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• Chemical and thermal analyses of fractions from 75 soils were cross-correlated. • Observed strong correlations between broad thermal regions and chemical types. • EGA data generated stronger correlations with NMR than did DSC. • Demineralization treatments resulted in substantial differences in correlations. • Bioenergetics may be better approach than chemical composition for SOM reactivity. While many advanced analytical methods have been applied to soil organic matter (SOM), its highly complex and heterogeneous chemical composition still eludes complete characterization. Analytical thermal analysis has been proposed as a relatively rapid, inexpensive method for SOM characterization that requires no pre-treatment, but is challenging due to a lack of direct information about chemical composition. The goal of this study was to inform the interpretation of coupled differential scanning calorimetry and evolved gas analyses (DSC, CO2-EGA) using spectral correlations with solid phase 13C NMR data. We used a subset of soils collected as part of the Australian National Soil Carbon Research Program (SCaRP), which were physically fractionated and characterized using conventional analytical methods. Correlating the well-understood NMR spectra with the less-understood DSC and CO2-EGA thermograms provided some indications of which chemical compounds combust at which temperatures. Overall, the EGA data generated stronger correlations compared to correlations with DSC data, which was attributable to greater variability in DSC data due thermal reactions associated with minerals. Direct comparison of NMR and thermal data for the mineral associated organic matter in the fine (<50 µm) fraction was not possible due to the need to demineralize samples prior to NMR analyses. Thermal analyses showed substantial differences in samples pre- and post-HF pretreatment, and the NMR data for HF treated samples showed scattered and weak correlation patterns with DSC and EGA data for untreated samples. While precise chemical compositions cannot be gleaned directly from thermal analyses results, thermal approaches provide an avenue of investigation into SOM reactivity based on bioenergetics that may be a quantitative representation of SOM persistence. [ABSTRACT FROM AUTHOR]

The rarity of rapid campaigns to characterize soils across scales limits opportunities to investigate variation in soil carbon stocks (SOC) storage simultaneously at large and small scales, with and without site-level replication. We used data from two complementary campaigns at 40 sites in the United States across the National Ecological Observatory Network (NEON), in which one campaign sampled profiles from closely co-located intensive plots and physically composited similar horizons, and the other sampled dozens of pedons across the landscape at each site. We demonstrate some consistencies between these distinct designs, while also revealing that within-site replication reveals patterns and predictors of SOC stocks not detectable with non-replicated designs. Both designs demonstrate that SOC stocks of whole soil profiles vary across continental-scale climate gradients. However, broad climate patterns may mask the importance of localized variation in soil physicochemical properties, as captured by within-site sampling, especially for SOC stocks of discrete genetic horizons. Within-site replication also reveals examples in which expectations based on readily explained continental-scale patterns do not hold. For example, even wide-ranging drainage class sequences within landscapes do not duplicate the clear differences in profile SOC stocks across drainage classes at the continental scale, and physicochemical factors associated with increasing B horizon SOC stocks at continental scales frequently do not follow the same patterns within landscapes. Because inferences from SOC studies are a product of their context (where, when, how), this study provides context—in terms of SOC stocks and the factors that influence them—for others assessing soils and the C cycle at NEON sites. [ABSTRACT FROM AUTHOR]

Seagrass meadows store globally-significant quantities of organic 'blue' carbon. These blue carbon stocks are potentially vulnerable to anthropogenic stressors (e.g. coastal development, climate change). Here, we tested the impact of oxygen exposure and warming (major consequences of human disturbance) on rates of microbial carbon break-down in seagrass sediments. Active microbes occurred throughout seagrass sediment profiles, but deep, ancient sediments (~5000 yrs. old) contained only 3% of the abundance of active microbes as young, surface sediments (<2 yrs. old). Metagenomic analysis revealed that microbial community structure and function changed with depth, with a shift from proteobacteria and high levels of genes involved in sulfur cycling in the near surface samples, to a higher proportion of firmicutes and euraracheota and genes involved in methanogenesis at depth. Ancient carbon consisted almost entirely (97%) of carbon considered 'thermally recalcitrant', and therefore presumably inaccessible to microbial attack. Experimental warming had little impact on carbon; however, exposure of ancient sediments to oxygen increased microbial abundance, carbon uptake and sediment carbon turnover (34–38 fold). Overall, this study provides detailed characterization of seagrass blue carbon (chemical stability, age, associated microbes) and suggests that environmental disturbances that expose coastal sediments to oxygen (e.g. dredging) have the capacity to diminish seagrass sediment carbon stocks by facilitating microbial remineralisation. Unlabelled Image • Seagrass ecosystems store globally-significant amounts of blue carbon • Mechanisms underpinning blue carbon destabilisation are largely unknown • Exposure of blue carbon to oxygen triggered microbial remineralization • Sediment carbon turnover increased 34–38-fold following oxygen exposure • Activities that expose seagrass sediments to oxygen threaten blue carbon stability [ABSTRACT FROM AUTHOR]

