Drainage of peatlands for agriculture causes an increase of C0 2 flux from peat decomposition, contributing to national C0 2 emission. The reverse process, i.e. for re-creation of wetlands, reduces the C0 2 flux, but increases the CH4 flux. We developed a process model (PEATLAND) to simulate these fluxes from peat soils subject to different water-table management scenarios. The model combines primary production, aerobic decomposition of soil organic matter (including the soil-parent material, peat), CH4 formation, oxidation, and transport. Model input requires specification of water table and air temperature data sets, vegetation parameters such as primary production and parameters related to gas transport, and basic soil physical data.Validation using closed flux-chamber measurements of C0 2 and CH4 from five different sites in the western Netherlands shows that seasonal changes in fluxes of C0 2 and CH4 are correctly modelled. However, the C0 2 submodel underestimates peat decomposition when peat decomposition rates obtained from laboratory incubation experiments are used as input. Field decomposition rates are considerably higher. This is attributed to enhancement of decomposition by the addition of easily decomposable material from root exudation ('priming effect'). Model experiments indicate that 1) drainage increases the C0 2 production from peat decomposition strongly; 2) restoring a high water table may decrease the total greenhouse gas flux by a small amount although the CH4 flux increases strongly; 3) a warmer climate may cause higher greenhouse gas fluxes from peat soils resulting in a positive feedback to climate warming, and 4) high vegetation productivity in fen meadows may stimulate peat decomposition by the priming effect.

The dominant processes concept was used to develop a regionally applicable rainfall-runoff model. The first-order runoff processes are identified through a combination of field investigations, physico-geographical analysis of the research area, the Alzette River basin in the Grand-Duchy of Luxembourg, and discharge data series analysis. Lithology appeared to be the major source of discrepancy in hydrological behaviour over the total area. As a result, the hydrological behaviour of each lithological substratum was characterized and conceptualized into a parsimonious model structure. The runoff signals were calibrated against the hourly-recorded discharge series of eight sub-basins, with parameter sensitivity and correlation analysis outlining the need for minor corrections to the model structure. Validation against another set of 10 sub-basins showed good results for the regional parameter set, with an average loss in efficiency (R eff ) of 0.04, compared to the reference model, with a mean R eff of 0.79. Due to an up-scaling effect, inducing variations in the dominance of particular runoff processes, some anomalies were found in the performance of individual runoff characteristics. In this respect, limiting the application of the model to a certain spatial scale gives a high reliability of the prediction of the dynamics of hourly runoff in ungauged basins within the study area.Modélisation régionalisée des débits au moyen de l'aggrégation de connaissances sur les processus hydrologiques de premier ordre : une étude de cas Résumé Le concept des processus dominants a été utilisé afin de développer un modèle pluie-débit au champ d'application régional. Les processus d'écoulement de premier ordre sont identifiés à travers un ensemble d'expérimentations sur le terrain, une analyse des caractéristiques physio-géographiques de la zone d'étude, à savoir le bassin de l'Alzette au Grand-Duché de Luxembourg, ainsi qu'une analyse de séries de débits. La lithologie est l'origine principale des différences de comportement hydrologique sur la zone d'étude. Ainsi, le fonctionnement hydrologique propre à chaque substrat géologique a été caractérisé et conceptualisé dans une structure de modèle parcimonieux. Les paramètres des modèles ont été calés au moyen de séries de débits horaires issus de huit sous-bassins. L'analyse de sensibilité des paramètres et l'examen des liens entre ces paramètres ont mis en évidence l'intérêt de corrections mineures sur la structure initiale du modèle pour une application régionale. La validation sur un deuxième lot de 10 sous-bassins a donné de bons résultats pour le jeu de paramètres régionalisé. Le passage d'une échelle spatiale à une autre modifie la prédominance des processus. Ceci explique les moindres performances des modèles sur certains bassins versants. En conséquence, il est conseillé de limiter l'application du modèle à une échelle spatiale donnée pour garantir une prévision fiable de la dynamique de l'écoulement horaire dans des bassins versants non-jaugés à l'intérieur de la zone d'étu...

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Drained coastal peatlands are a source of greenhouse gas (GHG) through abundant C0 2 release caused by aerobic peat degradation. Published rates of C0 2 fixation and CH 4 release for natural peatlands suggest that areas of peat formation are a (small) net source of GHG emission because the radiative effect of emitted CH 4 exceeds the C0 2 uptake by the vegetation. It is shown here that wetland restoration of reclaimed peat areas in the western Netherlands leads to a reduction of GHG emission because the expected increase in anaerobically generated CH 4 release is much smaller than the decrease in aerobically produced C0 2 .

Abstract:In this study a simple modelling approach was applied to identify the need for spatial complexity in representing hydrological processes and their variability over different scales. A data set of 18 basins was used, ranging between 8 and 4011 km 2 in area, located in the Nahe basin (Germany), with daily discharge values for over 30 years. Two different parsimoniously structured models were applied in lumped as well as in spatially distributed according to two distribution classifications: (1) a simple classification based on the lithology expressed in three permeability types and (2) a more complex classification based on seven dominating runoff production processes. The objective of the study was to compare the performances of the models on a local and on a regional scale as well as between the models with a view to identifying the accuracy in capturing the spatial variability of the rainfall-runoff relationships. It was shown that the presence of a specific basin characteristic or process of the distribution classification was not related with higher model performance; only a larger basin size promoted higher model performance. The results of this study also indicated that the permeability generally contained more useful information on the spatial heterogeneity of the hydrological behaviour of the natural system than did a more detailed classification on dominating runoff generation processes. Although model performance was slightly lower for the model that used permeability as a distribution classification, consistency in its parameter values was found, which was lacking with the more complex distribution classification. The latter distribution classification had a higher flexibility to optimize towards the variability of the runoff, which resulted in higher performance, however, process representation was applied inconsistently.