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| Titel |
Identifying hydrological pathways in the north basin of Lake Kivu using stable isotope ratios of meteoric recharge and surface water |
| VerfasserIn |
Charles M. Balagizi, Marcellin M. Kasereka, Stefan Terzerand, Emilio Cuoco, Marcello Liotta |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129585
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| Publikation (Nr.) |
 EGU/EGU2016-9720.pdf |
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| Zusammenfassung |
| A rain-gauge network of 12 stations was installed at different altitudes at Nyiragongo volcano
(DR Congo) and surroundings and sampled on monthly basis between December 2013 and
June 2015 to evaluate the isotopic signature of the meteoric recharge. Additional samples
were collected on monthly basis from 5 rivers, 7 springs, 3 profiles in Kabuno bay and 2
others in the Main Basin of Lake Kivu to determine their water isotope compositions (δ18O
and δ2H). The precipitation, surface and groundwater δ18O and δ2H values were
thereafter used to estimate the groundwater recharge area, surface and groundwater
inflow level to Lake Kivu, and for modeling water circulation in the north basin of
Lake Kivu. The monthly precipitation isotope composition varied in a large range,
whereas mean precipitation-weighed values ranged between -12.39‰ and 6.52‰ for
δ2H, and from -4.02‰ to -0.91‰ for δ18O. Monthly values allowed to define a
Local Meteoric Water Line of equation δ2H=7.96δ18O + 16.96. Our dataset, the
first time series in the Virunga, implies that the δ18O and δ2H of precipitation are
predominantly determined by the recycled moisture source area, while their clearly defined
seasonality is driven by wind direction and precipitation amount changes. The δ18O,
δ2H and deuterium-excess values revealed a convergence zone around Nyiragongo
where the N-NE and S-SW trade winds come together. Moisture from the Nile
River basin brought by the N-NE originating winds yielded depleted precipitation
at local highlands, while that from the Congo River basin brought by the S-SW
wind yielded enriched precipitation at lowlands. Rivers and springs monthly are
included in the range of monthly precipitation values, and are thus indicative of lack of
significant evaporation during aquifer recharge. The mean rivers and springs δ2H and
δ18O, and the mean precipitation-weighed values revealed the presence of shallow
groundwater recharged between 2100 and 2700m a.s.l., and deep groundwater recharged at
up to 3100 m. Both Kabuno Bay and the Main Basin of the CO2- and CH4-rich
permanently stratified Lake Kivu (485m maximum depth) showed highly enriched
surface waters. However the values significantly decrease with depth and were
thus lower at the bottom. The δ2H and δ18O data revealed that subaerial rivers and
shallow groundwater discharge in the upper layer of Lake Kivu, while the deep
groundwater reaches the lake as lateral cold and hot springs inflows to the water column as
well as hydrothermal water at the floor. Water of the upper layer of Lake Kivu is
highly enriched by intense surface evaporation, whereas the intense water-rock
interactions and hydrothermal activities within the aquifers could be responsible for the
enrichment of waters transferred to the deep permanently stratified layer of Lake Kivu |
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