Water and ion movement through a minicatchment at Risdalsheia, Norway (RAIN project)

Abstract

At Risdalsheia (Southernmost Norway) the relation between flow paths and streamwater chemistry through a small headwater catchment was investigated. The importance of these pathways for the interaction between soil solution and runoff chemistry was investigated by a tracer experiment with LiBr. The experiment was designed using all available information about ion transport at EGIL-catchment in a simple model that predicted the breakthrough curve for a given tracer input. The unique facility of a roofed catchment allowed attainment and maintainace of a hydrological steady-state under highflow conditions during this tracer experiment. The chemical changes of the moving soil water due to soil/soil solution interaction mainly occured during vertical (unsaturated) infiltration. Most ions reached their runoff concentration levels after these few cm of vertical infiltration. Only the ions SO4, NO3, and H increased along the saturated lateral flow path. Subsurface, translatory flow and equilibrum reactions along vertical infiltration flow paths are the key process that explain the behavior of stormflow chemistry at the EGIL-catchment.