Temperature effects on sorption of dissolved organic matter on ferrihydrite under dynamic flow and batch conditions

Abstract Accurately predicting the effect of temperature on soil C storage remains a crucial objective in the effort to understand, mitigate, and adapt to climate change. Associations between soil organic C and short‐range order minerals like the iron hydroxide ferrihydrite contribute substantially to C sequestration, but little is known about how these associations respond to changes in temperature. We investigated the effects of temperature (7, 25, and 45 °C) and dissolved organic matter (DOM) source and fraction on DOM sorption to ferrihydrite‐coated sand in continuous flow and batch systems at circumneutral pH. Our findings demonstrate a positive relationship between temperature and adsorption, especially between 25 and 45 °C. For aquatic DOM, desorption also increased appreciably with temperature, whereas desorption of peat and soil DOM was less sensitive. More aquatic DOM adsorbed compared with soil DOM at all temperatures, but flow studies revealed that aquatic DOM also desorbed at higher rates. Modeling of DOM breakthrough curves using the advection‐diffusion equation with a modified Freundlich isotherm suggested the partition coefficient increased over time. Specific ultraviolet absorbance values of initial column effluents were low, suggesting that aromatic‐rich compounds preferentially adsorbed to the mineral surface. Our results indicate that some circumstances may favor the accumulation of DOM on iron mineral surfaces as temperature increases, potentially removing organic substrates from the accessible dissolved C pool. However, the stability of new associations likely depends on the chemical characteristics of DOM and the conditions under which it adsorbed.