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The central topic of this dissertation is the 3D spatial description of geomorphic and sediment mass balance development in initial phases of ecosystem development. The introductory chapters give an overview on the consideration of characteristics and relevance of the initial development phase in geomorphological landform development concepts and summarize the state of the art of research for experimental studies on landform development and for 3D soil-landscape modeling approaches. The central aim of the work is a 3D-spatially and temporally resolved description of the development of mass balances of the sediment solid phase during the initial years of ecosystem development and of its dependence on initial and boundary conditions in the 6 ha, artificially-created catchment ‘Hühnerwasser’. This aim is approached using remotely-sensed data, methods of quantitative soil landscape modeling and geomorphic change detection, and the application of a numerical landscape evolution model. The construction of a 3D volume model of the catchment’s sediment body based on digital elevation data is described. Possibilities for the quantification of sediment mass balances and for the 3D spatial description of sediment properties within this model are discussed. Digital elevation models based on airborne and terrestrial laser scanning and photogrammetry are evaluated for their suitability for sediment mass balance quantification and reconstruction of initial morphologic development; and methods for the modification and combination of elevation data for improved sediment mass balance quantification are described. The development of the catchment’s surface morphometry and of the geometry of the evolving erosion rill network is reconstructed and analysed based on aerial photographs and digital elevation models. Relations between structures of the initial surface and the developing hydro-geomorphic structures are discussed. Effects of initial surface morphology and precipitation characteristics during the initial development phase are further assessed by simulations with a numeric landscape evolution model. Results allow for a quantification of geometry and volume of the catchment’s initial sediment body and for a visualization of sediment layers deposited in time intervals. It is shown that a combination of different elevation data, based on their suitability for depicting the sediment surface in areas of different morphologic and vegetation characteristics, allows for an improved quantification of sediment mass balances. Results allow for a characterization of phases of rill network growth, contraction and stabilization and suggest influences of initial morphology, precipitation characteristics, and developing structure-process-interactions on rill network geometry in the catchment. The phases of hydro-geomorphic surface structure evolution can be related to the spatial organization of surface flow patterns during initial phases of landform development.
Processes of microbial carbon transformation and accumulation during initial stream succession were investigated. Studies were carried out in the experimental watershed Chicken Creek, constructed to investigate ecosystem succession, and additionally in experimental flumes simulating sand-bed streams. In a one year investigation, microbial respiration in soils and sediments along the hydrologic flow path of three stream corridors in the Chicken Creek watershed was measured. Contrary to expectation, respiration rates of rewetted soil and sediment from dry stream channels were similar to rates measured with sediments collected in the perennial channel sections. This suggested that permanent water availability was not a main factor determining metabolic potential in this early successional watershed. In an outdoor flume experiment it was determined whether shallow (1cm) and deep (4cm) sediment disturbances in small sand-bed streams have similar effects on whole-stream metabolism, and whether autotrophic and heterotrophic processes and organisms respond in similar ways. Results suggested that disturbing sediments during early successional stages had no effect on whole-stream metabolism, whereas in advanced stages, deep but not shallow sediment disturbance could lead to a transitory shift towards heterotrophy. Changes in riparian and in-stream vegetation during stream succession come along with different amounts and types of organic matter input in stream ecosystems. It was tested to determine if increasing quality and quantity of litter input changes whole-stream metabolism and activity and structure of microbial communities associated with sediments and leaves. Whole-stream metabolism was found to be similar in all treatments because sediments and leaves were constrained by oxygen and nutrient availability. There seemed to be compensation between the effect of algae fueling microbial activity in open-land treatments and microbial use of allochthonous carbon sources in the litter treatments. Fungal and bacterial activity associated with leaves was unaffected by the background litter standing stock, but the structure of communities was affected. However, leaf quality had a clear effect on microbial activity and community structure with higher activity on tree compared to grass leaves.