The effect of pH on sulfate adsorption by a forest soil

Acidic deposition and forest clear-cutting are disturbances that have resulted in increased, acidification of northeastern forest ecosystems. This study was conducted to evaluate whether acidification processes can significantly affect adsorption processes that are important in regulating sulfate transport and cycling in a Spodosol at the Hubbard Brook Experimental Forest, New Hampshire. The results of adsorption experiments demonstrated that small changes in solution pH have a large effect on sulfate adsorption characteristics of mineral soil at Hubbard Brook. The ability of the soil to remove sulfate from solution increased as the pH of the solution was decreased, with a maximum removal occurring at about pH 4.0. Through the use of initial mass isotherms, we determined that sulfate removal depended upon (1) the ability of the soil to partition sulfate between the soil and solution phases and (2) the amount of reactive native sulfate that is present in the soil. Our analysis demonstrated that both these soil properties depend strongly upon solution pH.