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Binding to minerals is one mechanism crucial toward the accumulation and stabilization of organic matter (OM) in soils. Of the various biochemicals produced by plants, lignin-derived phenols are among the most surface-reactive compounds. However, it is not known to what extent mineral-bound lignin-derived phenols can be analytically assessed by alkaline CuO oxidation. We tested the potential irreversible binding of lignin from three litters (blue oak, foothill pine, annual grasses) to five minerals (ferrihydrite, goethite, kaolinite, illite, montmorillonite) using the CuO-oxidation technique, along with bulk organic carbon (OC) sorption. Up to 56% of sorbed lignin could not be extracted from the minerals with the CuO-oxidation technique. The composition of the irreversibly bound lignin component differed markedly between minerals and from that of the parent litter leachates, indicating different bonding strengths related to individual monomers and conformations. The difference in extractability of individual phenols suggests that abiotic processes, such as sorption/desorption, should be taken into account when using CuO oxidation data for assessing lignin turnover in mineral matrixes. However, given the apparent relationship between aromaticity as indicated by carbon-specific UV absorbance (SUVA) and bulk OC sorption, it is likely that irreversible sorption is a concern for any technique that addresses the broad class of aromatic/phenolic compounds in soils and sediments.

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Insight in the molecular structure of humic acid (HA) and fulvic acid (FA) can contribute to identify relationships between their molecular properties, and further our quantitative abilities to model important organic matter functions such as metal complexation and association with mineral surfaces. Pyrolysis gas chromatography/mass spectrometry (Py-GC-MS) is used to compare the molecular composition of HA and FA. A systematic comparison was obtained by using samples from different environmental sources, including solid and aqueous samples from both natural and waste sources. The chemical signature of the pyrolysates was highly variable and no significant difference between HA and FA was found for major chemical groups, that is, carbohydrates, phenols, benzenes, and lignin phenols, together accounting for 62-96% of all quantified pyrolysis products. However, factor analysis showed that within each sample, FAs consistently differed from corresponding HAs in a larger contribution from mono- and polyaromatic hydrocarbons and heterocyclic hydrocarbons, together accounting for 3.9-44.5% of the quantified pyrolysis products. This consistent difference between FAs and corresponding HAs, suggests that their binding properties may, in addition to the carboxyl and phenolic groups, be influenced by the molecular architecture. Py-GC-MS may thus contribute to identify relationships between HA and FA binding- and molecular-properties.

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The novel HTC system coupled to an isotope ratio mass spectrometer resulted in significantly improved sensitivity. The system is suitable for salt-containing liquids and compounds that are resistant to oxidation, and it offers a large concentration range. A second paper (which follows this one in this issue) will present a more comprehensive assessment of the analytical performance with a broad set of solutions and real samples. This highly efficient TOC stable isotopic analyzer will probably open up new possibilities in biogeochemical carbon cycle research.

Background and aims Quarrying causes severe degradation of soils and forest cover that can be recovered partially when the quarries are abandoned and re-colonised by plants. To understand the recovery of soil functionality and nutrient cycling, we studied the development of soil phosphorus pools during Scots pine (Pinus sylvestris) revegetation in a disused sand quarry in Northwestern Russia. Methods Sites that had been developing for different times since abandonment were compared to the parent sand and an adjacent undisturbed forest. Phosphorus speciation in genetic horizons of soil profiles was determined by sequential fractionation and solution phosphorus-31 nuclear magnetic resonance spectroscopy. Results Rapid transformations in soil properties occurred in 40 years, with a marked decline in pH and an accumulation of organic matter. Phosphorus transformations were shaped by geochemical processes, with a rapid release of inorganic phosphorus from primary minerals and accumulation of organic phosphorus to concentrations exceeding those found in the undisturbed site. Adsorbed and/or precipitated phosphorus increased rapidly, despite few reactive mineral colloidal surfaces. Conclusions Natural succession of Scots pine in post-mining landscapes promotes ecosystem restoration through the rapid re-establishment of the biogeochemical cycles of organic matter and phosphorus. This study also provides an important example of biogeochemical phosphorus cycling during the initial stages of pedogenesis.