Pedogenic Inorganic Carbonates in Alabama Blackland Prairie Soils.

The origin and fate of pedogenic inorganic carbonates (PICs) is an important part of the global carbon cycle. Pedogenic carbonates form mostly under arid to sub-humid conditions, however, carbonates in the lower solum of Alabama-Mississippi Blackland Prairie soils (mostly Vertisols) forming over Cretaceous chalks appear to be pedogenic. Suspected pedogenic carbonate forms include soft and cemented masses as coatings and infillings. The determination of the occurrence and abundance of inorganic carbonates in these pedogenic environments can further understanding of the C cycle and storage in soils. In this study, inorganic carbonates from two pedons representing common soils of this region, a Rendollic Eutrudept and an Oxyaquic Hapludert, were characterized and quantified. Pedogenic and lithogenic carbonate forms were differentiated using micromorphological, isotopic, and elemental (e.g. rare earth) analyses. Carbonate quantities in the Hapludert and Eutrudept ranged from 8 to 43% and 52 to 62%, respectively. Significant differences (p ≤ 0.05) exist between the mean isotopic C values (δ¹³C) of pedogenic soft masses, nodules, and lithogenic samples. Significant differences were also found between light rare earth element concentrations of pedogenic and lithogenic carbonate forms, but as shown in other studies, heavy rare earth elemental concentrations did not differ significantly. Using multiple lines of evidence, significant pedogenic carbonates have been identified in these Blackland Prairie soils.