The free-solution diffusion coefficient of boron: influence of dissolved organic matter

Abstract

The free-solution diffusion coefficient for boron, which is necessary for diffusional flux calculations, was measured in a variety of media, including seawater, by the diaphragm-cell method. Results show that, over a wide range of solution compositions, the free-solution diffusion coefficient for boron, at ionic strengths of 0.5–0.6 M, is constant at 1.12 ± 0.02 × 10 −5 cm 2 s −1. In the presence of dissolved organic matter from pore waters of marine sediments, corresponding to 30 mg l −1 dissolved organic carbon, boron diffusion is significantly slowed relative to other cases. Quantitative results allow calculation of a composite distribution coefficient that should be useful for approximately correcting total dissolved boron concentrations in marine sediments for organic-boron complexes.