Black Carbon (BC) may significantly affect nutrient retention and play a key role in a wide range of biogeochemical processes in soils, especially for nutrient cycling. Anthrosols from the Brazilian Amazon (ages between 600 and 8700 yr BP) with high contents of biomassderived BC had greater potential cation exchange capacity (CEC measured at pH 7) per unit organic C than adjacent soils with low BC contents.Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy coupled with scanning transmission X-ray microscopy (STXM) techniques explained the source of the higher surface charge of BC compared with non-BC by mapping crosssectional areas of BC particles with diameters of 10 to 50 mm for C forms. The largest cross-sectional areas consisted of highly aromatic or only slightly oxidized organic C most likely originating from the BC itself with a characteristic peak at 286.1 eV, which could not be found in humic substance extracts, bacteria or fungi. Oxidation significantly increased from the core of BC particles to their surfaces as shown by the ratio of carboxyl-C/aromatic-C. Spotted and non-continuous distribution patterns of highly oxidized C functional groups with distinctly different chemical signatures on BC particle surfaces (peak shift at 286.1 eV to a higher energy of 286.7 eV) indicated that non-BC may be adsorbed on the surfaces of BC particles creating highly oxidized surface. As a consequence of both oxidation of the BC particles themselves and adsorption of organic matter to BC surfaces, the charge density (potential CEC per unit surface area) was greater in BC-rich Anthrosols than adjacent soils. Additionally, a high specific surface area was attributable to the presence of BC, which may contribute to the high CEC found in soils that are rich in BC.

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Black Carbon Increases Cation Exchange Capacity in Soils

Communities of microscopic plant life, or phytoplankton, dominate the Earth's aquatic ecosystems. This important new book by Colin Reynolds covers the adaptations, physiology and population dynamics of phytoplankton communities in lakes and rivers and oceans. It provides basic information on composition, morphology and physiology of the main phyletic groups represented in marine and freshwater systems and in addition reviews recent advances in community ecology, developing an appreciation of assembly processes, co-existence and competition, disturbance and diversity. Although focussed on one group of organisms, the book develops many concepts relevant to ecology in the broadest sense, and as such will appeal to graduate students and researchers in ecology, limnology and oceanography.

/pdf/the-ecology-of-phytoplankton-4ev70n3jsq.pdf

The Ecology of Phytoplankton

The response of soil organic matter (OM) decomposition to increasing temperature is a critical aspect of ecosystem responses to global change The impacts of climate warming on decomposition dynamics have not been resolved due to apparently contradictory results from field and lab experiments, most of which has focused on labile carbon with short turnover times But the majority of total soil carbon stocks are comprised of organic carbon with turnover times of decades to centuries Understanding the response of these carbon pools to climate change is essential for forecasting longer-term changes in soil carbon storage Herein, we briefly synthesize information from recent studies that have been conducted using a wide variety of approaches In our effort to understand research to-date, we derive a new conceptual model that explicitly identifies the processes controlling soil OM availability for decomposition and allows a more explicit description of the factors regulating OM decomposition under different circumstances It explicitly defines resistance of soil OM to decomposition as being due either to its chemical conformation (quality )o r its physico-chemical protection from decomposition The former is embodied in the depolymerization process, the latter by adsorption/desorption and aggregate turnover We hypothesize a strong role for variation in temperature sensitivity as a function of reaction rates for both We conclude that important advances in understanding the temperature response of the processes that control substrate availability, depolymerization, microbial efficiency, and enzyme production will be needed to predict the fate of soil carbon stocks in a warmer world

https://www.fs.fed.us/rm/pubs_other/rmrs_2011_conant_r001.pdf

Temperature and soil organic matter decomposition rates – synthesis of current knowledge and a way forward

A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization−mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic...

Molecular Structure in Soil Humic Substances: The New View

Chars originating from the burning or pyrolysis of vegetation may significantly sorb neutral organic contaminants (NOCs). To evaluate the relationship between the char composition and NOC sorption,...

Compositions and sorptive properties of crop residue-derived chars.

