Erosional distribution of metal oxides and its implication for soil carbon dynamics

Abstract:

Iron (Fe) and Aluminum (Al) oxides are common minerals in the soil system that can constitute 0.5 to 50% of soil mass. Fe and Al oxides occur in both crystalline and poorly crystalline forms, typically as <150nm in diameter nano-particles that have high specific surface area, high degree of hydration, and are very reactive with a variable charge. Fe and Al oxides have a tendency to form strong organic matter (OM)-mineral bonds through anion and inner-sphere ligand exchange reactions that enable them to be critical for persistence of OM in the soil system. Currently, we lack basic measurements and understanding of rates of lateral distribution of metal oxides with soil erosion; factors regulating transport of reactive soil minerals; and its implications for SOM dynamics. In this study, we determined concentration in soils and the rate of sediment and carbon erosional export from catchments within the Kings River Experimental Watersheds of California (Sierra National Forest in the southern part of the Sierra Nevada). In addition, we determined soil concentrations and rate of erosion of three classes of Fe and Al oxides (total pedogenic Fe, poorly crystalline Fe and Al oxides, and Fe and Al complexed with organic matter). Our results show that considerable variability exists in the concentration and transport rates of Fe and Al oxides in the study watersheds, but slope is strongly associated with rate of oxide transport across the three years (2009-2011) that we studied. We also found that the crystalline and poorly crystalline species of Fe and Al were transported at higher rates than the metal oxides that were complexed with iron oxides.