Studying organic matter molecular assemblage within a whole organic soil by nuclear magnetic resonance

This work shows the applicability of two-dimensional (2D) (1)H-(13)C heteronuclear correlation (HETCOR) nuclear magnetic resonance (NMR) spectroscopy to the characterization of whole soils. A combination of different mixing times and cross polarization (CP) methods, namely Lee-Goldberg (LG)-CP and Ramp-CP are shown to afford, for the first time, intra- and inter- molecular connectivities, allowing for molecular assemblage information to be obtained on a whole soil. Our results show that, for the brackish marsh histosol under study, two isolated domains could be detected. The first domain consists of O-alkyl and aromatic moieties (lignocellulose material), while the second domain is comprised of alkyl type moieties (cuticular material). The role of these domains is discussed in terms of hydrophobic organic compound sorption within soil organic matter (SOM), including the possible effects of wetting and drying cycles.     

Use of ecosystem information to improve soil organic carbon mapping of a Mediterranean island

Detailed maps of soil C are needed to guide sustainable soil uses and management decisions. The quality of soil C maps of Italian Mediterranean areas may be improved and the sampling density reduced using secondary data related to the nature of the ecosystem. The current study was conducted to determine: (i) the improvements obtainable in mapping soil C over a Mediterranean island by using ecosystem features and (ii) the effect of different sampling densities on the map accuracy. This work relied on field sampling (n=164) of soil properties measured over the island of Pianosa (Central Italy). Statistical analysis assessing the relationship between soil properties and ecosystem features revealed that the conceptual model of ecosystems defined on the basis of environmental features such as vegetation cover, land use, and soil type was mainly related to the variation of soil organic carbon (OC) content and to the type of Mediterranean environment. The distribution of ecosystems was used to improve the accuracy of soil OC maps obtainable by a simple interpolation approach (ordinary kriging). Substantial improvement was obtained by: (i) stratification into ecosystem types and (ii) applying locally calibrated regressions to satellite imagery that introduced both inter-ecosystem and intra-ecosystem information linked to vegetation features. This study showed that interpolation methods using information on ecosystem distribution can produce accurate maps of soil OC in Mediterranean environments, mostly because of the linkage between soil OC and vegetation types, which are spatially fragmented and heterogeneous.     

Stabilization of composted organic matter after application to a humus-free sandy mining soil

The use of mining substrates for recultivation purposes is limited due to their low organic matter (OM) contents. In a 1-yr laboratory experiment we evaluated the stabilization of biowaste compost added to a humus-free sandy mining soil to examine the suitability of compost amendment for the formation of stable soil organic matter (SOM). The stabilization process was characterized by measuring enrichment of OM and nitrogen in particle size fractions obtained after dispersion with different amounts of energy (ultrasonication and shaking in water), carbon mineralization, and amount of dissolved organic carbon (DOC). During the experiment, 17.1% of the organic carbon (OC) was mineralized. Organic carbon enrichment in the < 20-micron particle size fraction at the beginning of the experiment was in the range of natural soils with similar texture. Within 12 mo, a distinct OC redistribution from coarse into fine fractions was found with both dispersion methods. The accumulation of OC was more pronounced for the size separates obtained by ultrasonication, where the carbon distribution between 0.45- to 20-micron particle size fractions increased from 30% at the beginning to 71% at the end of the experiment. Dissolved organic carbon contents ranged between 50 and 68 g kg-1 OC and decreased during the incubation. In conclusion, the exponential decrease of carbon mineralization and the OC enrichment in the fine particle size fractions both indicated a distinct OM stabilization in the mining soil.     

