Space and time variations in the isotopic composition (delta H-2-delta O-18) of Niger inland delta water (Mali).

The Niger inland delta is a flooded zone of major economic importance, Evap oration is higher than precipitation and the flooded surfaces depend on Nig er and Bani Rivers' inflow. Rainwater data pointed to an isotopic variabili ty due to various climatic conditions and rainfall origins. In the upper ba sin, values are influenced by groundwater, sub-surface storage and direct r unoff in turn affected by high evaporation rates during the low water stage . Because of low hydraulic gradient, the isotopic variations are dominated by evaporation. Nevertheless, the spatial evolution is not as important as expected. A vapour re-equilibration with the river surface can reduce isoto pe fractionation. (C) 2000 Academie des sciences / Editions scientifiques e t medicales Elsevier SAS.