Effect of Clay Chemistry and Particle Size Distribution on Carbon Storage from Two Forest Types in Piedmont Soils in the U.S.

In most soils, there is a general positive correlation between clay and carbon content laterally through the landscape. Clay serves to both physically and chemically protect carbon from decompositional processes. However, in some of the highly weathered, naturally acidic soils, such as those located in the southern Piedmont area of the U.S., these trends do not necessarily hold true. We conducted two transects through a clay-rich soil dominated by montmorillonite and another through a soil dominated by non-active clays and iron oxides, in order to compare trends in both particle size distributions and carbon and nitrogen content, using both a laser particle size distribution system and an elemental analyzer. The montmorillonite-rich soils contain a higher pH due to the alkaline nature of the parent rock (gabbro) and reveal a negative correlation between clay content and carbon storage. The trends also hold true for the non-active clay soils, suggesting that the negative correlations are not necessarily linked to clay chemistry. The absence of a difference in nitrogen and carbon percentages within the different clays proves to be significant, because it shows that the clay chemistry is not solely responsible for a positive correlation between clay and carbon content. These results reiterate the complexity of carbon storage processes within the Piedmont soil system.