22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Changes of the isotopic signatures and hydrochemistry in the unsaturated zone detected by a precision lysimeter installed in a dune belt (Doñana National Park, southwest Spain)

27 Sep 2019, 11:45
15m
Auditorium 2 ()

Auditorium 2

Oral Topic 5 - Tools, methods and models to study groundwater Parallel

Speaker

Mr Fernando Ruíz (Geological Survey of Spain IGME)

Description

In September 2015, a high precision weighing meteolisimeter of 1.5 m height and a surface of 1 m2 with lower boundary control was installed in the coastal dune belt of the Doñana National Park, southwest Spain. The infiltrated rainwater in the lysimeter has been drained into a drainage vessel. Both the lysimeter and the vessel weight have been recorded every minute. This study presents hydrogeochemical and isotope data of rain and drained water of the lysimeter to investigate water-rock-interaction in the unsaturated zone and to evaluate the possible effects of evaporation and condensation as well as mixing processes and residence times of the drainage water. Between October 2015 and June 2018 the content of δ2H and δ18O was analyzed in 49 water samples (21 rain and 28 drainage water). Additionally, between May 2017 and April 2018, hydrochemical analyzes of major components were also carried out in 10 rainwater samples and 8 samples of the drainage vessel. The results show a high variability of the rainwater composition ranging from Ca-Mg-HCO3 to NaCl-type. The water in the drainage vessel ranges between NaCl and CaSO4 types. Based on the isotope data, a local meteoric line (LMWL) has been derived. The LMWL presents a lower slope than the Global Meteoric Water Line (GMWL), while the lysimeter water line (drained water) plots below the LMWL, with less data variability than rainwater. The different position of the lysimeter waterline points to (i) additional fractionation processes of percolating rainwater in the unsaturated zone or (ii) a second water source different from rainwater related to condensation of vapor with a more humid origin than rainwater. The importance of vapor adsorption was already detected by the evolution of the Lysimeter weights yielding daily amounts between 0.3 and 0.5 mm in periods without rain. Future work will consist in analyzing the isotopic content of δ2H and δ18O of the atmospheric vapor, condensed vapor and pore water of the unsaturated zone in the vicinity of the lysimeter to quantify the possible contribution of this component.

Primary authors

Mr Fernando Ruíz (Geological Survey of Spain IGME) Claus Kohfahl Dr Iñaki Vadillo-Pérez (Grupo de Hidrogeología, Departamento de Ecología y Geología, Facultad de Ciencias, Universidad de Málaga)

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