Publikationsdatum:
2023-03-20
Beschreibung:
The δ18O and δ2H of rivers and springs were investigated in order to characterize the groundwater recharge
sources around Nyiragongo and Nyamulagira volcanoes, in the Democratic Republic of the Congo and Rwanda.
Water samples were collected monthly between November 2013 and October 2014 from 5 major rivers, 3 major
cold springs, 3 tepid springs and 1 hot spring. The temperatures of each spring were nearly constant over the
sampling period attesting for their groundwater character, while the temperatures of the rivers were much more
variable. The rivers monthly δ2H and δ18O range from 6.8‰ to 1.9‰ and 3.1‰ to 1.6‰, respectively, while
springs showed depleted values that span from 10.2 to 1.1‰ for δ2H and 3.6 to 1.9‰ for δ18O. Catchment
morphology (formed of depression, upper footslope and medium to high gradient-mountains) and the local
tectonic discontinuity (fissures and faults) regulate the surface runoff and subsurface flow, control the precipitation
infiltration zones and hence the aquifers recharge areas. Chemical and isotopic (δ18O and δ2H) compositions
of springs and rivers reveal the presence of shallow and deep aquifers, with some waters having
intermediate isotope composition. Three different recharge zones characterized by different altitudes were
identified: the first is found at low altitude ranging from ~1800 m to ~2150 m, the second and intermediate
recharge zone in the altitude range from ~2180 m to ~2500 m at the upper footslope area, while the third and
highest recharge area is located in the altitudes range from ~2620 to ~3220 m. The two upper recharge areas are
the most fractured and fissured zones allowing rapid infiltration of depleted precipitations which recharge deep
aquifers found in the tepid and hot springs. Based on their chemical and isotopic composition, waters from the
shallow and deep aquifers have been considered representative of mixing end members. During their ascent to
the surface, water from the deep aquifer mixes with that of shallow aquifer yielding the tepid springs of intermediate
chemical and isotopic composition, while the other keep their original fingerprint corresponding to the
isotopically depleted hot spring.
Beschreibung:
Published
Beschreibung:
120778
Beschreibung:
6A. Geochimica per l'ambiente e geologia medica
Beschreibung:
JCR Journal
Repository-Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Materialart:
article
