Kriterien für die Zertifizierung von Kohlenstoffsenken in Landwirtschaftsböden

Im Rahmen der Klimadiskussion sind auch CO2-Zertifikate* für die Einlagerung von Kohlenstoff in Landwirtschaftsböden (Kohlenstoffsenken) im Gespräch. Doch bevor solche Zertifikate ausgegeben werden, muss sichergestellt werden, dass die Kohlenstoffsenken zu einer effektiven Reduktion von Klimagasen beitragen. Damit dies geschehen kann, müssen vier Kriterien erfüllt sein

Critères de certification pour les puits de carbone dans les sols agricoles

Les certificats* de CO2 peuvent théoriquement être attribués pour les puits de carbone dans les sols agricoles et font l’objet de discussions dans le cadre du débat sur le climat. Mais avant que ces certificats ne puissent être délivrés, il faut s’assurer que les puits de carbone dans les sols contribuent à une réduction effective des gaz à effet de serre. Pour cela, quatre critères devraient être remplis

Restricting the nonlinearity parameter in soil greenhouse gas flux calculation for more reliable flux estimates

The static chamber approach is often used for greenhouse gas (GHG) flux measurements, whereby the flux is deduced from the increase of species concentration after closing the chamber. Since this increase changes diffusion gradients between chamber air and soil air, a nonlinear increase is expected. Lateral gas flow and leakages also contribute to non linearity. Several models have been suggested to account for this non linearity, the most recent being the Hutchinson±Mosier regression model (HMR). However, the practical application of these models is challenging because the researcher needs to decide for each flux whether a nonlinear fit is appropriate or exaggerates flux estimates due to measurement artifacts. In the latter case, a flux estimate from the linear model is a more robust solution and introduces less arbitrary uncertainty to the data. We present the new, dynamic and reproducible flux calculation scheme, KAPPA.MAX, for an improved trade-off between bias and uncertainty (i.e. accuracy and precision). We develop a tool to simulate, visualise and optimise the flux calculation scheme for any specific static N2O chamber measurement system. The decision procedure and visualisation tools are implemented in a package for the R software. Finally, we demonstrate with this approach the performance of the applied flux calculation scheme for a measured flux dataset to estimate the actual bias and uncertainty. The KAPPA.MAX method effectively improved the decision between linear and nonlinear flux estimates reducing the bias at a minimal cost of uncertainty

Dynamic stability of mineral-associated organic matter: enhanced stability and turnover through organic fertilization in a temperate agricultural topsoil

Soil organic matter (SOM) plays a vital role for soil quality, sustainable food production and climate change mitigation. It is common knowledge that SOM consists of different pools with varying qualities, quantities, and turnover times. However, it is still poorly understood how mineral and organic fertilization affects the formation and stabilization of mineral-associated organic matter (MAOM) and how long it can remain there. Here, we report on the long-term effects of different farming systems on the stability and turnover of the fine silt and clay-sized MAOM fraction (<6.3 μm) of a Haplic Luvisol (0–20 cm) in the DOK long-term trial (Switzerland). We compared three farming systems with contrasting fertilization (CONMIN = pure mineral, CONFYM = mineral + organic, BIODYN = pure organic) with an unfertilized control (NOFERT) between 1982 and 2017. We performed specific surface area (SSA) measurements on fractionated MAOM samples (<6.3 μm) from 1982 to 2017, before and after removal of OM, measured the 14C activity of all samples during the entire period and estimated the mean residence time (MRT) with a model taking into account ‘bomb 14C’ and radioactive decay. We found constant MAOM-C contents under organic fertilization. Results of SSA analysis indicate best conditions for MAOM-C stabilization under organic fertilization and different sorption mechanisms in MAOM between farming systems with and without organic fertilization. The modelled MRTs were significantly higher in NOFERT (238 ± 40 yrs) and CONMIN (195 ± 27 yrs), compared to CONFYM (138 ± 18 yrs) and BIODYN (140 ± 19 yrs), implying a high C turnover (i.e. more active MAOM) at high C contents under organic fertilization. Our findings show that MAOM is not the dead OM but corroborates the concept of ‘dynamic stability’. Continuous OM inputs from organic fertilizers and their rapid and constant turnover are needed to stabilize the “stable” MAOM-C fraction

