European Diatom Database-North African Dataset

The European Diatom Database (EDDI) is a web-based information system designed
to enhance the application of diatom analysis to problems of surface water
acidification, eutrophication and climate change.

The North African dataset consists from samples from Tunisia (66), Algeria (3),
Morocco (26), and Niger (20). In Tunisia, samples were collected from the
Mediterranean northern regions to the margins of the Sahara southwards by L.
Ben Khelifa and F. Gasse (1985-1989). In southern Tunisia, samples were taken
from small permanent groundwater-fed waterbodies and temporary salt lakes,
small artificial ponds developed around boreholes, and in mini reservoir lakes
and swamps along Wadi el Akarit. Samples from hydrothermal springs have been
collected throughout the country. In northern Tunisia, freshwater samples were
also taken from the Mejerda Channel. Waters range from fresh to metasaline.
Most samples are of the sodium/chloride or calcium-magnesium/ sulphate type.
Diatoms were counted by L. Ben Khelifa. Details of diatom and hydrochemical
analyses are given in Ben Khelifa (1989). Sites from southern Algeria,
collected by F. Gasse en 1985, show clear similarities with the waterbodies of
southern Tunisia. The 26 samples from Morroco were collected by F. Gasse in
1989 from 17 localities situated between 30?30-34?30N and 5?-7?30E, at altitude
ranging from 300 to 2050 m. Sites are distributued in the western plains close
to Casablanca, the Middle Atlas mountains, and the more arid southweast margins
of the Atlas ranges, from a large variety of waterbodies (permanent and
temporary natural lakes, man-made lakes, and wadis. Conductivities range from
195 to 3900 ?S cm-1. Freshwaters are of the calcium-sodium/bicarbonate type,
while oligosaline waters are of the sodium/chloride type. Diatom samples were
counted by F. Gasse. In southern Niger, samples were collected from the Niger
River, the Bara salt pond near Niamey, and from interdunal depressions on the
Manga Plateau occupied by permanent or ephemeral waterbodies. A few samples
from northern Niger (A?r) have also been collected from groundwater-supplied
ponds. Most waterbodies are of the sodium/carbonate-bicarbonate type. Samples
from Niger were collected and analyzed by F. Gasse, except those from the Bara
pond (M.-C. Lang). The main characteristics of the water chemistry and diatom
communities of the Niger samples are presented in Gasse (1987).