Ludwig Haumaier

Black carbon in density fractions of anthropogenic soils of the Brazilian Amazon region.

Abstract Frequent charcoal findings together with black carbon concentrations in the soil organic matter (SOM) of up to 35% provided evidence that black carbon is important for the SOM stability in Terra Preta soils. This paper aims to investigate whether black carbon is additionally stabilised by organo-mineral complexation. For this purpose black carbon was analysed in density fractions using benzenecarboxylic acids as molecular markers. Density fractions were also studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Concentrations and total amounts of black carbon were generally highest in the light fraction indicating that a major part of black carbon is not chemically stabilised but intrinsically refractory. On the other hand, a large part of black carbon was also found in the heavier fractions, where it was partly embedded within plaques of iron and aluminium oxides on mineral surfaces. The major part of black carbon in the medium fraction seemed to be organo-mineral complexed because we found amounts of black carbon in this fraction by wet chemical analysis but not by scanning electron microscopy and energy dispersive X-ray spectroscopy. The spectroscopic analysis can only detect particulate black carbon. Black carbon was particularly enriched in 30–40 cm soil depth, and in all fractions of Terra Preta soils compared to adjacent Oxisols. The occurrence of particulate black carbon together with potsherds in the subsoil horizons of Terra Preta soils indicate that this might be due to turbation processes or the soils were covered by earthworm or termite activities. Further research, however, is needed to clarify the transport mechanisms of black carbon into deeper soil horizons.

Changes in properties of soil-derived dissolved organic matter induced by biodegradation

Properties of dissolved organic matter (DOM) determine its biodegradation. In turn, biodegradation changes the properties of the remaining DOM, which may be decisive for the formation of stable organic carbon in soil. To gain information on both mechanisms and controlling factors of DOM biodegradation and the properties of biodegraded DOM, we investigated changes in the composition of 13 different DOM samples extracted from maize straw, forest floors, peats, and agricultural soils during a 90-day incubation using UV absorbance, fluorescence emission spectroscopy, FTIR-spectroscopy, 1 H-NMR spectroscopy, pyrolysis-field ionization mass spectroscopy (Py-FIMS), and 13 C natural abundance before and after incubation. Changes in the DOM properties were related to the extent of biodegradation determined by the release of CO2. Increasing UV absorption and humification indices deduced from fluorescence emission spectra, and increasing portions of aromatic H indicated relative enrichment of aromatic compounds during biodegradation. This enrichment significantly correlated with the amount of DOC mineralized suggesting that aromatic compounds were relatively stable and slowly mineralized. 13 C depletion during the incubation of highly degradable DOM solutions indicated an enrichment of lignin-derived aromatic compounds. Py-FI mass spectra indicated increasing contents of phenols and lignin monomers at the expense of lignin dimers and alkylaromatics during incubation. This partial degradation of higher-molecular, lignin-derived DOM compounds was accompanied by relative increases in the proportions of lower-molecular degradation products and microbial metabolites. Carbohydrates, especially when abundant at high initial contents, seem to be the preferred substrate for microorganisms. However, four independent methods suggested also some microbial production of carbohydrates and peptides during DOM degradation. After incubation, the composition of highly degradable DOM samples became similar to relatively stable DOM samples with respect to aromaticity, carbohydrate content, and thermal stability. We conclude that DOM biodegradation seems to result in organic matter properties being a precondition for the formation of stable carbon. These structural changes induced by DOM biodegradation should also result in stronger DOM sorption to the soil matrix additionally affecting DOM stabilization. q 2003 Elsevier Science Ltd. All rights reserved.

Seasonal variations in the chemical composition of dissolved organic matter in organic forest floor layer leachates of old-growth Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) stands in northeastern Bavaria, Germany

