Showing papers by "Karsten Kalbitz published in 2014"

Soil aggregation and the stabilization of organic carbon as affected by erosion and deposition

Abstract: The importance of soil aggregation in determining the dynamics of soil organic carbon (SOC) during erosion, transportation and deposition is poorly understood. Particularly, we do not know how aggregation contributes to the often-observed accumulation of SOC at depositional sites. Our objective was to assess how aggregation affects SOC stabilization in comparison to interactions of SOC with minerals. We determined and compared aggregate size distributions, SOC distribution in density fractions, and lignin-derived phenols from aggregated soil samples at both eroding and depositional sites. The stabilization effect of aggregation was quantified by comparing mineralization from intact and crushed macro-aggregates. Deposition of eroded soil material resulted in carbon (C) enrichment throughout the soil profile. Both macro-aggregate associated SOC and C associated with minerals (heavy fraction) increased in their importance from the eroding to the depositional site. In the uppermost topsoil (0–5 cm), SOC mineralization from intact aggregates was larger at the depositional site than at the eroding site, reflecting the large input of labile organic matter (plant residues) promoting aggregation. Contrastingly, in the subsoil, mineralization rates were lower at the depositional site because of effective stabilization by interactions with soil minerals. Aggregate crushing increased SOC mineralization by 10–80% at the eroding site, but not at the depositional site. The content of lignin-derived phenols did not differ between eroding and depositional sites in the topsoil (24.6–30.9 mg per g C) but was larger in the subsoil of the eroding site, which was accompanied by higher lignin oxidation. Lignin data indicated minor effects of soil erosion and deposition on the composition of SOC. We conclude that SOC is better protected in aggregates at the eroding than at the depositional site. During transport disaggregation and consequently SOC mineralization took place, while at the depositional site re-aggregation occurred mainly in the form of macro-aggregates. However, this macro-aggregation did not result in a direct stabilization of SOC. We propose that the occlusion of C inside aggregates serves as a pathway for the eroded C to be later stabilized by organo-mineral interaction.

Soil Organic Carbon Redistribution by Water Erosion – The Role of CO2 Emissions for the Carbon Budget

Abstract: A better process understanding of how water erosion influences the redistribution of soil organic carbon (SOC) is sorely needed to unravel the role of soil erosion for the carbon (C) budget from local to global scales. The main objective of this study was to determine SOC redistribution and the complete C budget of a loess soil affected by water erosion. We measured fluxes of SOC, dissolved organic C (DOC) and CO2 in a pseudo-replicated rainfall-simulation experiment. We characterized different C fractions in soils and redistributed sediments using density fractionation and determined C enrichment ratios (CER) in the transported sediments. Erosion, transport and subsequent deposition resulted in significantly higher CER of the sediments exported ranging between 1.3 and 4.0. In the exported sediments, C contents (mg per g soil) of particulate organic C (POC, C not bound to soil minerals) and mineral-associated organic C (MOC) were both significantly higher than those of non-eroded soils indicating that water erosion resulted in losses of C-enriched material both in forms of POC and MOC. The averaged SOC fluxes as particles (4.7 g C m−2 yr−1) were 18 times larger than DOC fluxes. Cumulative emission of soil CO2 slightly decreased at the erosion zone while increased by 56% and 27% at the transport and depositional zone, respectively, in comparison to non-eroded soil. Overall, CO2 emission is the predominant form of C loss contributing to about 90.5% of total erosion-induced C losses in our 4-month experiment, which were equal to 18 g C m−2. Nevertheless, only 1.5% of the total redistributed C was mineralized to CO2 indicating a large stabilization after deposition. Our study also underlines the importance of C losses by particles and as DOC for understanding the effects of water erosion on the C balance at the interface of terrestrial and aquatic ecosystems.

Dissolved Organic Matter: Linking Soils and Aquatic Systems

Abstract: The guest editors introduce the contributions to the special section, Dissolved Organic Matter in Soil, with a focus on the three main directions in this complex and growing research effort. Dissolved organic matter (DOM) plays a crucial role in many important processes that take place in terrestrial and aquatic systems. These include carbon and nutrient cycling, pedogenesis, and microbial metabolism. Here we highlight the results of studies that demonstrate the role of DOM in linking terrestrial and aquatic systems. We emphasize three fundamental aspects of the research, which together show the importance of DOM in linking terrestrial and aquatic systems: First, tracing DOM properties during its transport through terrestrial and aquatic systems is a powerful tool for improving our conceptual understanding of the mechanistic drivers of DOM dynamics. Second, linking DOM dynamics to important physical processes such as hydrology provides important insights into the nature of terrestrial-aquatic links. Third, interrelations between DOM dynamics and human impacts on ecosystems highlight how the role of DOM in coupled terrestrial-aquatic systems may change in the future. New measurement and modeling approaches have enabled a more thorough assessment of all three aspects of DOM dynamics. They show that both natural and anthropogenic drivers not only greatly influence DOM dynamics in soils, but owing to the mobility of DOM, also have substantial influence on aquatic systems. This physical connection of soils and surface waters demonstrates the importance of understanding fundamental processes such as nutrient cycling, pedogenesis, and microbial metabolism at a whole-landscape scale.