Interactions of carbamazepine in soil: effects of dissolved organic matter

Pharmaceutical compounds (PCs) and dissolved organic matter (DOM) are co-introduced into soils by irrigation with reclaimed wastewater. We targeted carbamazepine (CBZ) as a model compound to study the tertiary interactions between relatively polar PCs, DOM, and soil. Sorption-desorption behavior of CBZ was studied with bulk clay soil and the corresponding clay size fraction in the following systems: (i) without DOM, (ii) co-introduced with DOM, and (iii) pre-adsorption of DOM before CBZ introduction. Sorption of the DOM to both sorbents was irreversible and exhibited pronounced sorption-desorption hysteresis. Carbamazepine exhibited higher sorption affinity and nonlinearity, and a higher degree of desorption hysteresis with the bulk soil than the corresponding clay size fraction. This was probably due to specific interactions with polar soil organic matter fractions that are more common in the bulk soil. Co-introduction of CBZ and DOM to the soil did not significantly affect the sorption behavior of CBZ; however, following pre-adsorption of DOM by the bulk soil, an increase in sorption affinity and decrease in sorption linearity were observed. In this latter treatment, desorption hysteresis of CBZ was significantly increased for both sorbents. We hypothesize that this was due to either strong chemical interactions of CBZ with the adsorbed DOM or physical encapsulation of CBZ in DOM-clay complexes. Based on this study, we suggest that DOM facilitates stronger interactions of polar PCs with the solid surface. This mechanism can reduce PC desorption ability in soils.     

Sorption of hydrophobic pesticides on a Mediterranean soil affected by wastewater, dissolved organic matter and salts

Irrigation with treated wastewaters as an alternative in countries with severe water shortage may influence the sorption of pesticides and their environmental effects, as wastewater contains higher concentrations of suspended and dissolved organic matter and inorganic compounds than freshwater. We have examined the sorption behaviour of three highly hydrophobic pesticides (the herbicide pendimethalin and the insecticides α-cypermethrin and deltamethrin) on a Mediterranean agricultural soil using the batch equilibration method. We considered wastewater, extracts from urban sewage sludge with different dissolved organic carbon contents, and inorganic salt solutions, using Milli Q water as a control. All pesticides were strongly retained by soil although some sorption occurred on the walls of the laboratory containers, especially when wastewater and inorganic salt solutions were used. The calculation of distribution constants by measuring pesticide concentrations in soil and solution indicated that pendimethalin sorption was not affected whereas α-cypermethrin and deltamethrin retention were significantly enhanced (ca. 5 and 2 times, respectively) when wastewater or salt solutions were employed. We therefore conclude that the increased sorption of the two pesticides caused by wastewater cannot be only the result of its dissolved organic carbon content, but also of the simultaneous presence of inorganic salts in the solution.     

Effect of dissolved organic matter from sludge and sludge compost on soil copper sorption

Interaction of Cu with dissolved organic matter (DOM) is an important physicochemical process affecting Cu mobility in soils. The aim of this study was to investigate the effects of DOM from anaerobically digested dewatered sludge and sludge compost on the sorption of Cu on an acidic sandy loam and a calcareous clay loam. In the presence of DOM, Cu sorption capacity decreased markedly for both soils, especially for the calcareous soil. The Cu sorption isotherms could be well described by the Freundlich equation (r2 = 0.99), and the binding intensity parameter of soils in the presence of sludge DOM was lower than compost DOM. An increase in DOM concentration significantly reduced the sorption of Cu by both soils. Within the Cu and DOM concentration range studied, the decrease in Cu sorption caused by sludge DOM was consistently greater than that of compost DOM. This might be attributed to the greater amount of hydrophobic fraction of DOM in the compost. Moreover, the reduction of Cu sorption caused by DOM was more obvious in the soil with higher pH. In addition, the sorption of Cu increased with an increase in pH for both soils without the addition of DOM, while Cu sorption in the presence of DOM was unexpectedly decreased with an increase in pH at a pH >6.8. This implied that DOM produced by sludge or other C-enriched organic wastes heavily applied on calcareous soils might facilitate the leaching loss of Cu because of the formation of soluble DOM-metal complexes.     

