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| Titel |
Characterisation of stable isotopes to identify residence times and runoff components in two meso-scale catchments in the Abay/Upper Blue Nile basin, Ethiopia |
| VerfasserIn |
S. Tekleab, J. Wenninger, S. Uhlenbrook |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 6 ; Nr. 18, no. 6 (2014-06-26), S.2415-2431 |
| Datensatznummer |
250120397
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| Publikation (Nr.) |
 copernicus.org/hess-18-2415-2014.pdf |
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| Zusammenfassung |
Measurements of the stable isotopes oxygen-18 (18O) and deuterium
(2H) were carried out in two meso-scale catchments, Chemoga
(358 km2) and Jedeb (296 km2) south of Lake Tana, Abay/Upper Blue
Nile basin, Ethiopia. The region is of paramount importance for the water
resources in the Nile basin, as more than 70% of total Nile water flow
originates from the Ethiopian highlands. Stable isotope compositions in
precipitation, spring water and streamflow were analysed (i) to characterise the spatial and temporal variations of
water fluxes; (ii) to estimate the mean residence time of water using a sine
wave regression approach; and (iii) to identify runoff components using
classical two-component hydrograph separations on a seasonal timescale.
The results show that the isotopic composition of precipitation exhibits
marked seasonal variations, which suggests different sources of moisture
generation for the rainfall in the study area. The Atlantic–Indian Ocean,
Congo basin, Upper White Nile and the Sudd swamps are the potential moisture
source areas during the main rainy (summer) season, while the Indian–Arabian
and Mediterranean Sea moisture source areas during little rain (spring) and
dry (winter) seasons. The spatial variation in the isotopic composition is
influenced by the amount effect as depicted by moderate coefficients of
determination on a monthly timescale (R2 varies from 0.38 to 0.68) and
weak regression coefficients (R2 varies from 0.18 to 0.58) for the
altitude and temperature effects. A mean altitude effect accounting for
−0.12‰/100 m for 18O and −0.58‰/100 m for
2H was discernible in precipitation isotope composition.
Results from the hydrograph separation on a seasonal timescale indicate the
dominance of event water, with an average of 71 and 64% of the total
runoff during the wet season in the Chemoga and Jedeb catchments,
respectively.
Moreover, the stable isotope compositions of streamflow samples were damped
compared to the input function of precipitation for both catchments. This
damping was used to estimate mean residence times of stream water of 4.1 and
6.0 months at the Chemoga and Jedeb catchment outlets, respectively. Short
mean residence times and high fractions of event water components recommend
catchment management measures aiming at reduction of overland flow/soil
erosion and increasing of soil water retention and recharge to enable
sustainable development in these agriculturally dominated catchments. |
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