Carbon sequestration in iron-nodules in moist semi-deciduous tropical forest soil

Abstract

Soil organic carbon (SOC) in tropical forest soils is typically characterized by fast turnover rates but mineralization might be inhibited resulting in long term organic matter protection. This study focuses on SOC trapped in iron oxides in a Paleudult (chromic Acrisol) located in the moist semi-deciduous forest in Ghana by determining the age of the SOC, quantifying the geochemical characteristics of the SOC, and estimating how much of the SOC that is bound so tightly to the oxides that it does not participate in the normal turnover of organic matter in the soil. The SOC has been characterized by using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and 14C dating. The turnover rate of the reactive SOC was determined by basal soil respiration (BSR) and a ratio between the SOC stock in the soil. The investigation shows that SOC associated with iron nodules has a 14C age of more than 21,000 years and the absence of CO2 release during BSR measurements reveals that iron nodules have trapped and immobilized ~ 21% of SOC stored in the top 1 m (~ 3.4 kg C m− 2). NMR results indicate that trapped SOC in the iron nodules is more decomposed than the organic matter in the topsoil.