Sorptive and desorptive fractionation of dissolved organic matter by mineral soil matrices

Interactions of dissolved organic matter (DOM) with soil minerals, such as metal oxides and clays, involve various sorption mechanisms and may lead to sorptive fractionation of certain organic moieties. While sorption of DOM to soil minerals typically involves a degree of irreversibility, it is unclear which structural components of DOM correspond to the irreversibly bound fraction and which factors may be considered determinants. To assist in elucidating that, the current study aimed at investigating fractionation of DOM during sorption and desorption processes in soil. Batch DOM sorption and desorption experiments were conducted with organic matter poor, alkaline soils. Fourier-transform infrared (FTIR) and UV-Vis spectroscopy were used to analyze bulk DOM, sorbed DOM, and desorbed DOM fractions. Sorptive fractionation resulted mainly from the preferential uptake of aromatic, carboxylic, and phenolic moieties of DOM. Soil metal-oxide content positively affected DOM sorption and binding of some specific carboxylate and phenolate functional groups. Desorptive fractionation of DOM was expressed by the irreversible-binding nature of some carboxylic moieties, whereas other bound carboxylic moieties were readily desorbed. Inner-sphere, as opposed to outer-sphere, ligand-exchange complexation mechanisms may be responsible for these irreversible, as opposed to reversible, interactions, respectively. The interaction of aliphatic DOM constituents with soil, presumably through weak van der Waals forces, was minor and increased with increasing proportion of clay minerals in the soil. Revealing the nature of DOM-fractionation processes is of great importance to understanding carbon stabilization mechanisms in soils, as well as the overall fate of contaminants that might be associated with DOM.     

Paramagnetic effects on solid state carbon-13 nuclear magnetic resonance spectra of soil organic matter

The effects of paramagnetic species on solid state 13C nuclear magnetic resonance (NMR) spectra were quantified in a series of doping experiments. The degree of signal loss caused by paramagnetic metals was shown to depend not only on the quantity, but also on the nature of the paramagnetic species, as well as the intimacy of contact with the organic substrate and the type of NMR experiment. Two mechanisms of signal loss were distinguished--signal loss via loss of magnetic field homogeneity, which affects all 13C nuclei in a sample, and signal loss via interaction between electronic and nuclear spins, the effects of which were localized to the close environment of the paramagnetic species. Loss of field homogeneity is important for manganese species, but not for copper species, and is equally important for both cross polarization and Bloch decay experiments. The interaction between electronic and nuclear spins is highly dependent on the spin-lattice relaxation rate constant of the free electron (T1e), as cations with very short T1e values (e.g., Pr3+) cause less signal loss than cations with longer T1e values (e.g., Cu2+, Mn2+). Cross polarization spectra are shown to be more susceptible than Bloch decay spectra to this mechanism of signal loss. Signal loss and increased relaxation rates brought about by paramagnetic species can be used to provide information on soil organic matter (SOM) heterogeneity in the submicron range. This is demonstrated for SOM doped with paramagnetic cations where selective signal loss and increased relaxation rates are used to determine the nature of cation exchange sites.     

Relevance of organic matter fractions as predictors of wastewater sludge mineralization in soil

Seventeen different wastewater sludges were characterized using both chemical and organic matter fractionation methods (water extraction, Van Soest method, and acid hydrolysis) and 6-mo incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis (MFA) were then performed to establish relationships between composition and C and N mineralization of sludges. Carbon and N concentrations covered a wide range of values, but organic carbon (C(o)) to organic nitrogen (N(o)) ratios were relatively low (from 5 to 19). Carbon and N were mainly distributed in the most soluble fractions of the Van Soest method and in the water-insoluble fraction at 100 degrees C. Carbon mineralization varied from 180 to 661 g C kg(-1) organic C added during the 168-d incubation. The addition of sludges led to different inorganic N dynamics: from -3.3 to +120.0 g N kg(-1) sludge organic C mineralized after the 168-d incubation. Fractionation studies showed that the most discriminating method was acid hydrolysis. Carbon mineralization was linked with the proportion of sludge N and C present in the lignin-like fraction (r = -0.68 and -0.65, respectively). Significant relationships were established between N mineralization and N(o) to C(o) ratio (0.88 < r < 0.95) and the C(o) to N(o) ratio of sludges, the C to N ratio of the soluble fraction obtained by the Van Soest method, the water-soluble fraction at 100 degrees C, and the C and N present in the acid-hydrolyzable fraction. Finally, multiple factor analysis also enabled establishing a sludge typology using five clusters based on composition and mineralization characteristics.     