N 2 O and CH 4 emission from soil amended with steam-activated biochar

Abstract: Steam-activation increased CH4 emission of stover biochar but decreased it for wood biochar by 14%–70%. Biochar generally increased CH4 emission but reduced N2O emission by 10%–41%. Emission of N 2 O was 17% lower for maize-stover biochar compared to Eucalyptus-wood biochar, and 3% lower for 350°C compared to 550°C pyrolysis temperature. Emission of CH 4 was 21% higher for activated stover biochar compared to Eucalyptus-wood biochar and 10% lower for 350°C compared to 550°C pyrolysis temperature. No difference in net CO 2 equivalent was observed among biochar grades.

The role of dissolved organic matter in adsorbing heavy metals in clay-rich soils

Abstract: Heavy metals (HMs) are toxic to human life and the environment when present in excessive concentrations. Therefore, determining the interactions of HMs with soils and dissolved organic matter (DOM) is essential to predict their fate. To find out the effect of DOM and soil properties (clay minerals, oxides, and bulk organic matter [OM]) on the uptake of Cu, Ni, and Zn, batch adsorption experiments were conducted using five soils sampled from Egypt. The sorption isotherms were well described by the initial mass (IM) isotherm model. The amount and timing of DOM addition was found to play a pivotal role in determining the affinity of the HMs for soil. When DOM and HMs were added simultaneously, the affinity of Cu decreased in Fe-(hydr)oxide-rich soils (by 7%) and increased in soils poor in Fe-(hydr)oxide (by 6–10%). When DOM was added first, followed by HMs, the affinity of Cu strongly increased. In contrast, affinity of both Ni and Zn was enhanced (3–18%) in the presence of DOM, regardless of the timing of DOM addition. The difference is explained by Cu binding to the solid phase and DOM through strong inner-sphere complexes, whereas Ni and Zn adsorbed predominantly through weaker electrostatic interactions. As a result, Cu was able to bind more strongly to previously adsorbed DOM on the solid phase in the case of smectite, while this effect was counteracted by the coating of available specific binding sites on Fe-(hydr)oxides. The study has revealed that Egyptian soils hold great potential to remove HMs from aqueous solutions.

Gone or Just out of Sight? the Apparent Disappearance of Aromatic Litter Components in Soils

Abstract: . Uncertainties concerning stabilization of organic compounds in soil limit our basic understanding on soil organic matter (SOM) formation and our ability to model and manage effects of global change on SOM stocks. One controversially debated aspect is the contribution of aromatic litter components, such as lignin and tannins, to stable SOM forms. In the present opinion paper, we summarize and discuss the inconsistencies and propose research options to clear them. Lignin degradation takes place stepwise, starting with (i) depolymerization and followed by (ii) transformation of the water-soluble depolymerization products. The long-term fate of the depolymerization products and other soluble aromatics, e.g., tannins, in the mineral soils is still a mystery. Research on dissolved organic matter (DOM) composition and fluxes indicates dissolved aromatics are important precursors of stable SOM attached to mineral surfaces and persist in soils for centuries to millennia. Evidence comes from flux analyses in soil profiles, biodegradation assays, and sorption experiments. In contrast, studies on composition of mineral-associated SOM indicate the prevalence of non-aromatic microbial-derived compounds. Other studies suggest the turnover of lignin in soil can be faster than the turnover of bulk SOM. Mechanisms that can explain the apparent fast disappearance of lignin in mineral soils are, however, not yet identified. The contradictions might be explained by analytical problems. Commonly used methods probably detect only a fraction of the aromatics stored in the mineral soil. Careful data interpretation, critical assessment of analytical limitations, and combined studies on DOM and solid-phase SOM could thus be ways to unveil the issues.

A novel high-temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. I: development and validation.

