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Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily--and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming., Understanding soil biogeochemistry is essential to the stewardship of ecosystem services provided by soils, such as soil fertility (for food, fibre and fuel production), water quality, resistance to erosion and [...]

The adoption of land management strategies which promote the storage of carbon (C) as soil organic matter has been identified as one means to lower the atmospheric concentration of C [...]

Researchers from the University of Waterloo, Ontario, used solid-phase microextraction to examine the concentration levels of the adsorption of very hydrophobic organic compounds onto poly(dimethylsiloxane) fiber coatings and dissolved humic organic matter.

The purpose of this study is to create a conceptual and methodological framework to understand the role of Humic substances[HS] in environmental processes. HS are a naturally occurring mix of compounds that play a crucial role in pollutant chemistry. The molecular weight of an HS determines its binding properties, pollutant partitioning, adsorption onto minerals, and behavior during water treatment. A log-normal distribution model of aquatic fulvic acid is created and compared to HP-SEC measurements. Despite caveats the model is useful, further comparisons will be done between the model and whole water and soil, and more conceptualization will be needed to assimilate metal and organic speciation data.

Almost 84% of the initially applied radioactivity immobilized in different fractions was determined after 9 weeks of anaerobic-aerobic incubation with an optimized experimental setup. On the other hand, 57% of the radioactivity was determined as immobilized in the soil organic matrix after 5 weeks of anaerobic treatment. Humic acid and fulvic acid fraction yielded small amounts of radioactivity after alkaline hydrolysis of the solvent-extracted soil/molasses mixtures was undertaken.

Electron spin resonance spectroscopy and nuclear magnetic resonance studies indicate that under acidic pH humic substances reduce vanadium (V) to vanadium (IV), with the vanadium(IV) ion bound to the oxygen donor at the carboxylic acid sites of the humic substances. At neutral pH, vanadate is stabilized with its binding to humic substances. The binding of vanadium to humic substances is determined by the concentration of vanadium and the pH of the medium.

Aromatic acids and other small natural organic molecules appear to govern the fate, transport and bioavailability of anthropogenic organic compounds in the environment by occupying and hindering the adsorption sites in soil organic matter (SOM). The selected five aromatic acids namely vanillic, ferulic p-hydroxybenzoic acid, trans-cinnamic and p-coummaric acids yielded nonlinear isotherms yielded nonlinear isotherms, revealing a distribution of site energies in SOM.

The attenuated total reflectance Fourier-transform infrared spectroscopy and molecular orbital calculation were utilized to analyze the chemical bonding between salicylic acid and illite clay. The study was undertaken to understand how organic molecules are absorbed by natural organic matter and subsequently absorbed by the soil. Results showed a monodentate complex is formed at neutral pH between the salicylate anions and the Al3+ octahedra at the illite clay edges, and a bidentate complex at lower pH between the carboxylate oxygen atoms and two vicinal Al3+ octahedra.

The total luminescence spectra of humic substances from the International Humic Substances Society were determined using a spectrofluorometer. Data indicated variations in the spectra between soil-derived and aquatic-derived IHSS humic substances and between soil- and aqueous-derived humic and fulvic acids. The changes in pH were found to have significant effects on the substances' fluorescence spectral characteristics. In contrast, ionic strength of the humic substances had no significant effect on their spectra.

The impact of ozone on the colloidal stability and aggregation of particles coated with natural organic matter (NOM) was investigated. The results showed that ozone caused particle destabilization when calcium was present. It is suggested that this ozone-induced destabilization was due to the increase in calcium association with ozonated NOM constituents or the production of more ligand sites.

The surface area, porosity and diffusion mechanisms of three different soil organic matter samples were studied. It was shown that the diffusion coefficient of CO2 was affected by the cross-linking density of the matrix. Sample hydration did not have much effect on the microporous structure. The results indicated that configurational diffusion was the primary transport mechanism of nonionic organic contaminants in the samples.

The effect of natural organic matter on polycyclic aromatic hydrocarbons in aquifer sediments was investigated. The results showed that natural organic matter had a substantial facilitating effect on transport while enhancing the desorption of polycyclic aromatic hydrocarbons in aquifer sediments. This effect was observed to be greater in the case of hydrophobic polycyclic aromatic hydrocarbons.

Pentachlorophenol (PCP) adsorption and mobility in water-saturated soil columns was quantified through kinetic, transport, and equilibrium experiments. Results showed that natural dissolved organic matter (NDOM) does not influence the PCP adsorption rate on soil at a hydrogen-ion concentration (pH) of 5.4 and 6.3 and minimally affects isotherm parameter estimates at pH 5.2, 5.4 and 6.1. It was concluded that NDOM does not induce nor inhibit PCP adsorption and transport in soil columns under conditions found in groundwater-soil systems exposed to nonpoint source contamination.

An understanding of the chemical and physical properties of whole water organic matter is central to the characterization of the role such humic substances play in the fate and reactivity of organic pollutants. Size exclusion chromatographic experiments are conducted on several fulvic acids, an industrial humic acid and various organic matter to determine their respective spectroscopic and physical properties.

Analytic pyrolyis is a research method used in the examination of the structural properties of complex macromolecular materials. The application of this method to the study of humic substances, however, is limited by the numerous pitfalls that arise as a result of procedural problems caused by thermal reactions, pyrolysis unit configuration and chromatographic inaccuracy. Possible solutions to these methodological problems are discussed.

