Hydrogeochemical and multi-tracer investigations of arsenic-affected aquifers in semi-arid West Africa
Autor: | Franck Lalanne, Elaheh Ghadiri, Massimo Rolle, Matthias S. Brennwald, Lucien Stolze, Anja Bretzler, Julien Nikiema, Mario Schirmer |
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Jazyk: | angličtina |
Rok vydání: | 2019 |
Předmět: |
010504 meteorology & atmospheric sciences
Groundwater chemistry Geochemistry Aquifer engineering.material 010502 geochemistry & geophysics Monsoon Residence time (fluid dynamics) 01 natural sciences Arsenic West Africa 0105 earth and related environmental sciences Arsenopyrite geography geography.geographical_feature_category Fractured aquifers Residence time lcsh:QE1-996.5 Arid Water level Noble gases lcsh:Geology visual_art engineering visual_art.visual_art_medium General Earth and Planetary Sciences Environmental science Pyrite Groundwater |
Zdroj: | Bretzler, A, Stolze, L, Nikiema, J, Lalanne, F, Ghadiri, E, Brennwald, M S, Rolle, M & Schirmer, M 2019, ' Hydrogeochemical and multi-tracer investigations of arsenic-affected aquifers in semi-arid West Africa ', Geoscience Frontiers, vol. 10, no. 5, pp. 1685-1699 . https://doi.org/10.1016/j.gsf.2018.06.004 Geoscience Frontiers, Vol 10, Iss 5, Pp 1685-1699 (2019) Geoscience Frontiers, 10 (5) |
Popis: | The semi-arid Sahel regions of West Africa rely heavily on groundwater from shallow to moderately deep (10 μg/L) stemming from the oxidation of sulphide minerals (pyrite, arsenopyrite) in mineralised zones. These aquifers are still little investigated, especially concerning groundwater residence times and the influence of the annual monsoon season on groundwater chemistry. To gain insights on the temporal aspects of As contamination, we have used isotope tracers (noble gases, 3H, stable water isotopes (2H, 18O)) and performed hydrochemical analyses on groundwater abstracted from tube wells and dug wells in a small study area in southwestern Burkina Faso. Results revealed a great variability in groundwater properties (e.g. redox conditions, As concentrations, water level, residence time) over spatial scales of only a few hundred metres, characteristic of the highly heterogeneous fractured underground. Elevated As levels are found in oxic groundwater of circum-neutral pH and show little relation with any of the measured parameters. Arsenic concentrations are relatively stable over the course of the year, with little effect seen by the monsoon. Groundwater residence time does not seem to have an influence on As concentrations, as elevated As can be found both in groundwater with short (103 a) residence times as indicated by 3He/4He ratios spanning three orders of magnitude. These results support the hypothesis that the proximity to mineralised zones is the most crucial factor controlling As concentrations in the observed redox/pH conditions. The existence of very old water portions with residence times >103 years already at depths of Geoscience Frontiers, 10 (5) |
Databáze: | OpenAIRE |
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