Soil Colloid Release and Stability Affected By Dom Under Different Redox Conditions.

Soil colloids, often defined as entities with sizes < 1.0 μm, have attracted much attention because they have small size and large surface area leading to their high reactivity with and ability to facilitate the transport of contaminants in the subsurface environment. Soil organic matter (SOM) coatings on colloids often dominate the surface charge characteristics, leading to colloids aggregation or stabilization. In redox-dynamic environment, soil colloids and the SOM associated with minerals can be mobilized or released as iron mineral dissolution or pH shifting. However, the interactions between soil colloids and SOM and the role of mobile colloids in soil carbon cycling under different redox conditions are largely unknown. In this study, we investigate the complex dynamic interactions of colloids, carbon, and iron oxides and their implications in colloid mobilization and carbon cycling. Batch experiments were conducted to quantify and characterize mobilized soil colloids affected by addition of dissolved organic matter (DOM) under different redox conditions. Preliminary results showed that colloid release and stability were controlled by both redox conditions and addition of DOM. Under anaerobic conditions (AN) more colloids were released but settled out as experiment continued. On the contrary, under aerobic conditions (AE) although fewer colloids were released, they were more stable. Moreover, DOM affected colloid release and stability differently under AE and AN, addition of DOM facilitated colloids release under AE but resulted in decreased stability under AN. Relevant solution chemistry analysis showed that iron reduction and indigenous organic matter desorption may be responsible for colloid release and aggregation under AN. In this presentation, we will discuss the dynamic interactions between colloid release, DOM and redox conditions and the implications of colloid-facilitated transport and carbon cycling.