Reprinted from JOURNAL OF HYDROLOGY Origin and function of a closed depression in equatorial humid zones: the Lake Télé in North Congo Scope of the journal

The Journal of Hydrology publishes original research papers and comprehensive reviews in all the subfields of the hydrological sciences. These comprise, but are not limited to the physical, chemical, biogeochemical, stochastic and systems aspects of surface and groundwater hydrology, hydrometeorology and hydrogeology. Relevant topics in related disciplines such as climatology, water resource systems, hydraulics, agrohydrology, geomorphology, soil science, instrumentation and remote sensing, civil and environmental engineering are also included. Papers have empirical, theoretical and applied orientations. Publication information Journal of . For 1998 volumes 200-21 3 are scheduled for publication. Subscription prices are available upon request from the publishers. Subscriptions are accepted on a prepaid basis only and are entered on a calendar year basis. Issues are sent by surface mail except to the following countries where air delivery via SAL (Surface Air Lifted) mail is ensured: Argentina, Australia, Brazil, Canada, Hong Kong, India, Israel, Japan", Malaysia, Mexico, New Zealand, Pakistan, China, Singapore, South Africa, South Korea, Taiwan, Thailand, USA. For all other countries airmail rates are available upon request. Claims for missing issues must be made within 6 months of our publication (mailing) date. DËrivatibe-Works Subscribers may reproduce tables of contents or prepare lists of articles including abstracts for internal circulation within their institutions. Permission of the publisher is required for resale or distribution outside the institution. Permission of the publisher is required for all other derivative works. including compilations and translations. Electronic Storage Permission of the publisher is required to store electronically any material contained in this journal. including any article or part of an article. Contact the pub!isher at the address indica!ed. Except as outlined above, no part of this publication may be reproduced, stored in a retrieval syslem or lransmitted in any form or by any means, eleclronlc. mechanlcal. photocopying. recording or otherwise, without prior written permission o f the publisher. Abstract Lake Télé has a nearly perfect ellipsoidal shape and is surrounded by swamps and barely penetrable flooded forests in the heart of the Congo-Zaïre watershed basin, and has intrigued the international scientific community for decades. In June 1992, a first Franco-Congolese multidisciplinary scientific expedition was finally able to reach the lake which is vast (23 km') and shallow (3 m). Its volume is estimated at 71 x IO6 m3 and is 40% filled with an organic silt layer a metre thick. Its hydrological exchanges are almost exclusively vertical with very little lateral contribution from the surrounding swamp. This leads to the observation that the waters are very slightly mineralized (< 3 mg I-'], but are very rich in organic carbon (44% of suspended matter and of total dissolved matter) and are very acidic (pH < 4). In addition, a magnetic anomaly of some hundred nanoTesla from a magnetic body at shallow depth has been detected in the lake's northern half, although its origin remains unknown. Botanical and palynological observations suggest the persistence of a strongly hydromorphic forest environment for at least the last 6600 years. Identified pollen taxa, whether ancient or recent, come mainly from pioneer and colonizing taxa such as Macaranga, which tends to indicate that the forest is continuing to gradually fill in the lake.