Virus retention and transport as influenced by different forms of soil organic matter

Organic materials are widespread in natural soil and aquatic environments. Their effect on virus transport is very important in assessing the risk for contamination of ground water by viruses. This study aimed to determine how different forms (mineral-associated and dissolved) of natural organic matter influence the retention and transport of two bacteriophages (MS-2 and phiX174) in two porous media (a sand and a soil). We found that mineral-associated organic matter significantly promoted the transport of one virus (MS-2) but not the other (phiX174) in a phosphate-buffered saline solution. Similarly, MS-2 was retained less in sand columns with increasing concentrations of dissolved humic acid, while little effect was observed for phiX174 under the same conditions. The two viruses have different surface properties and thus exhibited different reactivity to the metal oxides present on sand particles and were affected differently by organic matter. Because the organic matter used in the study was negatively charged and hydrophilic, blocking of virus sorption sites and increasing of virus-medium electrostatic repulsion arising from modification of the sand and virus surface by organic matter are probably responsible for the facilitated transport. For dissolved humic acid, its competition for sorption sites with viruses was an additional mechanism involved. This study suggests that the effect of organic matter varied depending on the organic material properties and the type of viruses involved. As a general trend, the effect of organic matter was dominated by electrostatic rather than hydrophobic interactions.     

Sorption and fractionation of dissolved organic matter and associated phosphorus in agricultural soil

Mobility of dissolved organic matter (DOM) strongly affects the export of nitrogen (N) and phosphorus (P) from soils to surface waters. To study the sorption and mobility of dissolved organic C and P (DOC, DOP) in soil, the pH-dependent sorption of DOM to samples from Ap, EB, and Bt horizons from a Danish agricultural Humic Hapludult was investigated and a kinetic model applicable in field-scale models tested. Sorption experiments of 1 to 72 h duration were conducted at two pH levels (pH 5.0 and 7.0) and six initial DOC concentrations (0-4.7 mmol L(-1)). Most sorption/desorption occurred during the first few hours. Dissolved organic carbon and DOP sorption decreased strongly with increased pH and desorption dominated at pH 7, especially for DOC. Due to fractionation during DOM sorption/desorption at DOC concentrations up to 2 mmol L(-1), the solution fraction of DOM was enriched in P indicating preferred leaching of DOP. The kinetics of sorption was expressed as a function of how far the solution DOC or DOP concentrations deviate from "equilibrium." The model was able to simulate the kinetics of DOC and DOP sorption/desorption at all concentrations investigated and at both pH levels making it useful for incorporation in field-scale models for quantifying DOC and DOP dynamics.     

Long-term effect of a single application of organic refuse on carbon sequestration and soil physical properties

Restoration of degraded lands could be a way to reverse soil degradation and desertification in semiarid areas and mitigate greenhouse gases (GHG). Our objective was to evaluate the long-term effects of a single addition of organic refuse on soil physical properties and measure its carbon sequestration potential. In 1988, a set of five plots (87 m(2) each) was established in an open desert-like scrubland (2-4% cover) in Murcia, Spain, to which urban solid refuse (USR) was added in a single treatment at different rates. Soil properties were monitored over a 5-yr period. Sixteen years after the addition, three of the plots were monitored again (P0: control, P1: 13 kg m(-2), P2: 26 kg m(-2) of USR added) to assess the lasting effect of the organic addition on the soil organic carbon (SOC) pools and on the physical characteristics of the soil. The SOC content was higher in P2 (16.4 g kg(-1)) and in P1 (11.8 g kg(-1)) than in P0 (7.9 g kg(-1)). Likewise, aerial biomass increased from 0.18 kg m(-2) in P0 up to 0.27 kg m(-2) in P1 and 0.46 kg m(-2) in P2. This represents a total C sequestration of 9.5 Mg ha(-1) in P2 and 3.4 Mg ha(-1) in P1, most of the sequestered C remaining in the recalcitrant soil pool. Additionally, higher saturated hydraulic conductivity, aggregate stability, and available water content values and lower bulk density values were measured in the restored plots. Clearly, a single addition of organic refuse to the degraded soils to increase the potential for C sequestration was effective.     

