| The modern Yellow River Delta is located at the junction of land and sea at the end of the Yellow River.It has the most complete warm temperate wetland ecosystem in China and is also a typical groundwater dependent ecosystem.The shallow groundwater is an important part of the ecological water cycle in the Yellow River Delta,and the dynamic change of groundwater plays an important role in soil water and salt migration,vegetation growth and distribution,and biodiversity in the region.In addition,groundwater carries a large amount of soluble nutrients into the sea,which has an important impact on the coastal ecosystem.The analysis of dynamic changes and influencing factors of underground diving in the Yellow River Delta will provide scientific and technological support for the sustainable development of regional groundwater ecosystem.This study focuses on the modern Yellow River Delta as the research area,and is based on hourly groundwater depth and electrical conductivity data from 16 observation points in the study area from June 2019 to May 2021.With the help of data on hydrogeology,meteorology,land use and other factors,mathematical statistics,time series analysis,and spatial analysis were used to analyze the spatio-temporal dynamics and influencing factors of groundwater depth and electrical conductivity.The results are as follows:(1)Temporal and spatial variation of shallow groundwater depth in the modern Yellow River Delta.The shallow groundwater depth in the study area has a relatively small average value of 1.35 meters,with strong seasonal variations and significant spatial differences.The temporal variations in shallow groundwater depth exhibit short-term changes in the form of sine waves,inverted "U" shapes,and double peaks.The daily fluctuations in groundwater depth are frequent,and the daily amplitude of groundwater depth has significant seasonal characteristics.The seasonal changes in groundwater depth show a sharp decline in the summer with rising water levels,a rapid increase in depth in the fall,and relatively small changes and relatively stable conditions in winter and spring.The spatial distribution of shallow groundwater depth shows significant differences,with greater depth in the southern part of the study area,and smaller depths in the central eastern region and near Diao Kou in the north.The spatial variability of shallow groundwater depth in the study area ranges from 0.06 to 0.58,indicating moderate variability.The coefficient of variation for shallow groundwater depth in the front zone of the Yellow River estuary is higher,while the coefficient of variation in the observation wells distributed along the north-south axis in the central region is relatively smaller.(2)Temporal and spatial variation characteristics of shallow groundwater electric conductivity(EC)in the modern Yellow River Delta.The temporal variation of the EC of shallow groundwater in the study area has obvious stability,and the spatial distribution shows good continuity.The temporal variation of shallow groundwater EC was as follows: the monthly variation range of EC was 1.16S/m～1.86S/m,and the temporal variation was stable,and Spearman rank correlation coefficients were all greater than 0.90(P<0.01).The spatial characteristics of the EC of shallow groundwater are as follows: the EC of groundwater in the study area is relatively large,with an average value of 1.44S/m and high salinity.The spatial distribution characteristics are as follows:the shallow groundwater EC value in the northern coastal area is larger;The groundwater EC value near the Yellow River is low.The coefficient of variation of groundwater EC in 16 Wells ranged from 0.07 to 0.62,which belonged to weak and moderate variation.The spatial continuity of groundwater EC was good,and the coefficient of Spearman rank correlation was high.(3)Analysis of influencing factors of shallow groundwater depth and conductivity.Shallow groundwater depth and conductivity are strongly responsive to precipitation.The influence of temperature and evaporation on groundwater depth and conductivity is similar.The influence of temperature and evaporation on groundwater depth within one day is obvious.The change of groundwater conductivity lags behind the change of temperature by 3～4 months,and the change of evaporation by 2～3 months.The Yellow River and the ocean have an important influence on the groundwater depth and electrical conductivity in the region.The groundwater depth of DZ13 observation well and the ocean tide have the same time-frequency information.The results of Geo-detector analysis show that the spatial heterogeneity of groundwater depth is influenced by the synergistic effect of soil texture and other factors.The spatial anisotropy of groundwater conductivity has the greatest synergistic effect with other factors. |
