The modern sediments and human impacts in some Middle Atlas lakes (Morocco)(PICS Project)
by
B. Damnati
Faculté des Sciences et Techniques. Department of Earth Sciences. Natural Resources and Risks Observatory. B.P. 416. Tanger. Morocco
Coauthors: M. Taieb (CEREGE. BP 80. 13545. Aix-en-Provence Cedex 04 France), D. Arnaud (CNRS. Chemin Joseph Aiguier. 13009. Marseille. Cedex 09 France), M. Decobert (CEREGE. BP 80. 13545. Aix-en-Provence Cedex 04 France), A. Marais (CEREGE. BP 80. 13545. Aix-en-Provence Cedex 04 France)

The aim of lakes systems study in Morocco is : to track the human impact related to the deforestation and to the agricultural development; to compare these signals with current natural proxies ; to estimate the sedimentation rate regarding the rainfall variations and to determine theclimatic change during the Holocene.

A campaign of core sampling has been conducted November, 2000 in the Middle Atlas region. Some lakes were visited and sampled. The superficial sediments were sampled by a Kajack corer (1 m of long) and the Holocene deposits with a hand piston corer.

It concerns mostly small lakes accommodated in karstic washbasins. These sites receive the main precipitation from the Atlantic origin. The waters are alkaline and calco-magnesien (electric specific conductivity 600-840 mS / cm, pH average is about 8,8).

We present here some preliminary results of the modern sediments in three lakes: the lake Ifrah, the lake Aguelmane Ntifounassine and the lake Aguelmane Sidi Ali.

In Lake Aguelmane Ntifounassine the modern sediments are relatively rich in organic matter (between 10 and 25 %). There is a very interesting correlation between organic matter and magnetic susceptibility.

The Lake Aguelmane Sidi Ali is a relatively big (1.5 km in length and about 500 m wide); it is situated at about 2080 m of height near the Zad Col. It is not fed with rivers. Carbonate deposits were observed on the borders of the lake in connection with a period of low lake level stand related to dry climatic conditions. The water of this lake is alkaline. The human impact is notably present by the action of breeding and the tourism . The superficial sediments are more sandy. The contents in organic matter are weak and remain relatively constant (< 10 %).

In Lake Ifrah, samples of water and a core were taken. The existing of some houses around the lake, as well as the existence of pollen taxa associated with culture fields just few cm above a level with cedar tree seems related to human deforestation.

Date received: May 10, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahi-86.