Biowaste effects on soil and native plants in a semiarid ecosystem

Many soils of the Mediterranean region with a semiarid climate are subjected to progressive degradation as a result of water erosion. Biosolids and municipal solid wastes (MSW) were surface-applied once at three rates (40, 80, and 120 Mg ha(-1)) to different plots in a degraded semiarid ecosystem. The study was conducted to determine the effects of such applications on soil chemical properties and native vegetation over a three-year period. Soil N, P, and K initially increased with increasing biowaste application rates, but then decreased over time. Levels of Zn and Cu were higher in MSW than biosolid-treated plots, and increased in both years after application. Concentrations of soil Cd, Pb, Ni, and Cr did not change as a result of biowaste amendment in the study period. The growth of native plants was enhanced by the addition of biowastes. Total plant canopy and plant biomass increased significantly and remained higher in all treatments than in the control plot over the three-year period. The species richness of native plants decreased with increasing biowaste rates. Differences in the development of native plant communities between treatments were observed, and were more remarkable three years after biowaste application. Tissue N, P, K, Zn, and Cu levels increased with the biowaste application rate, but concentrations of tissue Pb, Cd, Ni, and Cr did not increase significantly. Biowastes applied at the rate of 80 Mg ha(-1) gave rise to the most favorable soil and native vegetation results while avoiding environmental risks.     

Remediation of heavy metal-contaminated forest soil using recycled organic matter and native woody plants

The main aim of this study was to determine how the application of a mulch cover (a mixture of household biocompost and woodchips) onto heavy metal-polluted forest soil affects (i) long-term survival and growth of planted dwarf shrubs and tree seedlings and (ii) natural revegetation. Native woody plants (Pinus sylvestris, Betula pubescens, Empetrum nigrum, and Arctostaphylos uva-ursi) were planted in mulch pockets on mulch-covered and uncovered plots in summer 1996 in a highly polluted Scots pine stand in southwest Finland. Spreading a mulch layer on the soil surface was essential for the recolonization of natural vegetation and increased dwarf shrub survival, partly through protection against drought. Despite initial mortality, transplant establishment was relatively successful during the following 10 yr. Tree species had higher survival rates, but the dwarf shrubs covered a larger area of the soil surface during the experiment. Especially E. nigrum and P. sylvestris proved to be suitable for revegetating heavy metal-polluted and degraded forests. Natural recolonization of pioneer species (e.g., Epilobium angustifolium, Taraxacum coll., and grasses) and tree seedlings (P. sylvestris, Betula sp., and Salix sp.) was strongly enhanced on the mulched plots, whereas there was no natural vegetation on the untreated plots. These results indicate that a heavy metal-polluted site can be ecologically remediated without having to remove the soil. Household compost and woodchips are low-cost mulching materials that are suitable for restoring heavy metal-polluted soil.     

Combined effect of natural organic matter and surfactants on the apparent solubility of polycyclic aromatic hydrocarbons

Both natural organic matter (NOM) and surfactants are known to enhance the apparent aqueous solubility of hydrophobic organic contaminants (HOCs) in aqueous systems. In this study, the combined effect of NOM and surfactants on enhancing the solubility of HOCs was investigated, since both may occur and affect the fate and transport of HOCs in natural aqueous environments. Experimental results indicated that the apparent solubility of naphthalene, phenanthrene, and pyrene in NOM and anionic surfactant solution was lower than their solubility in NOM solution alone. However, the apparent solubility of an HOC in NOM and nonionic surfactant solution is almost the same as the sum of the HOC's solubility in NOM solution plus its solubility in nonionic surfactant solution. The observation that apparent aqueous solubility of HOCs in NOM and anionic surfactant solution is decreased is probably due to the fact that the cations that are released when the anionic surfactant dissociates may form ion pairs with acidic or phenolic groups associated with the NOM. This serves to increase the size of hydration of these groups, thereby decreasing the effective size of the nonpolar moieties associated with the NOM, and thus decreasing hydrophobic partitioning of the HOCs into the NOM. The results presented here will help us to understand the effect of NOM and surfactants on the fate and transport of HOCs in aquatic systems.     