The compositions of humic acids (HAs) from various Histosols in North America and Europe, of similarly treated plant-extracted materials (PEMs), of coal-extracted humic acids, and of International Humic Substances Society (IHSS) Florida peat were quantified by solid-state 13 C nuclear magnetic resonance (NMR). In order to obtain quantitative intensities, the peak areas in direct-polarization 13-kHz magic-angle spinning (DPMAS) 13 C NMR spectra were corrected for incomplete relaxation by factors measured in cross-polarization spin-lattice relaxation time (CP/T 1 ) experiments with total sideband suppression (TOSS). The elemental compositions (%C, %H, %O + N) of a peat sample, 8 HAs and 2 PEMs were estimated from the NMR results and compared with chemical analyses, as well as solution NMR for two of the HAs. The results are in good agreement, which shows that DPMAS corrected by CP/T 1 -TOSS permits quantitative characterization of HAs and PEMs. The compositions of the PEMs deviate significantly from those of the Histosol HAs. The compositions in terms of nine types of chemical groups were computed. The investigated HAs consist of more than 60% of aromatic and CO carbons (including both carbonyl and carboxyl groups). Previous cross-polarization magic-angle spinning (CPMAS) NMR experiments have significantly underestimated the ratio of sp 2 -to sp 3 -carbons; in particular, the true COO carbon fraction is a factor of two larger than estimated by CPMAS NMR. In spite of their wide range of geographical origins, the compositions of the Histosol HAs appear to be relatively uniform, suggesting that the search for a general model of Histosol HA structure is worthwhile. Eight models proposed in the literature do not reproduce the experimentally determined compositions, but a few models show promising partial agreement.

Quantitative Characterization of Humic Substances by Solid-State Carbon-13 Nuclear Magnetic Resonance

Analytical and thermodynamic data, EPR, FTIR, solution 1H and solid-state 13C cross polarization magic angle spinning NMR and solid-state extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra have been recorded for purified humic acids (HAs) isolated from a German peat (GHA), an Irish peat (IHA), an unpolluted New Hampshire bog soil (NHA) and their tightly bound copper(II), iron(III) and manganese(II) forms. Brief water washing of partly or fully metal-loaded HAs leaves ‘tightly’ bound metal in the isolated freeze-dried solids. Most of this metal is removed by washing with 0.1 M HCl, indicating acidic HA functional groups as principal metal binding sites. The number of nearest-neighbour atoms co-ordinated to tightly bound CuII (four), FeIII (six, probably with distorted geometry) and MnII (six, undistorted) in solid GHA, IHA and NHA were determined by XANES and EXAFS spectroscopy with reference standards. Isotherms measured at 20.0 °C and pH 2.4–3.2 with [M]total = 0.18–25.8 mM for tight, reversible Cu2+(aq), Fe3+(aq), and Mn2+(aq) binding by solid IHA and NHA fit the Langmuir model and give the pH-independent stoichiometric site capacities νi and equilibrium constants Ki for metal binding at specific HA sites i = A, B and C. Tight binding sites A, B and C of IHA are occupied by CuII, sites A and B by FeIII and site A by MnII, while only identical metal binding site A in NHA is tight enough to resist metal removal by brief water washing. A new helical HA molecular model based on the empirical formula C36H30N2O15·xH2O visualizes metal binding and the likely roles of HAs in biomineralization. Site A is suggested to be carboxylate, mixed ligands probably constitute site B, and site C is tentatively assigned as the interior of the HA helix. Binding free energies and EPR evidence suggest that Cu2+(aq), Fe3+(aq) and Mn2+(aq) rapidly transfer between specific HA binding sites. This affects rates of metal release and transfer to minerals.

Tight metal binding by humic acids and its role in biomineralization

History, Philosophy and Spectroscopy Data, Mobility and Stability Masses, Similarities and Properties Models and Theories Images, Oxidation and Humification Organic Ores and Analysis of Commercial HSs Plant Growth Stimulation and Antimutagenesis Subject Index.

Humic substances : structures, models and functions

The properties of humic substances in plants, soils and sediments regulate the environment and affect all aspects of life, yet they are nature's least understood materials Current work in this field in the late-1990s applies front-line instruments and techniques to solve the 200-year old mystery of humic substance structures and their relationships to macro- and microscopic properties This book highlights environmental processes from a molecular viewpoint, focusing on the use of chemical and physical methodology to explain this complex subject matter and emphasizing up-to-date research It covers aspects of biology, chemistry, physics and physiology of humic substance macromolecules, includes the very latest in high level molecular modelling and teaches techniques of particular relevance to agriculture and agronomy

Elham A. Ghabbour

Papers

Quantitative Characterization of Humic Substances by Solid-State Carbon-13 Nuclear Magnetic Resonance

Tight metal binding by humic acids and its role in biomineralization

Humic substances : structures, models and functions

Humic substances : structures, properties and uses

Spectroscopic characterization of humic acid fractions isolated from soil using different extraction procedures