Carbon Fractions in Subsiding Histosols in the Everglades Agricultural Area.

Drainage of organic soils located in the Everglades Agricultural Area (EAA) started in the early 1900s and has resulted in soil loss and subsidence due to organic matter oxidation. Subsidence rates in the EAA have been reduced compared to rates reported in the 1950s and 1970s. Increased mineral content, best management practices, and recalcitrant carbon fractions may be contributing to the reduction in subsidence rates of these organic soils. The purpose of this research is to determine and characterize labile and recalcitrant soil C pools is shallow and deeper EAA soils. We hypothesize that shallow soils will have higher recalcitrant C and mineral content compared to deeper soils. Soils of the Pahokee, Lauderhill and Dania soil series (Lithic Haplosapris, Euic, Hyperthermic) were collected south and north of the EAA. Soils collected south (shallow) have average soil depths of 25 cm, whereas soils collected north (deeper) have average soil depths of 80 cm. Collected soils were separated in increments 0-10 cm, 10-30 cm, and 30-60 cm (if applicable). The labile and recalcitrant carbon pools of the soils will be determined following a fractionation procedure involving hot water and acid extraction. Selected samples will be analyzed by solid State ¹³C Nuclear Magnetic Resonance (NMR) to characterize the carbon pool of the soil. Preliminary results indicate that shallow soils have higher mineral content compared to deeper soils (32% compared to 21% respectively), as well as a higher pH (7.4 compared to 7.1 respectively). Soils corresponding to the 10-30 and 30-60 cm increments have higher pH and mineral content compared soils from the 0-10 cm increment. The changes of C pools with different soil depths will be useful to assist in the prediction of soil subsidence in the EAA and possible management practices to slow down the subsidence process.