PNNL

Abstract

It is well-recognized and documented in the literature that a considerable fraction of the soil organic matter (SOM) is associated with Fe-oxide minerals. Recent studies have also showed that the persistence of various classes of SOM may depend on soil Fe mineralogy. Other laboratory studies with model mineral-associated organic matter (MAOM) moieties, which were primarily focused on the short-range ordered (SRO) Fe-mineral, such as ferrihydrite, either coated or co-precipitated with natural organic matter (NOM) have suggested that the mineral phase transformation and adsorption/desorption of SOM is rather complex, but appears to be largely controlled by the C/Fe ratio of the MAOM moiety and geochemical conditions. It’s also clear from multiple recent studies that the nature or type of SOM (microbial vs. plant-derived) adsorbed on mineral surfaces, and the rate and extent of SOM bio-degradation depend on the type of mineral (e.g., ferrihydrite, Fe-containing phyllosilicate minerals, calcite), and/or metal ions (e.g., Al, Fe, and Ca), that are associated with the SOM. Modeling studies that are primarily centered on achieving a better understanding of the effect of mineral type on SOM interactions with minerals and degradation are also reported. These studies have improved the understanding of the nature and stability of MAOM in soils of varying types and under different conditions, positioning researchers to better predict the properties and stabilities of organo-mineral associations in soils. This special section includes a collection of studies that span across modeling efforts, modeling coupled with experimental studies, laboratory experimental studies on ferrihydrite-SOM systems that are subjected to anoxic conditions, a study that focused on the effect of temperature on C/Fe ratio of the ferrihydrite-SOM moieties, a laboratory study on the role of adsorbed extracellular polymeric substance (EPS) on acidity of selected soils, a study that used a tropical humid soil enriched in nanogoethite subjected to anaerobic conditions, and a study with a large set of soils from the National Ecological Observatory Network (NEON) subjected to selective chemical extractions to correlate extractable metal and SOM contents.