Temporal And Spatial Differentiation Characteristics Of Soil Water,Salinity And Fertilizer In The Chenier Of Yellow River Delta

With the global climate changing,soil hydrology and soil fertility have been affected by the rise of sea level,the seawater intrusion and coastal erosion to a large extent and the distribution of vegetation is restricted by the spatial pattern of soil water,salinity and fertilizer in the coastal ecosystem.The chenier of Yellow River Delta is one of the three ancient shell ridges in the world,which is the most completely conserved and the only old and new coexistence.It is imperative to carry out the study on the spatial and temporal characteristics and influence factors of water,salinity and nutrients in the chenier of Yellow River Delta.According to the changes of soil,hydrology and nutrients caused by human or natural factors in wetland ecosystem of the chenier,the soils of 4 different habitats in the coastal zone were taken as the research object.The spatial distribution characteristics of the soil water content,hydrogen and oxygen isotopes,soil salt content and nutrients in different habitats were analyzed by the combination of stable isotope technique,field location observation and indoor test analysis.The spatial distribution characteristics of water,salinity and nutrients in different habitats were discussed,which would play an important role in scientific significance for revealing the mechanism of plant community and function in the seashore coastal zone and provide important theoretical guiding significance for the protection and restoration of the degraded coastal zone vegetation.The main results as follows.1.Soil water content increased with the increase of soil depth,which was affected by rainfall,seawater,soil texture,vegetation coverage and soil particle size and other factors.Compared to the beach,?D and?¹⁸O values of surface soil water in the seaside and dune crest were more sensitive to the response of rainwater.It showed that the trend of?D and?¹⁸O values were lower in surface soil and?D and?¹⁸O values were higher under surface soil,which indicated that the soil water in the seawardside and the dune crest would only be supplied by rainwater to a large extent,but the soil water under 60 cm was also subjected to lateral movement of seawater and groundwater recharge.The stagnant water after the rain supplied the surface soil water in the landside,which makes the hydrogen and oxygen isotopes move between the stagnant water and the soil water.2.The pH of the chenier in the Yellow River Delta was within the range of 7.32 to 8.50,which was alkaline.Soil salinity was within the range of 0.76 to 13.57 g/kg.In the horizontal direction from the seaward side to the landside,the soil salinity showed a tendency to decrease firstly and then increased.From the point of view of soil texture,the soil salinity of coastal saline soil was higher than that of shell sandy soil.Soil salinity had obvious seasonality,which had a downward trend in the rainy season.When there was no interference in the rainy season,soil salinity had a tendency to move upwards with the capillary phenomenon because of the concentration of the surface,this effect was most obvious in the coastal tidal zone.The broken shells in shell sand habitat could destroy the capillary phenomenon,thus preventing the salt from moving to the surface.In soil anions and cations,the content of Ca²⁺and Cl^-were higher.The relationship among soil salinity and Na⁺,Mg²⁺,Cl^-,SO₄^2-showed an extremely significant positive correlation and the relationship between soil salinity and K⁺showed a significant positive correlation,but the correlation with Ca²⁺was not significant,indicating that the salt content in different habitats of chenier was mainly sodium salt,magnesium salt,potassium salt,chloride salt and sulfate.Soil salinity and pH showed a significant negative correlation in the study area.3.The contents of soil total nitrogen,total phosphorus and total potassium in the chenier of Yellow River delta ranged from 0.08 to 1.08 g/kg,0.16 to 0.49 g/kg,and 1.50 to 13.41 g/kg,respectively.Compared to beach?bare land?,the soil total nitrogen,total phosphorus and total potassium of seaward side,dune crest and landside had certain vertical distribution characteristics.There was a downward movement trend that the surface layer?0-20 cm?was higher than the surface sublayer?20-60 cm?.The content of soil total nitrogen,total phosphorus showed a seasonal change that the content began to decrease at the beginning of the growth season,then the content was the lowest during the growth season and the content began to rise again at the end of the growth season.4.The microbial biomass C,N and P in different habitats were ranked by the dune crest>the landside>the beach>the seaward side.The microbial biomass C,N and P displayed an obvious vertical distribution in decreasing order of 0-5 cm>5-10 cm>10-20cm>20-40 cm>40-60 cm.Soil microbial biomass C,N and P accounted for 1.09%³.48%,2.62%⁷.27%,0.78%².86%of soil organic carbon?SOC?,total nitrogen?TN?and total phosphorus?TP?,respectively.There were no significant differences between MBC/SOC in the dune crest,the landside and the beach,but significantly higher than that in the seaward side.The changing trend of soil MBN/TN and MBP/TP were the dune crest and the landside>the seaward side and the beach.The abiotic limiting factors of soil microbial biomass C,N and P were soil water content,PH value,salt content and particle sizes in the dune crest and landside.The abiotic limiting factors of soil microbial biomass C,N and P were water content and pH value in seaward side and the beach.The positive correlation among soil microbial biomass C,N and P and soil nutrient were significant or extremely significant in the dune crest,the landside and the beach.The coordination and stability were higher,indicating that the soil microbial biomass C,N and P can be used as biological indices in the evaluation of soil fertility in the chenier of Yellow River Delta.