| The reproducibility of potentiometric titrations using a copper (II) ion selective electrode increases directly as a function of dissolved organic matter (DOM) concentration, measured as dissolved organic carbon. Conditional stability parameters (Log(K1), Log(K2)), calculated from titration curves using a 2-ligand Langmuir Isotherm, are also dependent on DOM concentration explaining 20% to 60% of the variation reported for these parameters in the literature. The effect of DOM concentration on Cu 2+ complexation is greater for allochthonous DOM, which also exhibits higher charge density and higher affinity for Cu2+, than autochthonous DOM (p < 0.05). The Cu2+ complexing properties of DOM collected from surface freshwaters depend primarily on allochthonous DOM and cumulative hydrologic residence time (p < 0.05) by approximating exposure to transformation and fractionation processes. Comparison to experimental transformation and fractionation processes in micro-reactors suggests that photochemical decomposition, microbial decomposition, and adsorptive fractionation could contribute to the observed pattern of Cu2+ complexation. |