Turnover of grassland roots in mountain ecosystems revealed by their radiocarbon signature: role of temperature and management

Root turnover is an important carbon flux component in grassland ecosystems because it replenishes substantial parts of carbon lost from soil via heterotrophic respiration and leaching. Among the various methods to estimate root turnover, the root’s radiocarbon signature has rarely been applied to grassland soils previously, although the value of this approach is known from studies in forest soils. In this paper, we utilize the root’s radiocarbon signatures, at 25 plots, in mountain grasslands of the montane to alpine zone of Europe.We place the results in context of a global data base on root turnover and discuss driving factors. Root turnover rates were similar to those of a subsample of the global data, comprising a similar temperature range, but measured with different approaches, indicating that the radiocarbon method gives reliable, plausible and comparable results. Root turnover rates (0.06–1.0 y-1) scaled significantly and exponentially with mean annual temperatures. Root turnover rates indicated no trend with soil depth. The temperature sensitivity was significantly higher in mountain grassland, compared to the global data set, suggesting additional factors influencing root turnover. Information on management intensity from the 25 plots reveals that root turnover may be accelerated under intensive and moderate management compared to low intensity or semi-natural conditions. Because management intensity, in the studied ecosystems, co-varied with temperature, estimates on root turnover, based on mean annual temperature alone, may be biased. A greater recognition of management as a driver for root dynamics is warranted when effects of climatic change on belowground carbon dynamics are studied in mountain grasslands.KB received support from the Swiss National Science Foundation, project 200021-115891 (www.snf.ch). SM received support from the Swiss State Secretariat for Education and Research, project C07.0031 (www.sbfi.admin.ch). MTS received support from the Spanish Ministry of Science and Innovation, (project CAPAS, CGL2010-22378-C03- 01) (www.idi.mineco.gob.es)

Effects of Land-Use Change on Carbon Stocks in Switzerland

We assessed how consequences of future land-use change may affect size and spatial shifts of C stocks under three potential trends in policy—(a) business-as-usual: continuation of land-use trends observed during the past 15years; (b) extensification: full extensification of open-land; and (c) liberalization: full reforestation potential. The build-up times for the three scenarios are estimated at 30, 80 and 100years, respectively. Potential C-stock change rates are derived from the literature. Whereas the business-as-usual scenario would cause marginal changes of 0.5%, liberalization would provoke a 13% increase in C stocks (+62MtC). Gains of 24% would be expected for forests (+95MtC), whereas open-land C stock would decrease 27% (−33MtC). Extensification would lead to a C stock decrease of 3% (−12MtC). Whereas forest C is expected to increase 12% (+36.5MtC) at high elevations, stocks of open-land C would decline 38.5% (−48.5MtC). Most affected are unfavorable grasslands, which increase in area (+59%) but contribute only 14.5% to the C stocks. C sinks would amount to 0.6MtCy−1 assuming a build-up time of 100years for the liberalization scenario. C stocks on the current forest area are increasing by 1MtCy−1. The maximal total C sink of 1.6MtC might thus suffice to compensate for agricultural greenhouse gases (2004: 1.4Mt CO2-C equivalents), but corresponds only to 11-13% of the anthropogenic greenhouse gas emission in Switzerland. Thus, even the largest of the expected terrestrial C stocks under liberalization will be small in comparison with current emissions of anthropogenic greenhouse gase

Organochemical Characterization of Peat Reveals Decomposition of Specific Hemicellulose Structures as the Main Cause of Organic Matter Loss in the Acrotelm

