Mineralogical controls on soil black carbon preservation

Abstract

[1] Black carbon (BC) has long been considered a chemically resistant component of soil organic carbon (SOC). However, there is substantial evidence that the chemistry of most C compounds is less important for long-term storage than is physical protection (e.g., mineral sorption). We explored BC retention in grasslands that lie along a climate gradient that produces strong differences in short range order (SRO) minerals known to drive landscape-scale retention of SOC. We measured soil BC content using 13 C nuclear magnetic resonance (NMR) spectroscopy, and used radiocarbon dating on a subset of samples to relate BC content to long-term soil C storage. Black C concentrations in soil ranged from 0.2 to 2.9%, representing 10-30% of SOC and spanning levels found in temperate grasslands around the world. Black C concentrations were significantly correlated with SRO minerals, but the strongest single predictor of BC content was simply SOC. The ratio of BC/OC was fairly insensitive to SRO minerals, suggesting that BC responds similarly to reactive minerals as does OC. Direct links between SOC and BC retention warrant further study. We found no evidence that BC is preferentially retained relative to OC, with soil radiocarbon ages apparently driven primarily by inputs of new OC. These results indicate that physical protection may play a strong role in BC retention, and that BC cycling in soils may be more similar to OC cycling than is generally thought.

Distribution, input pathway and mass inventory of black carbon in sediments of the Gulf of Thailand, SE Asia

“…This suggests that the hydrodynamic transport and depositional mechanism could also be an important factor affecting the occurrence of BC and TOC and their relationships, especially in the open GOT. Actually, this good correlation between BC and bulk OM was not only noticed in the particle phase (e.g., in soil, Glaser and Amelung, 2003;Cusack et al, 2012) but also in the dissolved phase and has been reported worldwide (e.g., Dittmar et al, 2012;Jaffe et al, 2013;Ding et al, 2013Ding et al, , 2015. The close relationship between BC and bulk OM in the dissolved phase could indicate that the release and subsequent sorption and desorption processes of BC are a complex function of environmental factors and particle properties, just as for bulk dissolved OM , which suggests that the mobilization of BC and bulk OM in various matrices is also mechanistically coupled.…”

Environmental Dynamics of Dissolved Black Carbon in Aquatic Ecosystems

“…Recent case studies that examined the relationship between DOC and DBC as well as soil BC and soil organic matter (Cusack et al, 2012;Glaser et al, 2003) are consistent with this observation. Because the abundance distribution for DOC and DBC concentrations were not normally distributed, I grouped the samples according to their DOC concentrations into 15 groups for further statistical analysis (Fig.…”

“…Additional reasons could be differences in the soil and DOM characteristics among the wetlands. Cusack et al (2012) reported a linear correlation between soil organic carbon (SOC) and soil BC, indicating that mineralogical interactions between soil BC and minerals could preserve the BC.…”

“…However, and hydrophobic organic pollutants, where the presence of DOM serves as a mobilizing agent for otherwise insoluble compounds (Kim and Kwon, 2010). Alternative, highly aromatic, polar BC oxidation products may also strongly bind to mineral surfaces in soil (Cusack et al, 2012; and only become mobilized by DOC via exchange reactions on the mineral surface. As such, molecular characteristics of the "mobilizing reagent" DOM may also be critical in this process.…”

“…It is ubiquitous in the environment, where it slowly decomposes , but part of it is preserved for thousands of years . Global biomass burning generates 40-250 Mt BC per year , and 5-40% of total soil organic carbon is estimated to be BC (Cusack et al, 2012;Masiello and Druffel, 2003;Skjemstad et al, 2002).…”