Abstract: RATIONALE: Traditionally, dissolved organic carbon (DOC) stable isotope analysis (SIA) is performed using either offline sample preparation followed by elemental analyzer/isotope ratiomass spectrometry (EA/IRMS) or a wet chemical oxidation (WCO)-based device coupled to an isotope ratio mass spectrometer. The first method is time-consuming and laborious. The second involves the risks of underestimation of DOC concentration and isotopic fractionation due to incomplete oxidation. The development of an analytical method for accurate and sensitive DOC SIA is described in this study. METHODS: A high-temperature combustion (HTC) system improves upon traditional methods. A novel total organic carbon (TOC) system, specially designed for SIA, was coupled to an isotope ratio mass spectrometer. An integrated purge and trap technique (peak focusing), flexible injection volume (0.05-3 mL), favorable carrier gas flow, modified ash crucible, new design of combustion tube and optimized drying system were used to achieve the necessary performance. RESULTS: The system can reliably measure concentrations up to 1000 mgC/L. Compounds resistant to oxidation, such as barbituric acid, melamine and humic acid, were analyzed with recovery rates of 100 +/- 1% proving complete oxidation. In this initial testing, the delta C-13 values of these compounds were determined with precision and trueness of CONCLUSIONS: 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. Copyright (C) 2014 John Wiley & Sons, Ltd.

A novel high-temperature combustion based system for stable isotope analysis of dissolved organic carbon in aqueous samples. : II optimization and assessment of analytical performance

Abstract: RATIONALE: Dissolved organic carbon (DOC) plays an important role in carbon cycling, making precise and routine measurement of delta C-13 values and DOC concentration highly desirable. A new promising system has been developed for this purpose. However, broad-scale application of this new technique requires an in-depth assessment of analytical performance, and this is described here. METHODS: A high-temperature combustion Total Organic Carbon analyzer was interfaced with continuous flow isotope ratio mass spectrometry (TOC/IRMS) for the simultaneous analysis of the bulk DOC concentration and delta C-13 signature. The analytical performance (precision, memory effects, linearity, volume/concentration effects, accuracy) was thoroughly evaluated, including realistic and challenging conditions such as low DOC concentrations and natural DOC. RESULTS: High precision (standard deviation, SD predominantly ≤0.15 ‰) and accuracy (R2 = 0.9997) were achieved for the δ13C analysis of a broad diversity of DOC solutions. Simultaneously, good results were obtained for the measurement of DOC concentration. Assessment of natural abundance and slightly 13C-enriched DOC, a wide range of concentrations (~0.2–150 mgC/L) and injection volumes (0.05–3 mL), demonstrated minor/negligible memory effects, good linearity and flexible usage. Finally, TOC/IRMS was successfully applied to determine low DOC concentrations (<2 mgC/L) and DOC from diverse terrestrial, freshwater and marine environments (SD ≤0.23 ‰). CONCLUSIONS: TOC/IRMS enables fast and reliable measurement of DOC concentrations and delta C-13 values in aqueous samples, without pre-concentration and freeze-drying. Further investigations should focus on complex, saline matrices and very low DOC concentrations, to achieve a potential lower limit of 0.2 mgC/L. Thus, TOC/IRMS will give DOC research in terrestrial and aquatic environments a huge impulse with high-resolution, routine delta C-13 analysis. Copyright (C) 2014 John Wiley & Sons, Ltd.

Response of Dissolved Organic Matter in the Forest Floor of a Temperate Spruce Stand to Increasing Throughfall

Abstract: In temperate spruce forests, dissolved organic matter (DOM) from forest floors is the major source of organic matter entering the mineral soil and thus it determines important soil properties and element cycling through the ecosystem. We examined effects of doubling locally collected throughfall for 6 yr on the concentrations of dissolved organic C (DOC) and properties of DOM (aromaticity, degree of molecule complexity) in the forest floor. Forest floor solutions below the Oi, Oe, and Oa horizons were sampled every 2 to 4 wk using tension lysimeters. For the controls, the average DOC concentrations in 2002 to 2007 were 43.8 ± 2.6 mg L −1 below the Oi, 49.6 ± 2.7 mg L −1 below the Oe, and 61.0 ± 2.0 mg L −1 below the Oa horizon. Doubling throughfall resulted in average DOC concentrations of 37.4 ± 1.8 mg L −1 (Oi), 49.3 ± 1.6 mg L −1 (Oe), and 50.1 ± 8.0 mg L −1 (Oa). The decreases in concentrations due to throughfall addition as well as the effects on DOM properties were, however, not statistically significant. It is commonly assumed that throughfall inputs are linearly related to water fluxes within and from the forest floor. Under that assumption, the results suggest that DOM fluxes are controlled by water fluxes rather than by the quantity of C that can be mobilized from the soil organic matter. Hence, increasing precipitation due to future climate changes presumably will result in enhanced DOM fluxes into the mineral horizons.

