Advances in modelling hydrological dynamics in drained and cultivated peatlands

Process-modelling of hydrological dynamics in drained and cultivated fen soil profiles is essential for a precise calculation of greenhouse gas emissions. Until now, several estimation procedures exist, basically depending on site-specific conditions like land-use, vegetation, water table and fen soil type. To some extent these approaches are vulnerable to under- and overestimation of local greenhouse gas emissions by neglecting heterogeneous properties along fen soil profiles potentially differing from horizon to horizon. Hydrological modelling of water dynamics in fen soils characterised by progressed moorsh-forming process is restricted due to a lack of valid parameters describing available water retention functions. In the present study, a general applicable parameter set to solve the van Genuchten-Mualem water retention equation for fen soil horizons formed by drainage and cultivation has been developed based on a comprehensive dataset consisting of 520 horizontal data from fen soil profiles sampled at altogether 15 peatland areas in Germany. Different categorizations of the data were proofed to account for various states of peat decomposition and to reduce the range of measured volumetric soil water contents at specific pressure heads. Finally, bulk density was used as a cluster variable to consider the intensity of moorsh-forming process within every horizon category. Subsequent parameter estimation was conducted by the RETC programme and validation of the estimated parameters was realized for in total four monitoring plots varying in land-use type, climate and fen soil profile, by modelling water dynamics using HYDRUS-1d

Heißwasserextrahierbarer Kohlenstoff und Bodenatmung als Parameter zur Abschätzung der potentiellen Kohlenstofffreisetzung aus organischen Böden

Durch Ihre hohen Gehalte an Kohlenstoff (C) und organischer Bodensubstanz (OBS) und besitzen Moorböden eine herausragende Rolle im globalen Kohlenstoffkreislauf. Bei unsachgemäßer Nutzung setzen diese organischen Böden besonders hohe Mengen an C, z.B in Form von CO2 frei. Der labile und aktive Anteil der OBS, der potentiell besonders leicht freigesetzt werden kann, lässt sich allgemein mit dem Parameter heißwasserextrahierbarer Kohlenstoff (Chwe) abschätzen, da diese Fraktion große Mengen leicht umsetzbarer Bestandteile wie etwa hohe Anteile an mikrobieller Biomasse, Einfachzucker oder Ligninmonomere enthält. Bis jetzt ist aber unklar, wie gut sich dieser Parameter zur Ableitung der potentiellen C-Freisetzung aus Moorböden eignet. Für verschiedene Mineralböden konnten bereits enge Korrelationen zwischen dem Chwe und der jeweiligen Bodentamung aufgezeigt werden. Studien zur Beziehung der CO2-Freisetzung und dem Parameter Chwe speziell für organische Böden fehlen bisher. Ziel der vorliegenden Untersuchung war es deshalb, diese möglichen Korrelationen für organische Böden zu untersuchen. Dazu wurde der Chwe an über 50 unterschiedlichen Moorbodensubstraten ermittelt. Hier wurde eine Extraktionsmethode angewandt, welche speziell an die hohen Anteile an OBS angepasst wurde. Daneben wurde die jeweilige Bodenatmung mittels Inkubationsversuchen im Labor gemessen und mit dem Gehalt an Chwe verglichen. Die bisherigen Ergebnisse zeigen mittlere bis hohe Korrelationen zwischen der Bodenatmung und dem Chwe, so dass davon auszugehen ist, dass der Chwe zur Abschätzung einer potentiellen C-Freisetzung auch für organische Böden herangezogen werden kann, um damit die Empfindlichkeit gegenüber Kohlenstoffverlusten beschreiben zu können. Die gewonnenen Daten sollten allerdings durch zusätzliche Untersuchungen, vor allem an bisher nicht genügend berücksichtigten Moorbodensubstraten, weiter überprüft werden

Physical and hydrological properties of peat as proxies for degradation of South African peatlands: Implications for conservation and restoration

The physical and hydrological properties of peat from seven peatlands in northern Maputaland (South Africa) were investigated and related to the degradation processes of peatlands in different hydrogeomorphic settings. The selected peatlands are representative of typical hydrogeomorphic settings and different stages of human modification from natural to severely degraded. Nineteen transects (141 soil corings in total) were examined in order to describe peat properties typical of the distinct hydrogeomorphic settings. We studied degree of decomposition, organic matter content, bulk density, water retention, saturated hydraulic conductivity and hydrophobicity of the peats. From these properties we derived pore size distribution, unsaturated hydraulic conductivity and maximum capillary rise. We found that, after drainage, degradation advances faster in peatlands containing wood peat than in peatlands containing radicell peat. Eucalyptus plantations in catchment areas are especially threatening to peatlands in seeps, interdune depressions and unchannelled valley bottoms. All peatlands and their recharge areas require wise management, especially valley-bottom peatlands with swamp forest vegetation. Blocking drainage ditches is indispensable as a first step towards achieving the restoration of drained peatland areas, and further measures may be necessary to enhance the distribution of water. The sensitive swamp forest ecosystems should be given conservation priority

Impact of the spatial resolution of soils data on climate reporting for organic soils using the example of Germany

As a result of the climate conferences in Durban (2011) and Doha (2012), voluntary accounting for greenhouse gas emissions from organic soils is now possible in national climate reporting. The quality of the data describing the spatial extent of organic soils and their relevant soil properties thus becomes particularly important. For climate reporting issues, maps for organic soils at different scales and levels of detail are used. In Germany, for example, the soil map at scale 1:1,000,000 is the basis for the emission inventory (NIR 2013). In contrast, the national inventory report of The Netherlands is based on a soil map at scale 1:50,000 (Coenen et al. 2013). This leads to questions about the optimal level of detail or scale for climate reporting. Datasets with scales ranging from 1:25,000 up to 1:1,000,000 were used to derive the spatial distribution of organic soils in two characteristic areas of the temperate zone, one in northern and one in southern Germany. Comparison of the results shows large differences in both areal and spatial accuracy, depending on the origin and quality of the data as well as on scale and landscape characteristics. In southern Germany, for example, only 50 % of the organic soils derived from smaller-scale maps can be verified by detailed data, in contrast to more than 70 % in northern Germany. In combination with the partially poor spatial accuracy, these differences have a strong impact on the calculation of greenhouse gas emissions from organic soils, leading to errors of more than 60 %. As a result, for the temperate zone we recommend a minimum scale of 1:200,000 for maps of organic soils. However, in mountainous regions with higher geomorphic heterogeneity, more detailed data may be necessary

Non-equilibrium thermochemical heat storage in porous media: Part 1 – Conceptual model

Abstract Thermochemical energy storage can play an important role in the establishment of a reliable renewable energy supply and can increase the efficiency of industrial processes. The application of directly permeated reactive beds leads to strongly coupled mass and heat transport processes that also determine reaction kinetics. To advance this technology beyond the laboratory stage requires a thorough theoretical understanding of the multiphysics phenomena and their quantification on a scale relevant to engineering analyses. Here, the theoretical derivation of a macroscopic model for multicomponent compressible gas flow through a porous solid is presented along with its finite element implementation where solid–gas reactions occur and both phases have individual temperature fields. The model is embedded in the Theory of Porous Media and the derivation is based on the evaluation of the Clausius–Duhem inequality. Special emphasis is placed on the interphase coupling via mass, momentum and energy interaction terms and their effects are partially illustrated using numerical examples. Novel features of the implementation of the described model are verified via comparisons to analytical solutions. The specification, validation and application of the full model to a calcium hydroxide/calcium oxide based thermochemical storage system are the subject of part 2 of this study