Sorption and desorption of naphthalene by soil organic matter: importance of aromatic and aliphatic components

Nonlinear isotherm behavior has been reported for the sorption of hydrophobic organic compounds (HOCs) in soil organic matter (SOM), but the exact mechanisms are unknown. Our objective was to provide insight into the sorption mechanism of HOCs in SOM by studying the sorption-desorption processes of naphthalene in a mineral soil, its humic fractions, and lignin. Additionally, humin and lignin were used for studying the effects of temperature and cosolvent on HOC sorption. All isotherms were nonlinear. The humin and lignin isotherms became more linear at elevated temperatures and with the addition of methanol indicating a condensed to expanded structural phase transition. Isotherm nonlinearity and hysteresis increased in the following order: soil humic acid (HA) < soil < soil humin. Of the samples, aliphatic-rich humin exhibited the largest degree of nonlinearity and had the highest sorption capacity for naphthalene. High nonlinearity and hysteresis in humin were most likely caused by its condensed structure. A novel aliphatic, amorphous condensed conformation is proposed. This conformation can account for both high sorption capacities and increased nonlinearity observed for aliphatic-rich samples and can explain many sorption disparities discussed in the literature. This study clearly illustrates the importance of both aliphatic and aromatic moieties for HOC sorption in SOM.     

Spectroscopic and wet chemical characterization of solid waste organic matter of different age in landfill sites, southern Germany

Landfill sites are potential sources of hazardous emissions by degradation and transformation processes of waste organic matter. Its chemical composition and microbial degradability are key factors for risk management, after-care, and estimation of potential emissions. The aim of the study is to provide information about composition and extent of transformation of waste organic matter in four landfill sites in Bavaria, Southern Germany by means of (13)C NMR spectroscopy, acid-hydrolyzable carbohydrates, chloroform-methanol extractable lipids, acid-hydrolyzable proteins, and lignin compounds after CuO oxidation. Ten samples of about 20 to 25 yr, 15 to 20 yr, and 5 to 10 yr of deposition each were taken at 2 m depth intervals by grab drilling till 10-m depth. Increasing temperatures from about 15 degrees C at 2-m depth to >40 degrees C at 10-m depth are found at some of the sites, representing optimum conditions for mesophile methane bacteria. Moisture contents of 160 to 310 g kg(-1) (oven dry), however, provide limiting conditions for anaerobic biodecay. Spectroscopic and chemical variables generally indicate a low extent of biodegradation and transformation at all sites despite a considerable heterogeneity of the samples. Independent of the time and depth of deposition more than 50% of the carbohydrate fraction of the waste organic matter provide a high potential for methane emissions and on-site energy production. There was no significant accumulation of long-chain organic and aromatic compounds, and of lignin degradation products even after more than 25 yr of rotting indicating higher extent of decomposition or stabilization of the waste organic matter. Installation of seepage water cleaning and recirculation systems are recommended to increase suboptimal moisture contents with respect to microbial methanogenesis, energy production, and long-term stabilization of municipal solid waste.     

