Molecular Characterization of Dissolved Organic Matter As Influenced By Redox Oscillation Conditions.

In redox dynamic wetlands, the onset of anoxic and oxic condition, affects the biogeochemical processes in soil. Colloid particles- having size ranges between 1 nm to 1 μm with a very large specific surface area and high reactive site densities- are very important for the persistence of soil organic carbon. However, the operational definition of dissolved organic matter (DOM, <0.45 μm), underestimates the contribuion of colloidal phase by including colloidal fractions of diameter <0.45 μm as dissolved fraction. Despite the size dependent reactivity of colloids and OM, few studies have been conducted for molecular level characterization of mineral-organic matter association to assess the retention, transportation of OM under redox oscillation condition. The main objective of this study is to evaluate the molecular characteristics of OC in different size fractions under different redox oscillation conditions. In this experiment, soil samples were incubated for two alternate redox oscillation events followed by separation into 4 different size fractions: 1000-450, 450-100, 100-2.3, and <2.3 nm. Finally, samples were analyzed to determine the colloid and organic carbon concentration, and δ¹³C isotope values through Isotope Ratio Mass Spectroscopy (IRMS). Samples were also examined through X-ray photoelectron spectroscopy (XPS). Our preliminary results suggest that under redox oscillation condition, the molecular characteristics of OM were also varied among different sized fractions. This study will allow us to systematically evaluate the colloid-OM association under redox dynamic environment that is crucial to predict the influence of climate change on the stability of OM.