Journal of Ecological Engineering Received: 2018.10.04 Revised: 2018.11.13 Volume 20, Issue 3, March 2019, pages 112–125 Accepted: 2019.01.10 Available online: 2019.01.20 https://doi.org/10.12911/22998993/99743 Natural Isotopes and Ion Compositions Identify Changes in Groundwater Flows Affecting Wetland Vegetation in the Drentsche Aa Brook Valley, The Netherlands Samer Elshehawi1,2,*, Enno Bregman3,4, Paul Schot5, Ab Grootjans1,6 1 Centre for Energy and Environmental Studies, University of Groningen, The Netherlands. 2 Centre for Isotope Research, University of Groningen, The Netherlands. 3 Province of Drenthe, The Netherlands. 4 Physical Geography Department, University of Utrecht, The Netherlands. 5 Copernicus Institute of Sustainable Development, University of Utrecht, The Netherlands. 6 Institute of Water and Wetland Research, Radboud University Nijmegen, The Netherlands. * Corresponding author’s e-mail:
[email protected] ABSTRACT This study uses groundwater isotopes and ion composition to verify model simulations and ecohydrological stud- ies in the Drentsche Aa nature reserve in The Netherlands, which is representative for the northwestern wetland areas in the Ice Marginal Landscape zone. At eight field sites, a total of 24 samples were analysed for their 13C, 14C, 2H, and 18O isotopes and ionic composition. The isotopes indicate that most of the fen peatlands in the area depend on the exfiltration of sub-regional groundwater flows, which confirmed the previous model simulations and ecohydrological studies. At three sites, isotopes and ionic composition indicate that the groundwater from the sub-regional system has been replaced by local infiltrated rainwater, due to nearby groundwater abstractions for drinking water, which influenced the success rates of the restoration measures.