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Runoff generation mechanisms

Field studies in one of the sub-catchments, Studibach, focus on understanding runoff generation mechanisms (i.e., how rainfall and snowmelt become streamflow) in steep mountain catchments underlain by low permeability soils. After extensive studies on groundwater levels and groundwater chemistry, current work focuses on near surface flow pathways: overland flow and subsurface flow through the organic rich topsoil layer. This work (2021-2024) involves the installation of runoff plots, stream monitoring, tracer experiments, and rainfall simulation experiments.

Contact: Anna Leuteritz, Victor Gauthier, Dr. Ilja van Meerveld (Uni Zurich)

 

Stream network expansion and contraction – patterns, controls and importance

Temporary streams are common and represent a substantial portion of the total stream network. However, they are generally not included in stream monitoring networks. As a result, little is known about the hydrological responses of temporary streams and the factors that control the occurrence of flow in temporary streams, or how the onset of flow in temporary streams affects streamflow and water quality in perennial streams.
Two projects in the Alptal study how and when connectivity between flowing sections of the temporary stream network is established, what spatial and temporal controls there are on the occurrence of streamflow and stream network expansion in temporary mountain headwater streams, and how this influences spatial and temporal variations in streamflow and water quality in perennial streams. This is done by detailed field monitoring.

Contact: Rick Assendelft and Dr. Ilja van Meerveld (Uni Zürich), Izabela Bujak and Dr. Jana von Freyberg (EPFL)

 

Channel-bed monitoring using SfM and Photosieving

Investigations of streambed characteristics contribute to a better understanding of sediment transport processes which occur during flood hydrographs. In the Erlenbach, the methods Structure from Motion and Photo Sieving have been applied in two channel reaches with lengths of 100 m and 170 m. This approach has been used to determine (i) the streambed topography and (ii) the grain size distribution of the surface layer of the streambed after each flood event, when the bed was relatively dry. Two different methods are tested for taking photos, namely with a drone camera and with a camera at the top of an aluminum rod. As part of a master's thesis, the feasibility of the methods was tested and their accuracy was investigated in 2020. Further observations are planned for the coming season.

Kontakt: Dieter Rickenmann und Florian Käslin (WSL)

 

Nitrogen dynamics Alptal

Nitrogen deposition is a potential threat for forests as it can affect the equilibrium between plant nutrients and disturb the botanical composition of the herb layer. Too much nitrogen can also lead to nitrate leaching into surface waters. In a long-term experiment in a very small headwater catchment, we add ammonium nitrate to rain water sprinkled over the ground vegetation. We study the fate of this added nitrogen and its effects on soil (including greenhouse gas exchanges), plants and water. Results so far show an accumulation of nitrogen in the soil, but with relatively small effects on plants in general and a slight improvement of tree growth in particular. Nitrate leaching from the treated catchment increased compared to a control catchment. This was especially the case when part of the trees were cut because production by mineralisation in the soil plus deposition then clearly exceeded plant demand for nitrogen.

Kontakt: Patrick Schleppi (WSL)

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Role of intermittency in the trophic relations of macroinvertebrates in Alptal streams

Flow intermittency is becoming more common in many stream networks with major effects on the biodiversity and food webs of macroinvertebrates. This study examines the trophic relations of macroinvertebrates along the stream network of Erlenbach and Studibach in the Alptal. Both systems show some degree of flow intermittency along the stream network. Macroinvertebrates are collected at different sites across seasons for assessment of biodiversity (distribution and abundance) and trophic structure using stable carbon and nitrogen isotopes. Data collected will eventually be upscaled to reveal spatio-temporal patterns along both stream networks and interpreted from a functional perspective.

Kontakt: Christopher T. Robinson, Carmen Kowarik and Christa Jolidon (Eawag)

 

Spatial and temporal variability of snow processes under different vegetation covers

Within the DFG-project SPENSER we investigate the temporal and spatial variability of snow depth and snow water equivalent within different forest types and structure. Therefore, we are developing and testing a novel LiDAR (Multi-Wavelength) system mounted on a fixed wing UAV. UAV surveys will be carried out throughout the season for deriving differential snow-depth maps. The results will be combined with data from 40 snow monitoring stations that capture meteorological parameters and snow depth each hour. The data will be made available to the scientific community and used for a model comparison study and for deriving forest structure indices that allow an upscaling on catchment scales.

Kontakt: Joschka Geissler und Markus Weiler (Uni Freiburg i.Br.)