Three forms of algal mats : subaerial, emersed and submersed, and their species composition, structure and stratification were studied for a period of twelve months (1996-1997) in an irrigation canal at Al-Kharj, Saudi Arabia. The development of the mats is a continuous process in a gradient fashion from the outlet of a piedmont cave-lake to the end of the canal. The growth maxima occurred at the first weir, which is subject to fast water-current and spray-wetted zone. Mats developed as discrete associations, recognizable by their colour and shape. Hard lithified, soft and floppy, and thin crust types of mats developed in their respective zones and comprised separate biotic communities. Ecological factors such as the nature of the microhabitat, water-chemistry, fluctuation in water-flow, depth of water column, splashing and temperature may have influenced their formation. The emersed mats with Phormidium tenue were predominant from November to February, whereas the subaerial mats above with Tolypothrix distorta adhere to the canal wall as a permanent feature. The subaerial mat has stromatolite-like morphology and is considered a nuisance to the water and drainage maintenance.

The river Nile is the main source of drinking water in Egypt. Nutrient loading coupled with year-round warm weather favor the growth of cyanobacteria, several of which can produce cyanotoxins, especially the potent liver toxins called microcystins. Most microcystin resides inside or closely attached to cyanobacteria cells, and are released into the water column as cells lyse from senescence or chemical treatment. The present study evaluated microcystin levels, as measured by immunoassay (ELISA), in both raw and finished drinking water of the river Nile, during the warm season (May-October), near the drinking water intake for Sohag City, Egypt. The results showed that microcystin content within the cells correlated better with type of microcystin-producing cyanobacteria (Gomphosphaeria, Microcystis, Oscillatoria) rather than chlorophyll a. Microcystin concentration in cell-free water correlated significantly with that measured within the cells, with maximum values being recorded in September (0.4-0.78 µg l-1). Microcystin levels in the finished drinking water were low (56.1- 87.1 ng l-1) and were detected only in May and June. The study indicates that microcystin is present in the raw and finished drinking water at Sohag City but that levels did not exceed the World Health Organization (WHO) drinking water guideline level of 1µg l-1 during May-October 1999.

A critical comparison of four techniques used to estimate the abundance and biomass of bacteria associated with leaves decaying in a small river in the North-East of Morocco is given. The relative efficiency of the four methods was as follows: homogenisation > direct count > stomacher > sonication. However, each one of these techniques presents its advantages and disadvantages. No technique is perfect by itself.

As part of a survey of the rotifer fauna of Burundi, Lecanidae from Kashira and the floodplain of the river Rusizi in Northwest Burundi are reported. Thirty-four species of Lecane were found. Twenty-five of them are new to Burundi, raising the total Burundian Lecane record to thirty-five. Three species, Lecane aeganea Harring, 1914, L. eswari Dhanapathi, 1976 and L. subulata (Harring & Myers, 1926) are new to the African fauna, the presence of L. baimaii Sanoamuang & Savatenalinton, 1999 in Africa is confirmed. The fauna consists mainly of cosmopolitan and tropicopolitan taxa, accompanied by several Eastern Hemisphere taxa, and one each of pantropical, endemic and arctic-temperate taxa. The latter, occurring in a high-altitude locality, may be a glacial relict.

L'étude de la faune madicole est fort peu avancée aux tropiques. En Guadeloupe, l'étude d'un vaste habitat madicole typique dans le massif de la Soufrière a été entreprise. La faune comporte un nombre d'éléments eumadicoles ou au moins madicophiles : Hydracariens, Diptères, et surtout Trichoptères. Parmi les 10 espèces de Trichoptères appartenant à ces catégories, plusieurs sont soit des nouveautés pour la faune de la Guadeloupe, soit représentées par des [math] pas encore décrites au niveau de l'espèce pour être nommées ; le cas le plus remarquable est celui de la stricte coexistence de deux espèces de Byrsopteryx, dont une décrite comme nouvelle, et qui se distinguent par la coloration des ailes et par la structure des tergites abdominaux, leurs genitalia [math] semblant être identiques. Les Trichoptères de 4 cours d'eau auparavant non échantillonnés et appartenant à des zones différentes ont été collectés à la lumière UV, ce qui permet certaines comparaisons. La description de deux espèces endémiques pour la Guadeloupe est complétée. 47 espèces de Trichoptères sont actuellement connues de Guadeloupe.

The origin of the water of the two Sidi Harazem springs (Morocco), was found to be different. Environmental parameters made it possible to recognise three types of water : one issuing from a "cool spring", with lowest temperature (mean : 26.7°C), conductivity and chloride concentration ; one issuing from the "hot spring" (mean : 31.7°C) with the highest temperature and high conductivity ; and the one of the oued itself with into which both springs flow. This oued had the highest values of pH, conductivity, chlorides, and calcium. The interstitial fauna collected by means of artificial substrates was composed of both epigean and stygobite species. Only the "cool spring" included stygobite species, the number of which generally decreased with depth.