Mineralization of Eroded Organic Carbon Transported from a Loess Soil into Water

Abstract: The fate of soil-derived organic C (SOC) transported during erosion is a large uncertainty in assessing the impact of soil erosion on aquatic environments and in balancing C budgets. In our study, we determined C mineralization from solid soil organic C and dissolved organic C (DOC) translocated from a loess soil into surface water. We used runoff generated during rainfall simulation experiments. Both total runoff C and DOC were incubated to measure CO2 evolution during 28-d experiments. Cumulative CO2 emissions from runoff accounted for 3.9 to 4.8% of initial runoff C. It was estimated that 3.3 to 3.7% of initial solid SOC was mineralized contributing to 69 to 80% of total C mineralization from runoff. Mineralization of DOC was larger (7.3-30.2% of initial DOC) and showed a much larger variability than mineralization from solid SOC. However, DOC mineralization contributed to 20 to 31% of total C mineralization from runoff only because of the much smaller amounts of DOC than solid SOC. We could confirm a preferential removal of labile C from soils by water erosion. Nevertheless, the majority of this C will contribute to an aquatic C sink with less than 5% being potentially mineralizable. Our results indicated that the base level of C mineralization from translocated C was derived from the solid phase whereas the variability depends largely on DOC.

Dinámica del carbono en los ecosistemas de páramo de los Andes neotropicales: revisión de literatura sobre modelos y parámetros relevantes

Abstract: Resumen Los suelos del paramo almacenan cantidades excepcionales de carbono debido a las condiciones edaficas y climaticas sobre las cuales se desarrollan. Este gran reservorio de carbono esta amenazado debido a los efectos del cambio climatico y las dinamicas de uso de la tierra. No obstante, el desarrollo de mecanismos de mitigacion como los promovidos por REDD+ son una alternativa que puede ayudar a reducir los impactos de estas amenazas y promover su conservacion. Sin embargo, para la aplicacion de estos tipos de mecanismos es fundamental que los procesos asociados al mantenimiento y dinamica del ciclo del carbono sean comprendidos y los posibles impactos puedan ser proyectados. En este trabajo, a partir de una extensa revision de articulos indexados, se presenta una sintesis del estado actual del conocimiento y se discute las ventajas y limitaciones de la aplicacion de modelos de carbono organico del suelo y sus parametros asociados. Como resultado de esta revision, concluimos que los modelos disponibles actualmente contienen limitaciones importantes asociados a los procesos y flujos de la descomposicion de la materia organica que impiden su aplicacion en los paramos andinos. Adicionalmente, informacion sobre las variables de ingreso es limitada y lo mismo aplica para informacion independiente que permita validar los resultados modelados. El articulo concluye con recomendaciones sobre prioridades futuras de investigacion, enfatizando la urgencia del desarrollo de estudios comparativos sobre los efectos del uso de la tierra en la dinamica del carbono, en lugar del desarrollo de estudios experimentales en condiciones controladas. Abstract Paramo soils store exceptionally large amounts of carbon because of the specific edaphic and climatic conditions in tropical high-altitude ecosystems. This soil C-stock is threatened by changes in climate and land use, but potentials for its conservation on the basis of REDD+ type mechanisms are high. However, for application of such mechanisms it is crucial that properties and processes involved are adequately understood and impacts can be predicted. In this paper, an overview is given of the current knowledge and applicability of soil carbon models and parameters involved, based on a full search of publications in international refereed journals. The conclusion is that existing models are not readily applicable to paramo soils because of the specific decomposition processes and pathways. Moreover, information on relevant input parameters is scant and the same holds for data that can be used to validate model outputs. Recommendations are given for future research, emphasizing the urgency of comparative studies of land use impacts, rather than of experimental studies.

Stikstofkringloop in kalkrijke en kalkarme duinbodems

Abstract: SOURCE (OR PART OF THE FOLLOWING SOURCE): Type report Title Stikstofkringloop in kalkrijke en kalkarme duinbodems en de implicaties daarvan voor de effectiviteit van plaggen Author(s) A.M. Kooijman, J. Bloem, C. Cerli, G.A.J.M. Jagers op Akkerhuis, K. Kalbitz, K. Dimmers, A. Vos, A.K. Peest, R.H. Kemmers Faculty FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED), FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED), FNWI: Institute for Biodiversity and Ecosystem Dynamics (IBED) Year 2014