Characterizing the groundwater contribution to ecologically valuable lowland streams using travel time distributions

Groundwater is the main source of stream flow for many lowland streams and therefore affecting the abiotic habitat conditions of aquatic ecosystems. The groundwater contribution to streams influences (1) river discharge, (2) water quality, (3) temperature and (4) the riparian zone. The input of groundwater provides streams with a stable base flow, good quality water and a steady temperature. However, the groundwater contribution to streams is often not characterized in detail. The current research addresses the groundwater input and its importance for aquatic ecology in lowland streams and aims to characterize it in a more sophisticated way using dynamic Travel Time Distributions. A 3D groundwater flow model (MODFLOW) was used to characterize daily Travel Time Distributions in the Dinkel lowland catchment in The Netherlands. This revealed varying contributions of groundwater flow paths with different travel times. Longer and shorter flow paths differ in amount and timing of flow, hydrochemistry and temperature. Results can be used to study the effect of stresses on the groundwater component of stream flow, and the aquatic ecosystems and habitats present in the stream.