Institut für Geographie und Geoökologie
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Veränderung der Abflüsse
(2005)
Reductions in river discharge (water availability) like those from climate change or increased water withdrawal, reduce freshwater biodiversity. We combined two scenarios from the Intergovernmental Panel for Climate Change with a global hydrological model to build global scenarios of future losses in river discharge from climate change and increased water withdrawal. Applying these results to known relationships between fish species and discharge, we build scenarios of losses (at equilibrium) of riverine fish richness. In rivers with reduced discharge, up to 75% (quartile range 4-22%) of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. Fish loss in the scenarios fell disproportionately on poor countries. Reductions in water consumption could prevent many of the extinctions in these scenarios
This paper examines the effect of spatially variable initial soil moisture and spatially variable precipitation on predictive uncertainty of simulated catchment scale runoff response in the presence of threshold processes. The underlying philosophy is to use a physically based hydrological model named CATFLOW as a virtual landscape, assuming perfect knowledge of the processes. The model, which in particular conceptualizes preferential flow as threshold process, was developed based on intensive process and parameter studies and has already been successfully applied to simulate flow and transport at different scales and catchments. Study area is the intensively investigated Weiherbach catchment. Numerous replicas of spatially variable initial soil moisture or spatially variable precipitation with the same geostatistical properties are conditioned to observed soil moisture and precipitation data and serve as initial and boundary conditions for the model during repeated simulations. The effect of spatially soil moisture on modeling catchment runoff response was found to depend strongly on average saturation of the catchment. Different realizations of initial soil moisture yielded strongly different hydrographs for intermediate initial soil moisture as well as in dry catchment conditions; in other states the effect was found to be much lower. This is clearly because of the threshold nature of preferential flow as well as the threshold nature of Hortonian production of overland flow. It was shown furthermore that the spatial pattern of a key parameter (macroporosity) that determined threshold behavior is of vast importance for the model response. The estimation of these patterns, which is mostly done based on sparse observations and expert knowledge, is a major source for predictive model uncertainty. Finally, it was shown that the usage of biased, i.e. spatially homogenized precipitation, input during parameter estimation yields a biased model structure, which gives poor results when used with highly distributed input. If spatially highly resolved precipitation was used during model parameter estimation. the predictive uncertainty of the model was clearly reduced. (c) 2005 Elsevier B.V. All rights reserved
A fine-grained slope that exhibits slow movement rates was investigated to understand how geohydrological processes contribute to a consecutive development of mass movements in the Vorarlberg Alps, Austria. For that purpose intensive hydrometeorological, hydrogeological and geotechnical observations as well as surveying of surface movement rates were conducted during 1998-2001. Subsurface water dynamics at the creeping slope turned out to be dominated by a three-dimensional pressure system. The pressure reaction is triggered by fast infiltration of surface water and subsequent lateral water flow in the south-western part of the hillslope. The related pressure signal was shown to propagate further downhill, causing fast reactions of the piezometric head at 5.5 m depth on a daily time scale. The observed pressure reactions might belong to a temporary hillslope water body that extends further downhill. The related buoyancy forces could be one of the driving forces for the mass movement. A physically based hydrological model was adopted to model simultaneously surface and subsurface water dynamics including evapotranspiration and runoff production. It was possible to reproduce surface runoff and observed pressure reactions in principle. However, as soil hydraulic functions were only estimated on pedotransfer functions, a quantitative comparison between observed and simulated subsurface dynamics is not feasible. Nevertheless, the results suggest that it is possible to reconstruct important spatial structures based on sparse observations in the field which allow reasonable simulations with a physically based hydrological model. Copyright (c) 2005 John Wiley & Sons, Ltd
One of the mechanisms for sudden particle release is a decrease in groundwater salt concentration to below the critical salt concentration (CSC), where repulsion forces between fine particles and matrix surfaces exceed binding forces. In this paper, an attempt was made to determine the CSC with both batch and column experiments. Two types of sediments were tested: (a) homogeneous quartz sand and (b) mineralogically heterogeneous sediment, taken from the Hanford formation in southeast Washington. Stepwise decreasing concentrations of NaNO3 solution were applied until fine particles were released from the sediments and the CSC was determined. Two methods were used to minimize the interference of particle release due to physical forces (shear stress) in the batch experiments: (a) postexperimental correction for mechanical effects, and (b) minimization of shear stress on the sediments during the experiment. CSCs from batch experiments were compared to those obtained from column experiments. It was found that both the amount of particles released and the CSC were an order of magnitude higher for the Hanford sediment than for the Sand. Moreover, particle detachment above the CSC was observed for the Hanford sediment. This suggests that the concept of sharp CSCs could be problematic in natural heterogeneous sediments where fine particles may mobilize at salt concentrations significantly above the CSC, thus unexpectedly enhancing colloid-facilitated transport of contaminants. (C) 2004 Elsevier B.V. All rights reserved
Flussauen stellen in der Bundesrepublik Deutschland seit langem ein gemeinsames Handlungsfeld von Naturschutz und Wasserwirtschaft dar. Nachdem mit der EG-Wasserrahmenrichtlinie (WRRL) eine Neuausrichtung der Gewässerentwicklung in den Mitgliedsstaaten eingeleitet worden ist, stellt sich auch die Frage, welche neuen Ansätze sich den Beteiligten in Bezug auf die Flussauen eröffnen. Welche Bedeutung hat das Gewässerumfeld und mit ihm die Flussauen - für das Erreichen der von der WRRL gesteckten Umweltziele, und wie verändert die Umsetzung der WRRL die Voraussetzungen für den Naturschutz in Flussauen? Da die Wasserrahmenrichtlinie den Begriff "Flussaue" nicht verwendet, werden zunächst die relevanten Regelungen der Richtlinie herausgearbeitet, die einen deutlichen Bezug zu den Naturschutzbelangen in Flussauen erkennen lassen. An zwei Beispielgebieten mit verschiedenen naturräumlichen Bedingungen und unterschiedlichem Ausbauzustand der Gewässer, der "Unteren Havelniederung" und dem "Südlichen Oberrhein", werden - bezogen auf die Anforderungen der WRRL - Gemeinsamkeiten und Unterschiede der Handlungsansätze von Wasserwirtschaft und Naturschutz veranschaulicht. Darauf aufbauend werden schließlich 16 Empfehlungen für die Zusammenarbeit von Naturschutz und Wasserwirtschaft bei der Umsetzung der WRRL formuliert. Die Handlungsempfehlungen richten sich gleichermaßen an den behördlichen Naturschutz und die Naturschutzverbände wie auch an die mit der Umsetzung der Wasserrahmenrichtlinie befassten Behörden der Wasserwirtschaft. Es zeichnet sich ab, dass Naturschutz und Wasserwirtschaft sich bei der Umsetzung ihrer Ziele in Flussauen gegenseitig unterstützen können. Die Beteiligten erhalten konkrete Anregungen, wie die vorhandenen Synergiepotenziale bestmöglich ausgeschöpft werden können.