn suddenly.In terms of spatial variation,the overall trend of hydrogen and oxygen isotopes in surface water was gradually positive,which was due to the impact of evaporation and tributary inflow,and the effect of elevation.The isotopes of the profile water body were generally negatively biased with increasing depth.The overall evaporation of Wujiang River basin was not strong,the H-O isotope composition of the river water did not deviate from the local meteoric water line?LMWL?so much.The evaporation in summer?July?and winter?January?was slightly stronger than that in spring and autumn?April and October?in the study area,and the variation characteristics of mass-independent fractionation degree in the four seasons were consistent with the evaporation intensity nearly.?2?The H-O isotope compositions of Wujiang River basin were positively correlated with water temperature in all four seasons.The effect of winter and autumn temperature on the H-O isotope compositions of water were higher than that in spring and summer.The mean value of?¹⁷O in the surface water of the reservoir showed a continuous negative trend in summer and autumn,which was not only due to the effect of precipitation,but also reflected the seasonal difference of rainfall sources.The elevation is the major factor of the hydrogen and oxygen isotope changes in the waters of Wujiang River basin,while the longitude and latitude are not significant.?3?The evaporation rate of Wujiang River basin was the highest followed by spring,while the evaporation rate in winter and autumn was the lowest.The variation of seasonal evaporation rate of Hongjiadu and Wujiangdu reservoirs were the same as that of the whole basin,while Silin and Yinpan reservoirs had the highest evaporation rate in winter,which might because that the original water circulation path was changed for a period of time after dammed,and had affected the evaporation effect of the area.The stratification of the reservoir is related to the reservoir types and the season.Hongjiadu reservoir which belongs to annual regulation showed the most obvious stratification effect,especially in spring and summer,while the water mixing was well in winter,and the stratification of Wujiangdu and Silin was weaker,while the water-crossing Yinpan reservoir had no stratification phenomenon.Hongjiadu reservoir appeared obvious water homogenization phenomenon,while Wujiangdu reservoir which is regulated seasonally,had relatively weak homogenization degree.For Silin and Yinpan reservoirs,the water homogenization effect cannot be formed due to the short regulation time.