During initial phases of landform evolution, the surface of sediment bodies is commonly not yet equilibrated with the environmental conditions and is thus liable to rapid changes by accelerated geomorphic activity. Hydro-geomorphic processes acting during these early development phases often lead to the emergence of surface structures that constitute the boundary conditions for further ecosystem development, and of linear erosion features that act as pathways for water, solute and sediment transport, and thus can increase the system's connectivity. Studies on initial landform evolution are often limited to relatively small-scale experiments or rely on modeling exercises. Larger-scale experiments can be carried out in constructed hydrological catchments with well-known and documented initial conditions. The central aim of this work was to describe the hydro-geomorphic surface structure evolution during the initial years of ecosystem development, its dependence on initial and boundary conditions; and on its relations to hydro-geomorphic connectivity. The data are from the 6-ha, constructed hydrological catchment 'Hühnerwasser'. Hydro-geomorphic development was quantified using a combined analysis of digital elevation models and aerial photographs. Empirical results were compared with those obtained with a numerical landscape evolution model. Phases of rill network growth, contraction and stabilization could be characterized. Results show influences of initial morphology, precipitation characteristics, and developing structure-process-interactions on rill network geometry and connectivity increase in the catchment. The results suggest that phases of hydro-geomorphic surface structure evolution can be related to the spatial organization of surface flow patterns during initial phases of landform development.
During initial phases of landform evolution, the surface of sediment bodies is commonly not yet equilibrated with the environmental conditions and is thus liable to rapid changes by accelerated geomorphic activity. Geomorphic processes acting during these early development phases depend on the initial sediment composition and the subsurface and surface structures of the geosystem; at the same time, these processes lead to landscape structures that constitute boundary conditions for further ecosystem development.
Knowledge about spatial heterogeneity is of essential for the analysis of the hydrological catchment behavior.
Heterogeneity is directly related to the distribution of the solid phase, and in initial hydrological systems, the
solid phase is mainly composed of mineral particles. In artificial catchments, such sediment structures relate to
the applied construction technology. It is supposed that the development of catchment ecosystems is strongly
influenced by such specific initial spatial distributions of the solid phase. Moreover, during the initial development
period, the primary structures in a catchment are altered rapidly by translocation processes, thereby subdividing
the initial system in different compartments. Questions are: How does initial sediment distribution affect further
structural development? How is catchment hydrology influenced by the initial structural development? What
structures have a relevant impact on catchment-scale hydrological behavior?
Variability of rainfall and throughfall is an essential characteristic of the water balance at spatial scales ranging from meters to hundreds of meters or even kilometers. The amount of throughfall is governed by the characteristics of the vegetation canopy and the involved interception and stemflow effects. In initial, developing ecosystems, distinct patterns of the growing vegetation (e.g. patchiness) supposedly govern the spatial distribution of water in the system, thereby initiating and supporting hydro-ecological feedback processes. Questions are i) is the spatial variability of vegetation relevant for the system as a whole, and ii) how does the distribution of the effective precipitation (i.e. the infiltration) change over time in dependency of vegetation succession?
We present the first results of a spatially distributed measurement approach of surface-near precipitation on the constructed catchment “Hühnerwasser” (“Chicken Creek”). The 6-ha site is located in the recultivation area of the lignite open-cast mine “Welzow-Süd” in Lower Lusatia, Brandenburg, Germany. Here, the free development of an initial ecosystem is investigated since September 2005. After eight years of succession, the spatial distribution of plant species is highly heterogeneous, and gains increasing influence on throughfall patterns, thus impacting the distribution of soil humidity and possibly even surface runoff.
For spatially distributed precipitation measurement, 47 tipping bucket rain gauges were installed in heights of 0.5 m and 1.0 m along two transects on the catchment. Rain gauge data were collected by a wireless sensor node network provided by the Sens4U joint research project. The transects run NW-SE and NE-SW and cover the range of plant communities presently existing in the ecosystem: locust copses, dense sallow thorn bushes and reeds, base herbaceous and medium-rise small-reed vegetation, and open areas covered by moss and lichens. The raw measurement data were temporally aggregated using a VBA script in order to characterize interception for various types of precipitation events on different time scales.
First results from the measurement period 17th July – 3rd September 2013 widely exhibit a good accordance with reference data from on-site weather stations for sites on open ground, while canopy sites show more heterogeneous values, either due to interception or due to canopy collection effects. However, it was found that the explanation of the differences between comparable sites requires an additional inclusion of other relevant parameters, e.g. wind speed and direction, screening effects, and specific canopy characteristics. Moreover, extreme precipitation events sometimes seemed to lead to incorrect measurements either by the sensor and / or node, which required supplementary quality controls of equipment and data.
Results from future long-term measurements on the “Hühnerwasser” catchment will be used to identify possible plant-soil feedback mechanisms and to parameterize models that simulate the behavior of initial eco-hydrological systems