Sorption of organic matter to mineral surfaces controls lability and quantity of organic matter in marine sediments, stabilizes component molecules and diminishes their remineralization rates. Hence, internally labile molecules such as amino acids and simple sugars are preserved in marine deposits by sorption, which correlates organic carbon preservation in marine sediments to mineral surface deposition.

The enzymatic joining of the pollutant (2,4-dichlorophenol, 2,4-DCP) to humic material is exposed through an NMR technique that uses 2,4-DCP labeled with 13C in combination with broad-band decoupled 13C NMR. The 13C labeling NMR technique which is extensively discussed allows for the direct examination of bonding between the pollutant and a complex macromolecular structure. The NMR technique may be expanded to other pollutants.

The impact that water saturation has on the solute partition in soil organic matter (SOM) was studied. Sorption data on benzene, carbon tetrachloride and trichloroethylene were obtained. Florida peat and Michigan muck, soils with a high organic content, were used. The research indicates that the partition in the SOM is the primary process in the uptake of the three volatile organic liquids. The suppression of adsorption by minerals is more dominant than the mitigation of the partition effect in SOM.

Assimilation of soil organic matter and fresh plant debris by Millsonia anomala, a tropical geophagous earthworm, was investigated by measuring changes in the [sup.13.C/sup.12.C] ratio of their tissues when fed on organic matter naturally labelled by [13.sup.C]. Individuals collected from a soil colonized by [C.sup.4] plants ([C.sup.4] soil) that were fed on [C.sup.3] soil had >50% of tissue C derived from the [C.sup.3] soil after 33 d. Assimilation of organic matter associated with different particle size fractions was investigated with individuals fed for 25 d on [C.sup.4] soil with [C.sup.4] particle size fractions substituted in turn for the equivalent [C.sup.3] soil particle fraction. A significant labelling of earthworms was observed with both the 250-200 [mu]m and the 0-20 [mu]m particle size fractions. Addition of fresh [C.sub.3] plants debris to the [C.sup.4] soil also resulted in a significant change in earthworm C isotope ratio. Assimilation of fresh plant material was greater than that of soil organic matter. This shows that young M. anomala are able to assimilate young organic matter (fresh plant debris, course oil organic matter) as well as fine soil organic matter, both of which classically have been regarded as strongly resistant to decomposition in models of soil organic matter dynamics. Key words: assimilation; C isotope ratio; fresh plant debris; geophagous tropical earthworm; particle size organic fractions; soil organic matter.

Earthworms represent the dominant fraction of soil macroinvertebrate biomass in Kansas tallgrass prairie and thus may have a large impact on nutrient budgets. To evaluate this impact I estimated cast production and rates of nutrient processing by the native genus Diplocardia and by exotic Lumbricidae in permanent plots on two soil types at Konza Prairie Research Natural Area. Total cast production was estimated from field population estimates, soil climate data, and cast production-temperature relationships obtained in the laboratory. The organic matter and mineral N and P contents of surface casts by month were used to estimate total processing of these substances in the field. Earthworms present in the study sites were Diplocardia longiseta, D. kansensis, D. rugosa, D. singularis, D. smithii, D. verrucosa, and the European species Aporrectodea caliginosa and Octolasion cyaneum. Estimated total cast production and nutrient processing by Diplocardia spp. exceeded that of exotics in both soil types, in spite of higher populations of Lumbricidae in one soil. Total annual soil consumption by all earthworms was 4-10% of the A-horizon, depending on soil type. Organic matter equivalent to 10% of total soil organic matter in the top 15 cm or to 100-300% of plant annual belowground production appears to pass through the earthworms each year. Mineral N processed was [is approx. =] 10-12% of annual plant N uptake, comparable to half of the input from precipitation, while the P processed was equivalent to 50% of annual uptake. In contrast to other grassland systems studied, the introduction of Lumbricidae had a negative effect on soil turnover and nutrient mineralization due to the lower throughput of Lumbricidae and their relative intolerance of summer soil temperatures.

We evaluated the importance of dissolved organic matter as a vehicle for the movement of N and P from the canopy and the forest floor into the mineral soil of a deciduous forest. We also examined the origin and nature of dissolved organic matter from the forest floor to see whether it was simply soluble plant material or highly humified matter. The average annual output from the forest floor in the form of dissolved organic matter was 18, 28, and 14% of the input in solid litterfall for C, N, and P, respectively. In throughfall, about half of the dissolved N and P was organic. But, in solution percolating from the forest floor, 94% of the N and 64% of the P was organic. Leaching from the forest floor was not a source of inorganic N and P for the mineral soil. Instead, the forest floor was a sink for the removal of these inorganic nutrients delivered in throughfall. Microbial immobilization was the most likely explanation for much of the inorganic nutrient removal. In contrast, the forest floor was an abundant contributor of N and P to the mineral soil in the form of dissolved, and possibly particulate, organic matter. Much of the dissolved organic matter entering the A horizon originated from the upper (Oa and Oe horizon) forest floor, but it was modified in several respects compared to the original soluble material. The solution percolating from the forest floor over most of the year was much richer in nitrogen, contained a much larger proportion of hydrophilic acids, and contained a much smaller proportion of carbohydrate-rich hydrophilic neutrals, than did the original water-extractable material in autumn litter. However, the fresh autumn litter did contain a similar proportion of soluble hydrophobic acids that resembled dissolved humic substances in several respects. Most of the flux of nitrogen from the forest floor to the A horizon was carried by humic substances and highly colored hydrophilic acids.