Sorption of organic carbon (OC) to phyllosilicate clays and hydrous iron oxides retards its mineralization, thus contributing to stabilization of organic carbon in soils. The degree of protection varies with the nature of the minerals present. In a previous study, we reported that when the amount of OC exceeds the sorption capacity of minerals, the rate of OC mineralization is determined primarily by mineral surface area. Here, we report on OC mineralization under conditions of less OC loading and with OC pre-sorbed to the mineral surfaces. The same suite of minerals (kaolinite, illite and smectite with and without goethite coating and illite coated with haematite, goethite and ferrihydrite) was used as in the previous study. The stability of sorbed OC decreased in the order kaolinite>illite>smectite amongst the uncoated clays. Goethite coating of kaolinite and smectite increased the stability of sorbedOMagainst microbial decomposition, while the stability of illite-associated OC did not change with goethite coating. For illite coated with different hydrous iron oxides, only ferrihydrite increased the stability of sorbed OC against microbial decomposition. These differences reflect closely the differences in the strength and reversibility of OC sorption, as measured in previous batch sorption experiments on these systems, rather than reflecting differences in mineral surface area. These findings demonstrate that at relatively small loadings of OC, the degree of protection of sorbed OC provided by mineral surfaces is controlled primarily by the strength of organo-mineral associations. [ABSTRACT FROM AUTHOR]

Abstract: Sorption of organic carbon onto phyllosilicate clays and hydrous iron oxides influences the accumulation and stabilisation of organic carbon in soils. However, the effects of interactions between hydrous iron oxides and phyllosilicate clays on the sorption of dissolved organic carbon (DOC) are poorly understood. We carried out a batch experiment to examine the effects of goethite coatings on kaolinite, illite, and smectite on DOC sorption. The effect of coating illitic clay with different hydrous iron oxides (haematite, goethite, ferrihydrite) on DOC sorption was studied in another experiment. Organic matter extracted from dried medic (Medicago truncatula cv. Praggio) shoot residue was reacted with minerals at DOC concentrations ranging from 0 to 200mgCL−1 at pH6.0. The maximum adsorption capacity (Qmax ) of phyllosilicate clays, as determined from fits to the Langmuir equation, increased in the order kaolinite

Abstract: Stabilisation of soil organic carbon (SOC) is known to be affected by chemical adsorption of organic carbon onto clay minerals and iron or aluminium hydrous-oxides. However, little information is available on the relative effects of different clay minerals in the presence or absence of different hydrous oxides. We examined organic carbon stabilisation in an incubation experiment involving kaolinitic, illitic and smectitic clays with and without added goethite. The effect of adding hydrous iron (Fe) oxides (goethite, haematite, ferrihydrite) or imogolite to illitic clay only was studied in another experiment. Carbon (C) mineralisation, measured continuously over a 144-day incubation, was significantly influenced by clay mineralogy, with higher rates observed in the presence of the kaolinitic than the illitic or smectitic clays. The presence of goethite reduced C mineralisation in kaolinitic clay treatments but did not affect C mineralisation for illitic and smectitic clay treatments. With regard to the influence of different hydrous oxides, only addition of ferrihydrite to illitic clay reduced C mineralisation. The dynamics of C mineralisation over the course of the incubation were also studied; a two-pool model consisting of slowly and rapidly decomposing C pools provided a better fit than did a one-pool model. We introduce a novel approach to a problem associated with such two-pool fits: identifying when the incubation is long enough for the fitted variables to be reliable. Based on an analysis of two-pool model variables, we identified that SOC stabilisation in our systems was brought about by a decrease in the size of decomposable pools rather than a decrease in the rates of decomposition of either pool. This implies that on sorption, a portion of the organic matter is strongly protected from decomposition. [Copyright &y& Elsevier]

Australia's tidal marshes have suffered significant losses but their recently recognised importance in CO2 sequestration is creating opportunities for their protection and restoration. We compiled all available data on soil organic carbon (OC) storage in Australia's tidal marshes (323 cores). OC stocks in the surface 1 m averaged 165.41 (SE 6.96) Mg OC ha−1 (range 14-963 Mg OC ha−1). The mean OC accumulation rate was 0.55 ± 0.02 Mg OC ha−1 yr−1. Geomorphology was the most important predictor of OC stocks, with fluvial sites having twice the stock of OC as seaward sites. Australia's 1.4 million hectares of tidal marshes contain an estimated 212 million tonnes of OC in the surface 1 m, with a potential CO2-equivalent value of $USD7.19 billion. Annual sequestration is 0.75 Tg OC yr−1, with a CO2-equivalent value of $USD28.02 million per annum. This study provides the most comprehensive estimates of tidal marsh blue carbon in Australia, and illustrates their importance in climate change mitigation and adaptation, acting as CO2 sinks and buffering the impacts of rising sea level. We outline potential further development of carbon offset schemes to restore the sequestration capacity and other ecosystem services provided by Australia tidal marshes. [ABSTRACT FROM AUTHOR]

Human myiasis is a rare condition. It is more common in tropical regions. Umbilical cord myiasis has not previously been reported from a temperate climate, for example, New Jersey. We report a 9-day-old infant with umbilical cord myiasis. The maggots were identified by the entomologist as the larvae of Sarcophagidae, more commonly known as flesh flies. [ABSTRACT FROM AUTHOR]