Comparison of the Dynamics of the Flowing Drainage Network and Water Chemistry for Four Headwater Catchments

Abstract

The re-emergence of water in dry stream reaches affects streamwater chemistry due to the flushing of sediment and nutrients from previously dry channels and the increased connectivity between hillslopes and streams. Although these processes have been studied at the reach scale, field data on stream network dynamics and hydrochemistry at the catchment scale are rare. We studied the temporal changes in the flowing drainage network (FDN) and hydrochemistry for two 5-ha catchments in the Swiss pre-Alps and two 25- to 32-ha catchments on the Swiss Plateau. At each site, one catchment was relatively flat and had an extensive stream network augmented by artificial ditches, while the other catchment was relatively steep and had a shorter stream network where flow was maintained by springs. The dynamics of the FDN differed substantially for the geomorphologically different catchments in each region, despite their proximity, comparable size, soil and bedrock characteristics. Hydrochemistry and FDN were more dynamic in the flatter catchments with the extensive but shallow channels and ditches. For these catchments, nitrate mobilisation and a notable ‘first flush’ of solutes were observed during most rainfall events. Hydrochemistry and FDN remained relatively stable in the steeper catchments fed by perennial springs. These results highlight the notable spatial variations in stream chemistry responses to precipitation events and the insights that can be gained by joint observations of the FDN and hydrochemical dynamics.