Equilibrium Concentrations of Major Cations and Total Alkalinity in Laboratory Soil-Water Systems

Abstract

Three soils and four waters were used to prepare laboratory soil-water mesocosms. Soil-water mesocosms contained 5-cm-deep layers of soil and 21 L of water from each of the four sources: artificial rainwater, stream water, saline well water, and seawater. Water pH, conductivity, major cations, and total alkalinity were measured at intervals for 200 days. In some instances, equilibrium was not attained during the trial. Soils from the Coastal Plain and Blackland Prairie regions of Alabama caused greater increases in intensities of variables in rain and stream water than did Piedmont Plateau soil, while conductivity, calcium, sodium, and total alkalinity in rain and stream water increased most in mesocosms with Blackland Prairie soil; magnesium increased most in mesocosms with Coastal Plain soil. In mesocosms with saline well water and Blackland Prairie soil, there were changes in all measured variables other than pH and conductivity. In mesocosms with seawater and Blackland Prairie soil, only calcium, magnesium, and potassium in the water were different from the original source water. Shaker experiment revealed that equilibrium concentrations of water quality variables increased as the ratio of soil to water increased.