Mechanism And Pattern Analysis Of Wetland Hydrological Connectivity

For wetland ecosystems,the hydrological connectivity and the water flow are important links for the transfer of energy,material,and information between wetland surface water bodies.Hydrological connectivity is a key factor in maintaining the health of wetland ecosystems.Most of the existing studies focus on the impact of wetland hydrological structural connectivity and connectivity intensity on habitat changes from a single process or a single scale.However,few researches have been reported on studying the characteristics and mechanisms of wetland hydrological connectivity,as well as the effect of changes in climate and anthropogenic activities on wetland hydrological connectivity.For this reason,a systematic study of the characteristics of wetland hydrological connectivity and its changes driven by natural and anthropogenic effects has important theoretical and practical significance for restoring wetland hydrological connectivity and ecological functions.In this thesis,Momoge National Nature Reserve was taken as the research object,guiding by the system theory and combining multi-disciplinary theories and methods of physical geography,hydrology,hydrogeology,and computer,the characteristics and mechanisms of wetland hydrological connectivity were studied in terms of water level,water quantity,water quality,isotope and ecological response by great data remote sensing cloud computing,field survey monitoring,numerical simulation and other means,and based on which,wetland hydrological connectivity patterns and comprehensive evaluation system was established.The following main results have been achieved:?1?Distribution and spatiotemporal changes of wetland landscape pattern and hydrological connectivityAccording to great data remote sensing cloud computing,the wetland area of Momoge Reserve currently accounts for 35.4%of the total area of the reserve,mainly distributed along the Nen River in the east,and its connectivity is better than that of the Midwest.From 1984 to 2018,the area of cultivated land in the region increased by2.4 times,while the area of wetlands decreased by 22.84%.The fragmentation of the landscape pattern has increased,and it has changed from a concentrated continuous distribution to scattered scattered.The seasonal surface water in the area accounts for41.6%of the total surface water;the wetland hydrological structure connectivity index decreased from 5.6 to 3.8.The above characteristics reveal that the hydrological connectivity is deteriorating and the wetland is degrading.?2?Hydrodynamic interaction within wetlandsBased on the calculation of water balance,the results show that during the high water period,the water resources in the study area are in a positive equilibrium with an equilibrium difference of 2764142 m³/d.The increase in water resources is mainly due to the flooding of the Nen River flooding area,causing the surface water level of wetland in the flooding area to rise significantly;While in the flat and dry periods,the water resources in the study area are in a negative equilibrium.The decrease of water resources is mainly due to the strong water surface evaporation,and the wetland surface water and groundwater levels are significantly lower than in the high water period.The analysis of the hydrological situation shows that during the rise of the wetland water level,the surface water of the wetland are connected through three patterns of fill and pill,fill and merge and flood connection,which leads to changes in the structure of the wetland hydrological connection and in turn affects the ecological environment of the wetland.Under the control of the terrain,the surface water of the wetland interacts with the shallow groundwater to a certain extent in the lateral or vertical direction,and different depression wetlands is connected under ground by the groundwater runoff.?3?Water chemistry and isotopic connectivityThe study area suffers a semi-arid climate,and evaporation is extremely strong.There is a seasonal hydraulic connection between wetland surface water,groundwater,and Nen River.Shallow groundwater has continuous lateral recharge to wetland surface water,so the hydrochemical types of groundwater and wetland surface water are all mainly HCO₃-Na and HCO₃-Ca·Mg.The strong evaporation causes the degree of mineralization of wetland surface water to reach 2000mg/L,which is significantly higher than groundwater.The hedrochemical type of river water located in the middle and lower reaches of the Nen River is HCO₃-Ca·Mg with low degree of mineralization?<100mg/L?.The water quality characteristics in different seasons indicate that the main source of surface water within wetland recharge in wet season is Nen River water,while in the dry season,the main source of surface water recharge is shallw groundwater.Based on the calculation of the isotope mass balance,the proportion of groundwater recharge to wetland surface water is calculated,which shows that the water in Baihe Lake is mainly derived from farmland reclamation,and the proportion of groundwater recharge is generally less than 5%;The water of Nen River is mainly recharged by precipitation and the proportion of groundwater recharge is also less than 5%;lakes in the western part are mainly connected on the surface during the wet season,when the amount of groundwater recharge is small,accounting for less than 10%.?4?Ecological response of organisms to hydrological connectivityHydrological connectivity affects changes in important environmental factors of wetlands,affects settlement,migration,and reproduction of living things,and further affects the biological connectivity of wetlands.Taking the active area of the indicator species as the control condition,the minimum range of the biodiversity field is determined.In recent years,white cranes have mostly been distributed in areas with densely distributed blisters in the west and north of the reserve.The hydrological connectivity of the active area of white cranes is good.The calculation results of the plant community similarity showed that the biological similarity index of the Erlongtao Wetland and Harnao Wetland was 1,which further explained that the functional connectivity effect in the area was obvious.The temporary connectivity of surface water and permanent connectivity of groundwater made its hydrological and chemicals conditions.?5?Hydrological connectivity patternBased on the wetland hydrological connectivity mechanism,the similarity theory-oriented combination of wetland landscape pattern distribution is used to divide the wetland hydrological connectivity pattern into three types,namely the hydrological connectivity pattern of the wetland in the floodplain,the hydrological connectivity pattern of the wetland in the irrigation area,and the hydrological connectivity pattern of the isolated wetland.The driving-state-response?DSR?theoretical framework establishes a set of comprehensive hydrological connectivity quantitative indicator systems spanning multiple time-space domains.After a quantitative estimation of the hydrological connectivity structure-function degree of the entire Momoge in 2019,the hydrological connectivity of the flooded wetlands in the east and isolated wetlands in the west is relatively good,and that of the irrigation pattern in the central part is poor.The research results provide a scientific basis for the healthy development and management of wetlands.