The Chemical Composition In Different Categories Of Soil Water

Soil water is one of the important components in the soil,and acts as a carrier for migration of substances in the soil.Soil water is a link which contacts with the surface water,meteoric water,groundwater and vegetation,and plays a significant role in the conversion of material cycle and water cycle.Studies show that different fractions of soil water have various contributions to plant growth and groundwater.Thus,researches of chemical compositions of different fractions of soil water can provide an important guidance to plant growth and groundwater pollution.This article has selected three typical types of soils in Baguazhou,Nanjing,Jiangsu and one soil from weak permeable layer in Zhongshan,Guangdong,as soil samples to conduct this research.Stepwise centrifugation is used to extract gravitational water,capillary water and effective bound water from four types of soils respectively,studying the moisture content and distribution of chemical composition in different fractions of soil water,exploring the factors affecting the chemistry of different fractions of soil waters.The main results are as follows:1.The content of different fractions of soil water extracted from four types of soils show the same change pattern:capillary water>effective bound water>gravitational water.However,the proportion of each fraction account for total water content mainly varies with soil textures.For example,for three soils with the same pedogenic environment extracted from Baguazhou,the proportion of mobile water?gravitational water plus capillary water?that account for total water content decrease with increasing clay content,indicating that clay content play an important role in content of different fractions of soil water.The proportion of gravitational water account for total water content in Zhongshan soil is higher than those in Baguazhou soil,mainly because Zhongshan soil is sampled below groundwater level.2.The distributions of Zn,Cu,Ni and Cr in gravitational water,capillary water and effective bound water extracted from different sampling soils follow the same pattern that the lowest concentrations of four metals in soil water occurred in capillary water.The heterogeneous distributions of heavy metals in different fractions of soil water may be related with the different residence time and chemical process of different fractions of soil water in soils.The capillary water is usually stored in capillary pores by capillary force,which is difficult to keep heavy metal element with large mass.The gravitational water is the highest mobile and it is vulnerable to rainfall eluviation,which carries metals with high mobility in surface soil down to gravitational water.Effective bound water that strongly absorbed to soil grain surface is mainly affected by mineral weather:ing and/or adsorption-desorption of soil matrix.The benchmarks content of heavy metals in different fractions of soil water are controlled not only by heavy metal content in soil,but also by pedogenic environment.The benchmarks content of heavy metals in different fractions of soil water extracted from Baguahzou different soils are controlled by the heavy metal content in soil.However,the benchmarks content of heavy metals in different fractions of soil water extracted from Zhongshan soil are greatly influenced by ancient seawater.The concentration of Zn,As,V and Cu in soil water from Zhongshan soil which are encountered seawater intrusion are one order of magnitude higher than those in soil water extracted from Baguahzhou.For Baguazhou soils with the same pedogenic environment and mineral composition,the differentiations of metal concentrations between gravitational water and capillary water are increased with increasing clay content of indicating that clay content control the metal exchange between gravitational water and capillary water.The lower the content of clay,the easier for the heavy metals exchange between gravitational water and capillary water.The heavy metal extrange between effective bound water and capillary water are controlled by clay content and organic content.3.The main cations characteristics in different fractions of soil water extracted from different sampling sites are different.For Baguazhou soils,no significant differences of main cations are found in gravitational water,capillary water and effective bound water.However,for Zhongshan soil,effective bound water and capillary water show the similar concentrations of K,Ca,Na and Mg,which are higher than those in gravitational water.The main cations in different fractions of soil water extracted from Zhongshan soils are influenced by the ancient seawater,so Na+ is the main cation.The main cations in different fractions of soil water extracted from Baguahzou soils are mainly from the dissolution of calcium carbonate and other minerals,so Ca²⁺ is the main cation.The concentrations of K,Ca Na and Mg in Zhongshan soil water are significantly higher than those in soil water extracted from Baguazhou soils.The three soils extracted from Baguazhou have the similar mineral compositions and pedogenic environment,soil clay content are the main factors affecting the main cations in different fractions of soil water.The highest content of Ca,Mg and Na are found in soil water extracted from sandy loam.