Organic matter dissolved in thepercolation water of forest soils contributeslargely to element cycling and transport ofnatural and anthropogenic compounds. The wayand extent to which these processes areaffected depends on the amount and the chemicalcomposition of soluble organic matter. Becausethe amount of soluble organic matter variesseasonally with changes in the microbialactivity in soil, it seems reasonable to assumethat there may be also seasonal changes in thechemical composition of dissolved organicmatter. We examined dissolved organic matter inthe seepage waters of organic forest floorlayers over a 27-month period (1997–1999) intwo forest ecosystems, a 160-year-old Scotspine (Pinus sylvestris L.) stand and a90-year-old European beech (Fagussylvatica L.) forest. The forest floorleachates were analysed for bulk dissolvedorganic C, C in hydrophilic and hydrophobicdissolved organic matter fractions,lignin-derived phenols (CuO oxidation),hydrolysable neutral carbohydrates and uronicacids, hydrolysable amino sugars, and stablecarbon isotope composition. In addition, westudied the samples by use of liquid-state13C-nuclear magnetic resonance (NMR)spectroscopy.For both investigated forest sites we foundthat the dissolved organic carbonconcentrations in forest floor leachates werelargest during summer. They peaked after rainstorms following short dry periods (106–145 mgdissolved organic C l−1). The proportionsof C in the hydrophilic fractions were largestin winter and spring whereas in summer andautumn more C was found in the hydrophobicfraction. According to liquid-state 13C-NMR spectroscopy, summer and autumn samples hadlarger abundances of aromatic and aliphaticstructures as well as larger proportions ofcarboxyl groups whereas the winter and springsamples were dominated by resonances indicatingcarbohydrates. Wet-chemical analyses confirmedthese results. Winter and spring samples wererich in neutral carbohydrates and amino sugars.The summer and autumn samples contained morelignin-derived phenols which were also strongeroxidised than those in the winter and springsamples. Seasonal changes of δ13C valueswere found to reflect the changes in thechemical composition of dissolved organicmatter. Most negative values occurred whenisotopically light lignin-derived compoundswere abundant and less negative values whencarbohydrates predominated.The different vegetation, age of thestands, and underlying mineral soils resultedin different concentrations of dissolvedorganic carbon and in differences in thedistribution between hydrophobic andhydrophilic organic carbon. Despite of this,the results suggest that the trends in temporalvariations in the composition of dissolvedorganic matter in forest floor seepage waterwere remarkably similar for both sites.Dissolved organic matter in winter and springseems to be mainly controlled by leaching offresh disrupted biomass debris with a largecontribution of bacterial and fungal-derivedcarbohydrates and amino sugars. Dissolvedorganic matter leached from the forest floor insummer and autumn is controlled by thedecomposition processes in the forest floorresulting in the production of stronglyoxidised, water-soluble aromatic and aliphaticcompounds. The chemical composition ofdissolved organic matter in forest floorseepage water in winter and spring indicateslarger mobility, larger biodegradability, andless interaction with metals and organicpollutants than that released during summer andautumn. Thus, the impact of dissolved organicmatter on transport processes may varythroughout the year due to changes in itscomposition.

Black carbon—possible source of highly aromatic components of soil humic acids

Abstract Structural features and chemical composition of highly aromatic soil humic acids strongly suggest that these humic acids are derived from black carbon (charred plant residues, soot) and not from native plant materials. Humic acids from laboratory-oxidized black carbon show remarkable similarities to highly aromatic soil humic acids in their spectroscopic properties and chemical composition. Thus, black carbon is considered to be a possible source of the chemically most stable, aromatic soil carbon pool.

The composition of dissolved organic matter in forest soil solutions : changes induced by seasons and passage through the mineral soil

Dissolved organic matter in forest soils is a mixture of specific low-molecular-weight compounds and high-molecular-weight polyelectrolytes. The distribution of molecules of different molecular charge, weight, and size controls the reactivity of dissolved organic matter in the soil and, once exported from the soil, in the aqueous environment. The objective of this study was to track changes in the molecular composition of dissolved organic matter in soil as induced by seasons and the passage through the soil. In a 27-month field experiment, we collected seepage water from the organic forest floor layers and porewater in the mineral subsoil under a Scots pine (Pinus sylvestris L.) and a European beech (Fagus sylvatica L.) stand. In the solutions, we measured the concentrations of organic carbon (C) and the composition of organic matter in combined 3-month samples using liquid-state 1H-NMR spectroscopy. Parallel to seasonal variations in the concentration of dissolved organic C, the 1H-NMR spectra of dissolved organic matter in forest floor leachates showed remarkable changes. At the pine site, dissolved organic matter released during winter and spring contained larger proportions of H associated with O-containing structures and of low-molecular-weight compounds. During summer and autumn, the contribution of O-containing structures and low-molecular-weight compounds declined and broad signals in the aromatic and aliphatic region indicated the release of high-molecular-weight aromatic and aliphatic macromolecules. Forest floor leachates under beech showed a similar trend but a larger number of low-molecular-weight compounds was present in winter and spring samples. In spring, summer, and autumn samples acetate and sometimes succinate were most prominent. During the passage of dissolved organic matter through the upper mineral soil at the pine site, the number and intensity of signals due to low-molecular-weight compounds increased. These substances were thus more mobile than the macromolecules and/or released due to microbial transformation of organic matter. At the beech site subsoil porewater contained less low-molecular-weight compounds than the forest floor solutions but the present ones had increased signal intensities. We suggest that the differences of dissolved organic matter transformations during the passage through the upper mineral soil at the two sites were due to different microbial activity in the soils.