Peatlands store carbon in the form of dead organic residues. Climate change and human impact impose risks on the sustainability of the peatlands carbon balance due to increased peat decomposition. Here, we investigated molecular changes in the upper peat layers (0-40 cm), inferred from high-resolution vertical depth profiles, from a boreal peatland using two-dimensional H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy, and comparison to delta C-13, delta N-15, and carbon and nitrogen content. Effects of hydrological conditions were investigated at respective sites: natural moist, drainage ditch, and natural dry. The molecular characterization revealed preferential degradation of specific side-chain linkages of xylan-type hemicelluloses within 0-14 cm at all sites, indicating organic matter losses up to 25%. In contrast, the xylan backbone, galactomannan-type hemicelluloses, and cellulose were more resistant to degradation and accumulated at the natural moist and drainage site. delta C-13, delta N-15, and carbon and nitrogen content did not correlate with specific hemicellulose structures but reflected changes in total carbohydrates. Our analysis provides novel insights into peat carbohydrate decomposition and indicates substantial organic matter losses in the acrotelm due to the degradation of specific hemicellulose structures. This suggests that variations in hemicellulose content and structure influence peat stability, which may have important implications with respect to climate change

Peatland protection and restoration are key for climate change mitigation

Peatlands cover only about 3% the global land area, but store about twice as much carbon as global forest biomass. If intact peatlands are drained for agriculture or other human uses, peat oxidation can result in considerable CO2 emissions and other greenhouse gases (GHG) for decades or even centuries. Despite their importance, emissions from degraded peatlands have so far not been included explicitly in mitigation pathways compatible with the Paris Agreement. Such pathways include land-demanding mitigation options like bioenergy or afforestation with substantial consequences for the land system. Therefore, besides GHG emissions owing to the historic conversion of intact peatlands, the increased demand for land in current mitigation pathways could result in drainage of presently intact peatlands, e.g. for bioenergy production. Here, we present the first quantitative model-based projections of future peatland dynamics and associated GHG emissions in the context of a 2 °C mitigation pathway. Our spatially explicit land-use modelling approach with global coverage simultaneously accounts for future food demand, based on population and income projections, and land-based mitigation measures. Without dedicated peatland policy and even in the case of peatland protection, our results indicate that the land system would remain a net source of CO2 throughout the 21st century. This result is in contrast to the outcome of current mitigation pathways, in which the land system turns into a net carbon sink by 2100. However, our results indicate that it is possible to reconcile land use and GHG emissions in mitigation pathways through a peatland protection and restoration policy. According to our results, the land system would turn into a global net carbon sink by 2100, as projected by current mitigation pathways, if about 60% of present-day degraded peatlands would be rewetted in the coming decades, next to the protection of intact peatlands

Peatland protection and restoration are key for climate change mitigation

Peatlands cover only about 3% the global land area, but store about twice as much carbon as global forest biomass. If intact peatlands are drained for agriculture or other human uses, peat oxidation can result in considerable CO2 emissions and other greenhouse gases (GHG) for decades or even centuries. Despite their importance, emissions from degraded peatlands have so far not been included explicitly in mitigation pathways compatible with the Paris Agreement. Such pathways include land-demanding mitigation options like bioenergy or afforestation with substantial consequences for the land system. Therefore, besides GHG emissions owing to the historic conversion of intact peatlands, the increased demand for land in current mitigation pathways could result in drainage of presently intact peatlands, e.g. for bioenergy production. Here, we present the first quantitative model-based projections of future peatland dynamics and associated GHG emissions in the context of a 2 °C mitigation pathway. Our spatially explicit land-use modelling approach with global coverage simultaneously accounts for future food demand, based on population and income projections, and land-based mitigation measures. Without dedicated peatland policy and even in the case of peatland protection, our results indicate that the land system would remain a net source of CO2 throughout the 21st century. This result is in contrast to the outcome of current mitigation pathways, in which the land system turns into a net carbon sink by 2100. However, our results indicate that it is possible to reconcile land use and GHG emissions in mitigation pathways through a peatland protection and restoration policy. According to our results, the land system would turn into a global net carbon sink by 2100, as projected by current mitigation pathways, if about 60% of present-day degraded peatlands would be rewetted in the coming decades, next to the protection of intact peatlands.DFG Priority Program “Climate Engineering: Risks, Challenges, Opportunities?” (SPP 1689)Horizon 2020 Framework Programmehttp://dx.doi.org/10.13039/100010661Peer Reviewe