Poster, DyCap Workshop "Microbiology and Reactive Transport in the Capillary Fringe" (October 7-8, 2010), Heidelberg: 07.10.2010 - 08.10.2010
In mountainous catchments wetlands often make up large fractions of the total catchment area with potential implications for runoff generation and nutrient export. Wetland surfaces are often characterized by a distinct micro-topography (hollows and hummocks). The effects of such micro-topography on surface-subsurface exchange, runoff generation and sub-surface residence times for a 10 by 20 m synthetic section of a riparian wetland are investigated in this modeling study. The structure of the micro-topography replicates that of a riparian wetland in a small mountainous catchment in South-East Germany (Lehstenbach) and is created using geostatistical simulation. Flow is modeled with the fully integrated surface-subsurface code HydroGeoSphere. Simulation results show that the specific structure of the wetland surface results in distinct shifts between surface and subsurface flow dominance. The micro-topography efficiently buffers rainfall inputs and produces a hydrograph that is characterized by subsurface drainage during most of the year and only temporally shifts to surface flow dominance during intense rainstorms. Micro-topography induces a very heterogeneous sub-surface hydrology where a shallow and a deep flow system coexist resulting in a very complex sub-surface residence time distribution. Preliminary results show that the complex sub-surface flow field, with its broad range of different sub-surface flow paths, leads to biogeochemical patchiness.