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Zusammenfassung und Fazit Über die im ROG ausgewiesenen Möglichkeiten, Minderungs-, Ausgleichs- und Ersatzmaß-nahmen in die Entwicklung der anzustrebenden Freiraumstruktur einzubinden sowie mittels der entsprechenden Aussagemöglichkeiten v. a. der überörtlichen Landschaftsplanung las-sen sich für die Eingriffsregelung Verknüpfungen zur regionalen Ebene herstellen. Nicht nur die viel beklagte und durch exemplarische Auswertungen des brandenburgischen Eingriffs- und Kompensationsflächenkatasters (EKIS) z. T. auch tatsächlich nachweisbare Zersplitte-rung der Kompensationsflächen, sondern auch künftige Anforderungen zur Umsetzung eines Biotopverbunds nach $ 3 BNatSchG und der europäischen Wasserrahmenrichtlinie sowie die Sicherung des kohärenten Netzes NATURA 2000 machen die Notwendigkeit deutlich, die rechtlich angelegten Möglichkeiten einer übergreifenden, auf regionaler Ebene ansetzenden Lenkung von Kompensationsmaßnahmen stärker auszuschöpfen. Gesehen werden muss jedoch auch, dass ein solches stärker konzeptionell ("Top- down") bestimmtes Herangehen zwar fachlich wünschenswert ist, konkrete Erfahrungen aus der wissenschaftlichen Begleitung zum regionalen Flächenpool "Kulturlandschaft Mittlere Havel" jedoch darauf hindeuten, dass bei der Konzeption und Umsetzung regionaler Flächenpools zwei naturschutzfachliche Ebenen zu unterscheiden sind: Zum Einen besagte konzeptionell-strategische Planung und Vorbereitung auf der Zielebene, zum Anderen die Klärung der Ver-fügbarkeit einzelner Flächen und die konkrete, ins Detail gehende Maßnahmenplanung. Es ist wohl nur eingeschränkt realistisch, regionale Flächenpools ausschließlich über eine hie-rarchische "Top-down-Steuerung" mittels der Maßgaben von Landschaftsplanung und Raumordnung zu installieren, sondern im Gegenzug müssen im konkreten Flächenbezug die Klärung standörtlicher Flächeneignungen, der jeweiligen Flächenverfügbarkeiten, die Entwicklung örtlicher Projektgebiete sowie kooperative Verhandlungen mit den einzelnen örtli-chen Akteuren und Grundstückseigentümern erfolgen. Daraus lässt sich die Forderung ablei-ten, dass in der Diskussion um regionale Flächenpools neben der konzeptionellen Steuerung der Ebene der konkreten Maßnahmenspezifizierung und -durchführung verstärkte Aufmerk-samkeit gewidmet werden sollte, um im Zusammenwirken von "Top-Down"- und "Bottom- up"-Ansätzen zu einem effektiven Kompensationsmanagement zu gelangen.
At present, carbon sequestration in terrestrial ecosystems slows the growth rate of atmospheric CO2 concentrations, and thereby reduces the impact of anthropogenic fossil fuel emissions on the climate system. Changes in climate and land use affect terrestrial biosphere structure and functioning at present, and will likely impact on the terrestrial carbon balance during the coming decades - potentially providing a positive feedback to the climate system due to soil carbon releases under a warmer climate. Quantifying changes, and the associated uncertainties, in regional terrestrial carbon budgets resulting from these effects is relevant for the scientific understanding of the Earth system and for long-term climate mitigation strategies. A model describing the relevant processes that govern the terrestrial carbon cycle is a necessary tool to project regional carbon budgets into the future. This study (1) provides an extensive evaluation of the parameter-based uncertainty in model results of a leading terrestrial biosphere model, the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM), against a range of observations and under climate change, thereby complementing existing studies on other aspects of model uncertainty; (2) evaluates different hypotheses to explain the age-related decline in forest growth, both from theoretical and experimental evidence, and introduces the most promising hypothesis into the model; (3) demonstrates how forest statistics can be successfully integrated with process-based modelling to provide long-term constraints on regional-scale forest carbon budget estimates for a European forest case-study; and (4) elucidates the combined effects of land-use and climate changes on the present-day and future terrestrial carbon balance over Europe for four illustrative scenarios - implemented by four general circulation models - using a comprehensive description of different land-use types within the framework of LPJ-DGVM. This study presents a way to assess and reduce uncertainty in process-based terrestrial carbon estimates on a regional scale. The results of this study demonstrate that simulated present-day land-atmosphere carbon fluxes are relatively well constrained, despite considerable uncertainty in modelled net primary production. Process-based terrestrial modelling and forest statistics are successfully combined to improve model-based estimates of vegetation carbon stocks and their change over time. Application of the advanced model for 77 European provinces shows that model-based estimates of biomass development with stand age compare favourably with forest inventory-based estimates for different tree species. Driven by historic changes in climate, atmospheric CO2 concentration, forest area and wood demand between 1948 and 2000, the model predicts European-scale, present-day age structure of forests, ratio of biomass removals to increment, and vegetation carbon sequestration rates that are consistent with inventory-based estimates. Alternative scenarios of climate and land-use change in the 21<sup>st century suggest carbon sequestration in the European terrestrial biosphere during the coming decades will likely be on magnitudes relevant to climate mitigation strategies. However, the uptake rates are small in comparison to the European emissions from fossil fuel combustion, and will likely decline towards the end of the century. Uncertainty in climate change projections is a key driver for uncertainty in simulated land-atmosphere carbon fluxes and needs to be accounted for in mitigation studies of the terrestrial biosphere.
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