Sulphide formation from granulite‐facies S‐rich scapolite breakdown

Scapolite in granulite facies terranes provides a reservoir for volatile components such as sulphur and carbon in rocks that are otherwise considered ‘dry’. Formed at lower crustal conditions, the high‐S end‐member of scapolite, silvialite, is a major host of sulphur in granulites. Compositional and textural changes involving scapolite reveal that S‐rich scapolite becomes unstable during hydration and deformation at amphibolite facies conditions. Either scapolite changes composition, whereby SO₄^2? is exchanged for CO₃^2? or Cl^? in its structure, or scapolite is replaced by amphibole and/or epidote. Sulphur that is released from silvialite is deposited as sulphides within the original silvialite grain boundaries and can remain relatively immobile in undeformed anorthosites. However, increased sulphide mobility is evident in areas of increased deformation and hydration. Reactions involving S‐bearing scapolite not only have important implications for sulphide deposition and the S‐cycle, but may also influence conductivity variation in the lower crust.     

Water balance,nutrient and carbon export from a heath forest catchment in central Amazonia,Brazil

Carbon storage values in the Amazon basin have been studied through different approaches in the last decades in order to clarify whether the rainforest ecosystem is likely to act as a sink or source for carbon in the near future. This water balance, dissolved organic carbon (DOC) and nutrient export study were carried out in a micro‐scale heath forest (Campina) catchment in central Amazonia, Brazil. For a 1‐year study period (18 March 2007 until 19 March 2008), rainfall amounted to 3054 mm; of which, 1532 mm was evaporated by the forest (4.1 mm day^?1). Rainfall interception loss amounted to 15.6% of gross rainfall. Surface runoff amounted to 485 mm, whereas another 1071 mm was discharged as regional groundwater outflow. Accumulated DOC exports in surface runoff amounted to 15.3 g m^?2 year^?1, whereas the total carbon exported was 55.9 g m^?2. This is much higher than that observed for a nearby tall rainforest catchment in central Amazonia (DOC export < 20 g m^?2). As Campina heath forest areas cover a significant proportion of the Amazon Basin, these differences in ecosystem hydrological carbon exports should be taken into account in future studies assessing the carbon budget for the Amazon Basin. Macro‐nutrient exports were low, but those of calcium and potassium were higher than those observed for tall rainforest in the Amazon, which may be caused by a lower retention capacity of the heath forest ecosystem. Copyright © 2015 John Wiley & Sons, Ltd.     

Economic geography as regional contexts’ reconsidered – implications for disciplinary division of labour,research focus and societal relevance

ABSTRACT

The aim of the article is to discuss whether a definition of economic geography as contextual analysis still is viable and relevant. The author argues that the definition remains the key to the production of high quality and social relevant research. He concludes that contextual analysis represents the competitive advantage of economic geography among other social sciences and the best position to demonstrate its relevance to the broader society.     

Where are the limits of model predictive capabilities?

Distributed hydrological models can make predictions with much finer spatial resolution than the supporting field data. They will, however, usually not have a predictive capability at model grid scale due to limitations of data availability and uncertainty of model conceptualizations. In previous publications, we have introduced the Representative Elementary Scale (RES) concept as the theoretically minimum scale at which a model with a given conceptualization has a potential for obtaining a predictive accuracy corresponding to a given acceptable accuracy. The new RES concept has similarities to the 25‐year‐old Representative Elementary Area concept, but it differs in the sense that while Representative Elementary Area addresses similarity between subcatchments by sampling within the catchment, RES focuses on effects of data or conceptualization uncertainty by Monte Carlo simulations followed by a scale analysis. In the present paper, we extend and generalize the RES concept to a framework for assessing the minimum scale of potential predictability of a distributed model applicable also for analyses of different model structures and data availabilities. We present three examples with RES analyses and discuss our findings in relation to Beven's alternative blueprint and environmental modeling philosophy from 2002. While Beven here addresses model structural and parameter uncertainties, he does not provide a thorough methodology for assessing to which extent model predictions for variables that are not measured possess opportunities to have meaningful predictive accuracies, or whether this is impossible due to limitations in data and models. This shortcoming is addressed by the RES framework through its analysis of the relationship between aggregation scale of model results and prediction uncertainties and for considering how alternative model structures and alternative data availability affects the results. We suggest that RES analysis should be applied in all modeling studies that aim to use simulation results at spatial scales smaller than the support scale of the calibration data.     

