An Traceable Simulation Of The Water Circulation Process Of Multi-sand River Wetlands Based On Isotopes

Sanmenxia Reservoir is the first large-scale water conservancy facility on the Yellow River,with a control area of more than 90%of the Yellow River Basin.After operation,a large amount of sedimentation occurred,which seriously endangered the flood control safety of the upstream cities.In 1974,Sanmenxia Reservoir Clear muddy"mode.Due to the special operation mode of the Sanmenxia Reservoir,a unique wetland in the sediment-rich river—Sanmenxia Reservoir Wetland.The wetland in the Sanmenxia Reservoir area is an important winter migratory bird habitat in the middle reaches of the Yellow River,and has both important natural and social service functions.Affected by climate change and human activities,wetlands in the Sanmenxia Reservoir area face multiple threats such as area shrinkage,ecosystem degradation,water and metal pollution,and biodiversity loss,which seriously affect the health of wetland ecosystems.In this context,based on field surveys and field sampling analysis,this paper systematically analyzes the changes in the main water cycle elements of the wetlands in the Sanmenxia Reservoir area and the stable hydrogen and oxygen isotope composition characteristics of different water bodies,and establishes that precipitation,river water,groundwater,and soil water are different in the reservoir.Based on the complementary relationship under operating conditions,based on the stable isotope traceability method,a mixed isotope mass model was constructed to simulate the water cycle process of the wetlands in the Sanmenxia Reservoir area under different operating modes of the reservoir.The main content and results of the paper are as follows:?1?The characteristics of the wetland water cycle elements in the Sanmenxia Reservoir over the years are as follows:the average rainfall from 1974 to 2017 was 531.32 mm,showing a significant downward trend,the average evaporation was 1135.58 mm,showing a very significant downward trend;the average inflow was 28.471 billion m³,the average outflow is27.7 billion m³,all showing a very significant downward trend.From 1997 to 2017,the average soil midstream is 10.103 billion m³,showing a significant upward trend,the average underground runoff is 17.216 billion m³,showing a downward trend.Different modes of operation of reservoirs affect the changes of evaporation and runoff of wetlands.?2?The composition characteristics of stable hydrogen and oxygen isotopes in river water,groundwater,and soil water were analyzed.It was found that the stable hydrogen and oxygen isotopes in soil water in wetlands were the most abundant,followed by river water,and the groundwater was the most depleted.The correlations between?¹⁸O and?D in river water,groundwater and soil water are:?D=6.704?¹⁸O-0.418,?D=6.384?¹⁸O-2.411,?D=4.88?¹⁸O-19.838.The changes of stable hydrogen and oxygen isotopes in river water,groundwater and soil water are as follows:river water is higher in April than January in the storage period of the reservoir,and higher in August than July in the reservoir discharge period;groundwater and soil water The isotope content during the reservoir discharge period is higher than the reservoir storage period.The stable hydrogen and oxygen isotopic content of river water during the reservoir storage period showed an overall increase trend,and the reservoir discharge period showed an overall decrease;groundwater decreased during the reservoir storage period,and the discharge period increased slightly;soil water was stored in the reservoir.Both the water period and the drainage period showed a decreasing trend along the way.Analysis of influencing factors found that the changes in the composition of stable hydrogen and oxygen isotopes in different water bodies in the wetlands of the Sanmenxia Reservoir were caused by precipitation evaporation and water withdrawal from human activities.The water supply relationship also behaves differently under different operating modes of the reservoir.During the reservoir storage period,the reservoir water level is higher than the groundwater level,and the wetland river water supplements the groundwater.During the reservoir discharge period,the reservoir water level drops below the groundwater level.Leakage recharges river water.?3?Three models of IsoSource,IsoError and SIAR were used to simulate the water cycle process of the wetlands in the Sanmenxia Reservoir area under different operating modes of the reservoir.Because the calculation results of the SIAR model are less uncertain than the results of the other two models,the SIAR model was selected to simulate and calculate the contribution rate of each water body in the wetlands of the Sanmenxia Reservoir area.The results show that during the reservoir storage period,river water,soil water,and precipitation supplement groundwater.River water contributes the most to groundwater,accounting for about 40?60%;soil water is the second,accounting for 30?40%,and the contribution of precipitation is the smallest.Only 10?20%.During the reservoir discharge period,groundwater,soil water,and precipitation supplement river water.The contribution of groundwater to river water accounts for about 30?70%,and the contribution of soil water to river water accounts for about 10?50%.The contribution of precipitation to river water is small,accounting for only 10?20%.