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This study aimed at investigating the potential of x-ray photoelectron spectroscopy (XPS) for investigating soil organic matter at secondary soil particles. The XPS was applied to microaggregates of the A horizon of a Typic Haplustoll (53-[micro]m maximum real diameter) and to the fine-earth fraction (

Concentrations and forms of Al and heavy metals in aggregate core and surface fractions of forest soils in Central Europe differ significantly. The objectives of this study were to (i) test if there is a similar small-scale metal heterogeneity in topsoils of the native North American prairie and (ii) investigate the influence of climatic parameters on this heterogeneity. Aggregates of eight A horizons along a climatic transect in the North American prairie were separated into core and 0.5-mm-thick surface fractions. Seven forms of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn were determined in the aggregate fractions using a sequential extraction procedure. The differences of metal concentrations between aggregate surface and core fractions are 1 to 25% of the total concentrations of the core fractions. The percentages of easily extractable metals are up to 120% higher in the aggregate surface than in the core fractions. The percentages of the mainly silicate-bound metals (extractable only with strong acids) are up to 25% lower than in the core fractions. These results support the hypotheses that (i) preferential weathering of aggregate surfaces causes a shift from strongly to more weakly bound metal forms and (ii) atmospheric metal input is sorbed preferentially at the aggregate surfaces, and (iii) this input is weakly bound only. Lead is significantly enriched in the surface fractions compared with the cores, indicating ubiquitous input of Pb to the soils. The depletion of the mainly silicate-bound metals in the aggregate surface fractions compared with the core fractions correlates with the mean annual temperature and the mean annual precipitation, which both favor silicate weathering.

Among the controls on the fate of harzardous persistent organic pollutants (POPs) in the environment, soil organic matter (SOM) and climate play an outstanding role. Thus, it may be possible to predict POP concentrations at background sites from SOM properties and climatic elements. We therefore related polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) concentrations in 18 mollic epipedons under native grassland to SOM properties (lignin-derived phenols, polycarboxylic benzoic acids [PCBAs], aromaticity, and polarity of alkali-extractable SOM) and climatic elements. The sum of 20 PAH ([Sigma]220PAHs) concentrations ranged from 63 to 321 [micro]g [kg.sup.-1], and that of 14 PCB ([Sigma]14PCBs) concentrations ranged from 7.9 to 93 [micro]g [kg.sup.-1], except at one contaminated site (3136 [micro]g [kg.sup.-1]). On average, phenanthrene (PHEN, 38% of the [Sigma]20PAHs concentrations) and naphthalene (NAPH, 28%) were the most abundant PAHs, congeners 28 (22% of the [Sigma]14PCB concentrations) and 101 (17%) were the most abundant PCBs. Soil organic C (SOC) concentrations correlated with the [Sigma]20PAHs concentrations; the C concentration in the sum of eight PCBAs, a marker for black C, correlated with the concentrations of higher molecular weight PAHs, except in soils with cyric temperature regime. The [Sigma]14PCBs concentrations was independent of any soil property. The contribution of NAPH to the [Sigma]20PAHs concentrations and that of the up to tetrachlorinated PCBs to the [Sigma]14PCBs concentrations decreased with increasing mean annual temperature (MAT). The percentages of PCB 101 increased with increasing MAT. However, the temperature effect was not strong. Mean annual precipitation (MAP) neither effected PAH nor PCB patterns. Our results indicate that the easily measured SOC concentrations may be used to predict PAH concentrations in native grassland soils of the prairie. Including MAT improves the prediction of NAPH concentrations. The influence of MAT on PCB concentrations is obvious, but the correlation is too weak to be used for reliable predictions.

The climatic regime influences the turnover of P in soils, resulting in shifts in P fractions of different bonding forms. Here, we aimed at (i) identifying possible changes in P fractions as related to mean annual temperature (MAT) and mean annual precipitation (MAP), as well as (ii) elucidating how these patterns change under long-term agriculture. We analyzed different P fractions after sequential extraction according to the Hedley procedure from the top 10 cm of 18 native grassland sites and adjacent long-term agricultural fields along a temperature and precipitation transect from central Saskatoon to south Texas. The analyses were performed on bulk soils and clay fractions. The results showed that total P (Ptot) concentrations decreased with increasing MAT but were not clearly related to MAP. The contributions of total inorganic P (Pitot) and total organic P (Potot) to Ptot did neither change with MAT nor with MAP. The proportions of individual soil fractions were shifted from the labile and easily extractable P bonding forms to the more stable, residual P fractions with increasing annual temperature. Arable cropping induced loss of organic P (Po). The relationships to the climatic factors were sustained for the arable soil, but better reflected in the clay fractions than in the bulk soil. We conclude that there is a gross pattern of soil P distribution related to the climate, likely reflecting the increased biological processing as well as and progressing weathering and neoformation of secondary mineral phases as annual temperatures rise. [ABSTRACT FROM AUTHOR]