Spatial prediction on river networks: comparison of top‐kriging with regional regression

Top‐kriging is a method for estimating stream flow‐related variables on a river network. Top‐kriging treats these variables as emerging from a two‐dimensional spatially continuous process in the landscape. The top‐kriging weights are estimated by regularising the point variogram over the catchment area (kriging support), which accounts for the nested nature of the catchments. We test the top‐kriging method for a comprehensive Austrian data set of low stream flows. We compare it with the regional regression approach where linear regression models between low stream flow and catchment characteristics are fitted independently for sub‐regions of the study area that are deemed to be homogeneous in terms of flow processes. Leave‐one‐out cross‐validation results indicate that top‐kriging outperforms the regional regression on average over the entire study domain. The coefficients of determination (cross‐validation) of specific low stream flows are 0.75 and 0.68 for the top‐kriging and regional regression methods, respectively. For locations without upstream data points, the performances of the two methods are similar. For locations with upstream data points, top‐kriging performs much better than regional regression as it exploits the low flow information of the neighbouring locations. Copyright © 2012 John Wiley & Sons, Ltd.     

How to improve the representation of hydrological processes in SWAT for a lowland catchment – temporal analysis of parameter sensitivity and model performance

Model diagnostic analyses help to improve the understanding of hydrological processes and their representation in hydrological models. A detailed temporal analysis detects periods of poor model performance and model components with potential for model improvements, which cannot be found by analysing the whole discharge time series. In this study, we aim to improve the understanding of hydrological processes by investigating the temporal dynamics of parameter sensitivity and of model performance for the Soil and Water Assessment Tool model applied to the Treene lowland catchment in Northern Germany. The temporal analysis shows that the parameter sensitivity varies temporally with high sensitivity for three groundwater parameters (groundwater time delay, baseflow recession constant and aquifer fraction coefficient) and one evaporation parameter (soil evaporation compensation factor). Whereas the soil evaporation compensation factor dominates in baseflow and resaturation periods, groundwater time delay, baseflow recession constant and aquifer fraction coefficient are dominant in the peak and recession phases. The temporal analysis of model performance identifies three clusters with different model performances, which can be related to different phases of the hydrograph. The lowest performance, when comparing six performance measures, is detected for the baseflow cluster. A spatially distributed analysis for six hydrological stations within the Treene catchment shows similar results for all stations. The linkage of periods with poor model performance to the dominant model components in these phases and with the related hydrological processes shows that the groundwater module has the highest potential for improvement. This temporal diagnostic analysis enhances the understanding of the Soil and Water Assessment Tool model and of the dominant hydrological processes in the lowland catchment. Copyright © 2013 John Wiley & Sons, Ltd.     

Neotectonic deformation of a Late Weichselian outwash plain by deglaciation‐induced fault reactivation of a deep‐seated graben structure

The Late Weichselian Tinglev outwash plain in southwestern Denmark slopes gently from east to west, but certain areas of the topography show unusual irregularities. Analysis of LiDAR data reveals a mosaic of smaller areas with pronounced changes in slope magnitude and orientation between neighbouring areas. The outwash plain also features notable changes in elevation across kilometre‐long lineaments and areas lying lower and higher than the expected level. The depressions in the area have previously been interpreted as the result of melting dead‐ice blocks left by the Late Weichselian ice sheet. However, borehole samples from Lake Tinglev on the outwash plain show that lake sedimentation did not start until the early Holocene (9000 years ago), which is more than 9000 years after the ice sheet had retreated. The topographical irregularities are located above the Tønder Graben structure, and we interpret these as the result of Holocene strike‐slip movements along the graben faults resulting in areas of both subsidence and uplift. The deformations of the outwash plain are interpreted as the effect of deglaciation tectonics acting within a limited time frame at the beginning of the Holocene. As the event can be related to stress release from the weight of the Scandinavian Ice Sheet, we expect that other fault zones in northern Europe would be equally prone to reactivation. Tectonic events related to deglaciation would most likely be recurrent, and the stress changes appear to have been able to induce short‐lived tectonic instability to areas normally considered tectonically stable. We conclude that this type of tectonics has had a significant impact on topography and sedimentation throughout the Quaternary.