Prediction of soil organic partition coefficients by a soil leaching column chromatographic method

The soil organic partition coefficient (Koc) is one of the most important parameters to depict the transfer and fate of a chemical in the soil-water system. Predicting Koc by using a chromatographic technique has been developing into a convenient and low-cost method. In this paper, a soil leaching column chromatograpy (SLCC) method employing the soil column packed with reference soil GSE 17201 (obtained from Bayer Landwirtschaftszentrum, Monheim, Germany) and methanol-water eluents was developed to predict the Koc of hydrophobic organic chemicals (HOCs), over a log Koc range of 4.8 orders of magnitude, from their capacity factors. The capacity factor with water as an eluent (k'w) could be obtained by linearly extrapolating capacity factors in methanol-water eluents (k'w) with various volume fractions of methanol (symbol in text). The important effects of solute activity coefficients in water on k'w and Koc were illustrated. Hence, the correlation between log Koc and log k'w (and log k') exists in the soil. The correlation coefficient (r) of the log Koc vs. log k'w correlation for 58 apolar and polar compounds could reach 0.987, while the correlation coefficients of the log Koc -log k' correlations were no less than 0.968, with (symbol in text)ranging from 0 to 0.50. The smaller the (symbol in text), the higher the r. Therefore, it is recommended that the eluent of smaller (symbol in text), such as water, be used for accurately estimating Koc. Correspondingly, the r value of the log Koc -log k'w correlation on a reversed-phase Hypersil ODS (Thermo Hypersil, Kleinostheim, Germany) column was less than 0.940 for the same solutes. The SLCC method could provide a more reliable route to predict Koc indirectly from a correlation with k'w than the reversed-phase liquid chromatographic (RPLC) one.     

A new way to use solid-state carbon-13 nuclear magnetic resonance spectroscopy to study the sorption of organic compounds to soil organic matter

Several solid-state 13C nuclear magnetic resonance (NMR) techniques were used to characterize soil organic matter spiked with 13C-labeled organic compounds spanning a range of hydrophobicities (benzoic acid, benzophenone, naphthalene, phenanthrene, and palmitic acid). The chemical shifts of NMR resonances of the sorbed species were shifted by up to 3 ppm relative to those of the neat compounds. Sorption also resulted in increased resonance linewidth for the compounds containing a single 13C label, indicating the presence of a range of different chemical environments at the sites of sorption. On the other hand, sorption decreased the linewidth of the resonance of naphthalene, which was uniformly 13C-labeled. This was attributed to the removal of intermolecular 13C-13C dipolar coupling. Heterogeneity of the organic matter was demonstrated using the spectral editing technique proton spin relaxation editing (PSRE), which enabled the identification and quantification of charcoal-rich domains characterized by rapid rates of proton spin-lattice relaxation in the static frame (T1H), and humic domains characterized by slow rates of T1H relaxation. Furthermore it was demonstrated that the sorbed 13C-labeled molecules "inherit" the T1H "signature" of the organic matrix in their immediate vicinity. Thus PSRE on the spiked soils enabled evaluation of the relative affinity of the two domain types for the sorbate molecules. The charcoal-rich domains were shown to have a twofold to tenfold greater affinity for the organic compounds, with greater differences found for the more hydrophobic compounds.     

Ion cycling in hemlock-northern hardwood forests of the southern Lake Superior region: a preliminary study

Upland forests of the southern Lake Superior region are diverse and contain a shifting mosaic of eastern hemlock [Tsuga canadensis (L.) Carr.] and northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.). In this study, we survey the relative effects of management practice (old growth vs. managed), forest cover type (hemlock vs. northern hardwood), and soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod) on ion cycling as a precursor to a longer-term, more detailed study. Bulk precipitation, throughfall, and soil leachates at three depths were collected for two growing seasons in eight stands on the Ottawa National Forest in the Upper Peninsula of Michigan. A total of 1210 solutions were analyzed for pH, Na, K, Mg, Ca, Cl, NO3, and SO4. Losses of base cations (Ca, Mg, K) and SO4 from the bottom of the rooting zone generally were greater in old-growth than in managed northern hardwoods on both fragic and nonfragic soils. Leaching losses of base cations and NO3 usually were greater beneath old-growth northern hardwoods than beneath old-growth hemlock on both soil types and for both forest cover types and management practices on fragic than nonfragic soils. Management practice, forest cover type, and soil type all appear to affect ion cycling within these forests. All of the stands featured striking losses of base cations that probably are influenced strongly by NO3 and SO4 in atmospheric deposition.