Impact of the unsaturated zone in the hydrochemical and hydrodynamical functioning of karst aquifer: example of the Tlemcen Mountains, Northwest Algeria

• Published in: Arabian journal of geosciences Vol. 11; no. 16; pp. 1 - 17
• Main Authors: Azzaz, H., Emblanch, C., Bekkoussa, B. S., Hamimed, A., Khaldi, A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2018; Springer Nature B.V
• Subjects: Aeration zone; Aquifers; Calcium; Calcium ions; Carbon 14; Carbon dioxide; Drainage systems; Earth and Environmental Science; Earth science; Earth Sciences; Infiltration; Karst; Magnesium; Mountains; Open systems; Original Paper; Residence time; Soil; Total organic carbon; Tracers; Unsaturated flow; Variation; Unsaturated zone; Algeria; Tlemcen Mountains; Karst; Hydrochemical; Isotopes
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-018-3824-8

The aim of this work is to understand the role of unsaturated zone on the functioning of karst aquifers. The easy infiltration of water into the system explains the expansion of karstification through the saturated zone. The unsaturated zone is largely involved in the flow on the overall karstic system. For this purpose, we use the environmental tracing, namely the calco-carbonic equilibrium elements (CO
2
, CO
3
2−
, HCO
3
−
, Ca
2+
, Mg
2+
), TOC, and isotopic elements (
14
C,
13
C, and
3
H) interesting tracers of residence time. Result obtained from TOC and Mg
2+
enabled us to classify the behavior of systems to fissured type with a low average and restricted fluctuation of TOC concentrations and relatively high Mg
2+
(inertial system). The second functioning type is characterized by a very high average and important variation of TOC with low contents of Mg
2+
(perched system with fast infiltration). The values of
3
H and
14
C allow to distinguish three categories of water (old, mixture actual-old, and actual) with the predominance of actual waters. The comparison of the measured δ
13
C with those calculated shows that the majority of the karstic aquifers of Tlemcen Mountains are open systems with respect to the soil biogenic CO
2
. The piston flow in the unsaturated zone puts in charge the drains and stops drainage in the lower part of the system. The direct participation of infiltration is relatively low for all systems.