Sequential extractions and 31P-NMR spectroscopy of phosphorus forms in animal manures, whole soils and particle-size separates from a densely populated livestock area in northwest Germany

Abstract The solubility and forms of phosphorus (P) were investigated in manures from chicken and pigs, eight whole soil samples and clay-, silt-, and sand-size separates from an arable and a grassland soil. Total P (Pt) in liquid pig manure (16.2 g kg–1) and dry chicken manure (26.2 g kg–1) was distributed between residual P (39–41% Pt), H2SO4–P (17–27% Pt), labile resin- and NaHCO3–P (24–39% Pt), and NaOH-P (3–10% Pt). Most soils had larger proportions of NaOH-P and residual P, indicating reactions of manure-derived P compounds with pedogenic oxides and humic substances. Clay-size separates had the highest P-concentrations in all fractions and were particularly enriched in exchangeable and labile P forms. Solution 31P-nuclear magnetic resonance (NMR) spectra of 0.5 M NaOH extracts from manures and some soil samples showed greater signal intensities for orthophosphate and monoester P than 0.1 M NaOH extracts. This can be explained by alkaline hydrolysis phosphate diesters at higher NaOH concentrations and/or by preferential extraction of diesters at lower concentrations. The 31P-NMR spectra showed differences between the two manures and confirmed that increasing proportions of ester-P can be expected if they are spread to soils. The NaOH extracts of soil samples were characterized by large proportions of orthophosphate-P (mean 77% of assigned P compounds), which seemed to be slightly enriched in clay fractions whereas the extracts from silt contained more ester-P. Sequential extractions and 31P-NMR spectroscopy both showed that these excessively manured soils are likely to lose large amounts of P.

Humic substances distribution and transformation in forest soils

The distribution and transformation of humic substances in forest soils is investigated by CPMAS 13C NMR spectroscopy and chemical analyses. Studies on bulk soil samples and humic acid fractions indicate that different forest humus types result from different rates but similar pathways of litter decomposition. The main features of humification in the investigated forest humus profiles are preferential mineralization of carbohydrates, strong alteration of lignin leading to increasing proportions of carbon-substituted aromatic rings and loss of phenolic groups, increase in carboxyl group contents and accumulation of refractory alkyl components. The action of earthworms promotes transformation of plant residues to humic substances and incorporation of organic matter into stable organo-mineral complexes.

Organic Matter Dynamics in Forest Soils of Temperate and Tropical Ecosystems

Publisher Summary This chapter studies the organic matter dynamics in the forest soils of temperate and tropical ecosystems by detailed morphological observations, including micromorphology, and a combination of spectroscopic and chemical degradation methods. It discusses the primary resources like plant debris that are related to the parent materials of humification. Research is conducted to elucidate the role of secondary resources like microbial and animal residues, and of black carbon as a possible source of humic materials. The pathways of humification differ according to the chemical composition of the resources. Microbial resynthesis is important for proteins and carbohydrates, but protection of polysaccharides by recalcitrant molecules may occur. Mineralization of carbohydrates is responsible for the decline of O-alkyl C from the soil surface down to the deepest forest soil A subhorizon. Within the forest soil profiles, lignin is altered by side-chain oxidation, demethoxylation, and loss of phenolic structures. The evident increase of aryl C in humus-rich mineral soils is the result of a relative accumulation of the stable nonlignin structures. The chapter also discusses the dynamics of alkyl-C compounds.

Differences in the chemical composition of dissolved organic matter from waste material of different sources

Abstract. The chemical composition of waste-material-derived dissolved organic matter (DOM) was characterized by chemolytic analyses and 1H, 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. Dissolved organic matter was extracted by water from an aerobic fermented urban waste compost, a sewage sludge and a pig slurry and then fractionated using the XAD-8 method. The amount of water-extractable dissolved organic carbon (DOC) ranged from 3% in the sewage sludge to 22% in the pig slurry. Dissolved organic matter isolated from pig slurry was equally distributed between hydrophilic and hydrophobic DOC, whereas in the sewage-sludge-derived material the hydrophobic fraction was predominant. Dissolved organic C from the urban waste compost was mainly within the hydrophilic fraction. Wet-chemical analysis and 1H- and 13C-NMR spectra showed that both DOM fractions from the urban waste compost were low in neutral, acidic and amino sugars as well as in lignin-derived compounds. In turn, the materials were rich in low-molecular-weight aliphatic compounds. The chemical structure of both fractions is probably the result of the intensive transformation of urban waste compost during its fermentation. The hydrophilic fractions of DOM from sewage sludge and pig slurry contained considerable amounts of carbohydrates but were also rich in low-molecular-weight aliphatics. The respective hydrophobic fractions had the largest contents of CuO-extractable phenols which may in part derive from sources other than lignin. By contrast with the other materials, the hydrophobic fraction from the pig slurry seemed to contain polymeric rather than low-molecular-weight material. The 31P-NMR spectrum of the hydrophilic DOM fraction from urban waste compost did not show signals of inorganic or organic P compounds while the spectrum of the hydrophobic fraction revealed traces of monoester P, diester P, and orthophosphate. 31P-NMR spectroscopy suggested that both the hydrophobic and hydrophilic fractions from pig slurry did not contain organic P. The hydrophilic DOM fraction from sewage sludge contained orthophosphate, organic monoester P and a little pyrophosphate. The hydrophobic fraction contained mainly organic diester P and smaller amounts of teichoic acids and organic monoester P. Considering that water-soluble fractions of urban waste compost contained no easily plant-available P and a low content of labile organics, we conclude that this material contains less labile nutrients and is more refractory than the soluble constituents of pig slurry and sewage sludge.

Black carbon in grassland ecosystems of the world.

[1] Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific δ 13 C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14 C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13 C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m -2 ) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.