The Water Balance and Stable Isotope Hydrology of Lake Edward Uganda-Congo.pdf

J. Great Lakes Res. 32:77–90 Internat. Assoc. Great Lakes Res., 2006 The Water Balance and Stable Isotope Hydrology of Lake Edward, Uganda-Congo James M. Russell1,* and Thomas C. Johnson2 1Department of Geological Sciences Brown University Box 1846 Providence, Rhode Island 02912 2Large Lakes Observatory University of Minnesota Duluth 10 University Drive, RLB Duluth, Minnesota 55812 ABSTRACT. Lake Edward, Uganda-Congo, is one of the least studied of the great lakes of East Africa, and little is known of its physical hydrology. Stable isotope data and modeling and previously published estimates of Lake Edward’s water balance are used to constrain the physical hydrology of the lake, and particularly the relative proportion of surface outflow to evaporative water losses. Stable isotope calcula- tions suggest that Lake Edward loses roughly 50% of its water income by evaporation, while reviews of published hydrologic data together with our calculations suggest that evaporation comprises 54% of water losses. The similarity of these two sets of calculations lends credence to their validity, and provides a new water budget for the lake. Our results have important implications for the chemistry and hydrocli- matic sensitivity of Lake Edward. INDEX WORDS: Lake Edward, East Africa, rift lake, stable isotope, hydrology. INTRODUCTION The Great Lakes of East Africa are rich sources of information about past variations of the African monsoons. The potential for these lakes to record past variations in monsoon intensity is partly due to their hydrologic sensitivity that is driven by hydro- logic budgets for the lakes in which water losses are dominated by evaporation (Spigel and Coulter 1996). Lake Edward, located on the equator at the border between Uganda and the Democratic Repub- lic of the Congo, has received perhaps the least at- tention of the East African Great Lakes, despite paleoclimatic studies that have revealed a rich and varied paleoclimatic history for the lake (e.g.,