Characterization Of Soil Salinization In Typical Estuarine Area Of The Jiaozhou Bay And Study Of Soil Salt Leaching In Aquaculture Ponds

In this paper,the typical estuarine area of Jiaozhou Bay was taken as the study area,where soil salinization characteristics and the effects of land use/vegetation cover on the salinization were investigated.Soil samples were collected in the parallel coastal zone,vertical coastal zone and longitudinal profile depth to determine the content of soil salt and multiple saline ions.The correlation analysis and principal component analysis were used to address the general characteristics of soil salinization in the study area.According to the salinization,the aquaculture ponds of severe salinization were selected to study the leaching law of salinity.The aim of this study was to provide important reference for soil salinization in estuary area,and to provide basic data for further improvement of coastal saline alkali soil.The main findings were provided as follows:(1)In the horizontal direction,the soil was of moderate salinization,severe salinization and saline soil state.The farther from the sea(within 1.1 km),the lower the soil salinization degree.This was mainly affected by the St of sea water.2.0 km outside the estuary(including 2.0 km),the St increased firstly and then decreased,and the degree of salinization increased,which was mainly affected by human activities.In the direction of longitudinal profile depth,the soil was of severe salinization and saline soil state;and the St was accumulated in the surface and bottom which was related to the climate,the ocean and the raising of groundwater level.The Na+ and Cl-was the dominant cation and nion,respectively.The distribution of Na+ and Cl-was consistent with that of St.All the salinization indexes,except soil p H,showed moderate and strong variability.(2)The invasion of Spartina alterniflora resulted in the increase of St and salinization,which was mainly determined by the physiological characteristics and growth years in the influenced degree.The degree of soil salinization increased in the aquaculture ponds,which was mainly caused by the use of chemicals in aquaculture ponds.(3)The results of PCA showed that there was a very significant positive correlation between St and K+,Ca2+,Na+,Mg2+,Cl-,SO42-,HCO3-;and the correlation between St and Na+,Cl-was especially significant.There were very significant negative correlations between soil p H and St as well as p H and most of soil soluble ions.The correlation between anion and cation was different,mainly in form of chloride and sulfate.PCA showed that Na+,Cl-,Ca2+,Mg2+ and SO42-could be used as main diagnostic factors of salinization in typical estuarine area of the Jiaozhou Bay.The effect of Na Cl and sulfate on St further affected the degree of salinization in typical estuarine area of the Jiaozhou Bay.(4)The salt content of soil and its leaching solution decreased exponentially with theincrease of leaching water volume.Taking into account the leaching effect and water conservation,the ratio of water and soil near 1:1 could achieve better effect of improvement.In the process of desalting,the contents of Ca2+,Mg2+,K+,Na+ and Cl-in soil decreased,which was mainly determined by the interaction intensity of ions and soil colloids.The content of SO42-first increased and then decreased,which was related to the dissolution of Cu SO4 crystals and the dissolution equilibrium of Ca SO4 precipitates;and the content of CO32-and HCO3-showed an upward trend,which was related to soil ion adsorption and exchange equilibrium,Ca CO3 precipitation and dissolution equilibrium and CO2 dissolution.The rank of desalination ratio of different soil salt ions provided as follows: Cl->Na+>K+>Ca2+>Mg2+>SO42->HCO3-.This was related to the initial content as well as the release of minerals in the soil during leaching and the precipitation dissolution balance occurring.With the increase of leaching water volume,the composition of ions in soil was dominated by Cl-and Na+,which first changed to Na+,K+and SO42-,and finally to Na+,HCO3-and K+.The ionic composition of the soil develops in a benign direction.(5)With the increase of leaching water,the p H value of soil and leaching solution increased,and the increase of p H value was mainly caused by the rise of total alkalinity and little relationship with SAR.Soil desalination process was accompanied by soil alkalization,which requires a further study on the alkalization of salinized soil during desalination.For the phenomenon of alkalization of leaching solution,the measure of irrigation and drainage combined should been taken.