Simple partitioning of anions and dissolved organic carbon in a forest soil

We analyzed the adsorption characteristics of B horizon soil of a Spodosol (Fragiorthod) as part of a series of studies to evaluate the importance of adsorption processes to nutrient cycling at the Hubbard Brook Experimental Forest, New Hampshire. The results of equilibration experiments using naturally occurring concentrations of sulfate, nitrate, floride, orthophosphate, chloride, and dissolved organic carbon (DOC) were best described using a simple partitioning model rather than either the Langmuir or Freundlich equations. The amount of anion or DOC removed from or released to the solution by the soil was a linear function of the initial amount added to the soil-water system. This relationship, which we term the initial mass (IM) isotherm, was applicable to all solutes evaluated. We interpreted these results as a simple partitioning in which two sources contribute anion or DOC to the system: The soil and solution. The substance of interest is partitioned between soil and solution phases according to a partition coefficient. We calculated soil water distribution coefficients and estimated the reactive soil pools for each anion and DOC, using parameters of the IM isotherm. The IM approach can facilitate a direct comparison of solute-soil interactions for different solutes and soil types.