Adsorption of dissolved organic carbon to mineral soils: A comparison of four isotherm approaches

Abstract

The partitioning of dissolved organic carbon (DOC) within mineral soils is primarily controlled by adsorption to soil particle surfaces. We compare the theoretical limitations and modeling accuracy of four isotherm approaches to describe DOC partitioning to soil surfaces. We use 52 mineral soil samples to create linear initial mass (IM), non-linear, and Langmuir isotherms, all relating the initial solution concentration ( X i) to the amount of DOC adsorbed or released from soil surfaces. The Langmuir isotherm is also used with final concentration ( X f). The IM isotherm failed to meet theoretical assumptions and provided poor fits to experimental data. The non-linear and Langmuir X i approaches had good fits to experimental data, and the Langmuir X i approach had the most robust estimates of desorption capacity. Both Langmuir X i and X f isotherms hold the advantage of estimating the maximum adsorption capacity, yet the X f isotherm is a better reflection of adsorption processes.