Water-salt Characters Of Groundwater And Ecological Effects In The Yellow River Delta

There are multiple wetlands in the Yellow River Delta with vulnerable ecologicalenvironment. Owing to special geographical location and natural condition, groundwaterin this area bears important ecological functions and generates obvious ecological effects.Therefore, in order to provide the scientific evidence and guidelines for the ecologicalregulation in the lower Yellow River, the ecological restoration in the Yellow River Deltaand the implement of the Blue Shandong Peninsula Economic Zone and the Yellow RiverDelta High-efficiency Ecological Economic Zone strategy, it is of great significance torealize the water-salt dynamic characters of the groundwater, especially the phreatic waterin this area.Based on the field survey, observation and sampling analysis, four objectives havebeen achieved. First of all, combined with hydrological and meteorological data, thedynamic trends of groundwater level in the Yellow River Delta were analyzed, and thechemical features and formation mechanisms of the phreatic water in different regionswere discussed by the methods such as mathematical statistics, Piper diagram, ions ratioand so on. Secondly, geostatistics was used to analyze spatial variability of the mainsalinization parameters at different soil depths. Combined with the Cl^-content distributionpatterns in columnar soil samples in the vadose zone, the key driving factors for spatialdistribution of soil Cl^-content were analyzed. Thirdly, DCCA method was used tointerpret the relationship between the distribution patterns of vegetation communities andenvironmental factors. Meanwhile, multiple stepwise regression method and correlationanalysis were used to determine the relations between NDVI and major factors. Based onthe above analysis, the key factors influencing plant growth and distribution wererevealed, and the relationship between groundwater and vegetation in the aspects of waterand salt were further elabarated. Finally, RS, GIS and some other advanced technologies were adopted to assess and forecast the health of the coastal wetlands in the Yellow RiverDelta. Following results are obtained:（1） The depth to the groundwater （0.50².50m） in the Yellow River Delta is shallow,and that in the coastal inshore it is generally less than1.00m. The annual groundwaterlevel of local areas of the river highlands on both sides of the Yellow River’s current flowpath and coastal inshore belongs to the basically stable type. In these areas, genetic typeof groundwater regime is the type of "infiltration-runoff" or "hydrology". And the otherparts of the area, the annual groundwater level belongs to the type of fluctuation whichgives priority to the type of "down-up-down". Besides, genetic type of groundwaterregime in these areas is type of "infiltration-evaporate". As a whole, the annual change ofthe groundwater level mainly shows relatively stable seasonal change in the Yellow RiverDelta, as well as the inter-annual groundwater level is in a state of dynamic equilibrium.（2） The Cl^-and TDS concentrations of shallow groundwater possess conspicuousdirectional spatial variability and gradually increase along the groundwater flow direction,proving the strong relativity between then and showing that Cl^-is the most critical ion ofshallow groundwater. In addition, from the recharge area to the discharge area, shallowgroundwater changes from the Na⁺-Mg²⁺-Ca²⁺-Cl^--SO42-facies to the Na⁺-Mg²⁺-Ca²⁺-Cl^-,Mg²⁺-Na⁺-Ca²⁺-Cl^-and Na⁺-Mg²⁺-Cl^-facies, finally evolves into Na⁺-Cl^-facies in thecoast.（3） The changes of the Yellow River water course and seawater intrusion are keydrivers to form the chemical characteristics of shallow groundwater in the region.Underthe function of the two main drivers, the chemical characteristics of shallow groundwaterhas formed with mixing, evaporation concentrating, mineral dissolution, cationexchange/adsorption and human activities. And the effects of those factors are apparentlydistinguishied in different regions.（4） Under shallow water table conditions, it is a common phenomenon that Cl^-inphreatic water migrates and accumulates to vadose zone. Spatial distribution and variationof soil Cl^-content is controlled by Cl^-concentration in phreatic water. Further, Topography through redistribution of water, gas and heat controls the direction of the Cl^-migration in the unsaturated zone soil and enrichment region. As a result the soil Cl^-content is very significant within the changes in topography.（5） Groundwater is a sensitive element of the ecological environment in the YellowRiver Delta. The depth to groundwater and Cl^-concentration in phreatic water are thecritical factors of groundwater. Especially the later causes typical regionaleco-environmental effects by influencing the vegetation. Cl^-concentration in phreaticwater suitable for the growth of Suaeda heteroptera, Tamarix chinensis and Phragmitesaustralis are10.0³5.0,5.0²2.5and0.1¹5.0g·L^-1, respectively.（6） Healthy, sub-healthy and morbid area accounts for18.9%（514.94km²）,69.6%（1892.94km²） and11.5%（311.92km²） respectively in the coastal wetlands health of theYellow River Delta. During the period from2012to2020, habitat quality in estuarinewetlands will be gradually improved to the healthy direction, but the environmentalquality of northern and southern parts of the beach area and the Shenxian’gou flow pathin the local areas will have a certain decline under natural and human impacts together.During the development and construction of the Yellow River Delta, more attentionshould be paid to the interrelationship between grounderwater and vegetation. At thesame time, effective artificial regulation measures should also be adopted, to ensure theecological health of coastal wetland ecosystems.