BayCEER Workshop 2023

Exploring the Role of the Riparian Zone in Subsurface Stormflow Transformation

P 3.6 in Zooming in: Small scale findings

Introduction:

Subsurface stormflow (SSF) significantly impacts streamflow in headwater catchments and undergoes transformations on its way from hillslopes to streams. These changes are driven by processes within the riparian zone, acting as a "reactor" where mixing, storage, and biogeochemical transformation of the hillslope SSF composition occur. However, a comprehensive understanding of the riparian zone’s "gatekeeper" function, controlling hydrological connectivity, timing, and chemistry transfer from hillslopes to streams, is still lacking.

Materials and Methods:

SSF signal transformation within riparian zones is investigated using a novel approach. Three "dual-use trenches" were installed in four German and Austrian catchments. This makes it possible to monitor SSF on hillslopes and introduce tracers into the riparian zone. We analyze the dynamics of the trench flow, as well as its chemical composition, aiming to identify tracers characterizing SSF for its subsequent identification in the riparian zone and in the stream. The influence of landscape and climate will be assessed by comparing the SSF response across catchments. Tracer injections combined with an extensive network of riparian wells allow the physical and chemical transformations of SSF in riparian zones to be investigated.

Results and Conclusions:

Our study presents the first data on the chemical signature of subsurface stormflow in the test catchments in the Black Forest region, Germany. The final goal of the study is to provide a conceptual framework for assessing SSF transformation in riparian zones with respect to catchment characteristics and hydrological conditions, which will deepen our understanding of riparian zone functionality.

Keywords: Riparian zone, subsurface stormflow, water chemistry, hydrological processes, tracer analysis