Adel A. Fathi

Radiometrically determined dates and sedimentation rates for recent sediments in nine North African wetland lakes (the CASSARINA Project)

Sediment cores were collected from nine wetland lakes in Morocco, Tunisia and Egypt for the CASSARINA project investigating environmental change in Northern African wetlands. The cores were dated radiometrically by using natural (210Pb) and artificial (137Cs and 241Am) radionuclides. At sites in Morocco and Tunisia with mean annual rainfall totals ranging from 500–1000 mm yr−1, fallout records were generally satisfactory and it was possible to develop independent sediment chronologies based on the radiometric data alone. At the Egyptian sites, rainfall was less than 200 mm yr−1 and fallout records were much less distinct. At these sites the radiometric data could only be used to give an indication of mean sedimentation rates during the past 30–40 years. By using a combination of fallout radionuclide, pollen, and macrofossil stratigraphic records it was however possible to determine a credible sediment chronology spanning the major part of the 20th century. Applying this chronology to records of spheroidal carbonaceous particles (SCP) from the same sediment cores, the onset of significant levels of atmospheric pollution in the Nile Delta is dated in all three cores to the mid 1950s. Results from a number of lakes (Sidi Bou Rhaba, Ichkeul and Korba) revealed high and accelerating siltation rates, threatening their continued existence beyond the next few decades. In contrast, sedimentation rates at all three Nile Delta sites appear to have declined in recent decades, most probably due to the impact of the Nile barrages.

Water quality and phytoplankton communities in Lake Qarun (Egypt)

Abstract.Lake Qarun is a closed saline lake in the northern part of El-Fayoum Depression (Middle Egypt) at the margin of the Great Western Desert. It is almost entirely sustained by inflow from the Nile River and, during the 20th century, lake water salinity has increased strongly. Physico-chemical characteristics and phytoplankton periodicity in the lake were monitored during 2001. All the water quality variables measured showed considerable seasonal variation, and quantitative and qualitative differences in phytoplankton communities were recorded. The maximum crop density was in August, whereas lowest values occurred in December. Highest crop densities coincided with a high abundance of Bacillariophyceae. The Bacillariophyceae were most diverse with 23 species, then Chlorophyceae with 16, Cyanophyceae with 8, and Chrysphyceae and Dinophyceae with one species each. Despite being a saline inland lake, the open-water phytoplankton communities were composed of some marine/brackish forms but mainly of freshwater communities tolerant to high salinity. The identified phytoplankton species indicate a tendency towards eutrophy but total crop densities were relatively low compared with eutrophic lakes elsewhere. Light limitation by suspended solids as well as hydrological related factors are believed responsible for the relatively low phytoplankton abundance. The lake appears to be ecologically unstable and careful limnological monitoring is recommended.

Palaeolimnological responses of nine North African lakes in the CASSARINA Project to recent environmental changes and human impact detected by plant macrofossil, pollen, and faunal analyses

This paper presents multi-proxy palaeolimnological analyses from recent sediments in the nine CASSARINA lakes in northernmost Africa, three from each of Morocco, Tunisia, and Egypt. The lakes are diverse, ranging from hypersaline to brackish lagoons and fresh-water lakes from high to low conductivity and pH. The macrofossils analysed include fruits, seeds, and vegetative remains of plants, lagoon and fresh-water Mollusca, a range of other aquatic animals, and from one site in each country, Ostracoda and Foraminifera. The diverse macrofossils are multi-proxy indicators of environmental change, and demonstrate changes in response to human activities in the catchments of all the lakes. The three Egyptian Nile Delta lakes have received massive inputs of fresh-water due to modifications of the flow of the R. Nile culminating in the Aswan High Dam built in 1964. Elsewhere, water withdrawal is frequently a serious threat. One lake with high biodiversity in Morocco has been drained and cultivated, and a rare acid-water lake in Tunisia is in danger of drying up. The internationally famous Garaet El Ichkeul in Tunisia, which was so important for birds, has become permanently saline with a loss of diversity. All the lakes are affected by agricultural and/or urban run-off and are experiencing changes as a result of human activities. Several are in a marginally sustainable condition, whereas others are permanently damaged.

Phytoplankton communities of North African wetland lakes: the CASSARINA Project

Seasonal variations in phytoplankton species composition (frequencies) and densities (cell numbers) in nine North African coastal lakes selected in Morocco (Merja Sidi Bou Rhaba, Zerga and Bokka), Tunisia (Chitane, Ichkeul and Korba lakes) and Egypt (Edku, Burullus and Manzala lakes) were investigated during 1998. The main aim was to provide gase-line information about overall phytoplankton diversity and how phytoplanktoncharacteristics differ between these contrasting aquatic systems.Water samples were collected at approximately three monthly intervals and phytoplankton analysis revealed marked seasonal and spatial differences in the quantitative and qualitative composition of the communities at each site. The Egyptian lakes generally had larger crops (Manzala and Burullus had mean crop densities of more than 104 cells ml−1) but in the western North African sites only Korba and Sidi Bou Rhaba had closely comparable densities. Algae belonging to Bacillariophyceae, Chlorophyceae, Chrysophyceae, Cyanophyceae, Dinophyceae and Euglenophyceae were recorded. Taxa representative of all these algal groups occurred in two lakes (Korba and Manzala) but at the other seven sites only some of the groups were present.The Chlorophyceae was the most dominant group in lakes Burullus, Manzala, Korba and Sidi Bou Rhaba whereas Bacillariophyceae were dominant in lakes Zerga, Bokka and Edku. In Ichkeul and acidic Chitane the Dinophyceae and the Cyanophyceae were the dominant groups, respectively. The maximum percentage of Euglenophyceae occurred in Edku Lake but this group was absent in Sidi Bou Rhaba and Ichkeul. Cyanophyceans were present in significant numbers in all investigated lakes except in Ichkeul. A total of fifty-three genera were recorded, 17 of Chlorophyceae, 18 of Bacillariophyceae, 11 of Cyanophyceae, 3 of Chrysophyceae, 2 of Euglenophyceae and 2 of Dinophyceae. The maximum number of species (34) occurred in Burullus Lake and the minimum (6) in Ichkeul Lake. Only one lake (acidic Chitane) possessed species indicative of oligotrophic conditions. The Nile Delta lakes were the most species diverse sites.The phytoplankton communities of the nine North African lakes were composed entirely of cosmopolitan species but with one new species (Cyclotella choctawatcheeana) was recorded for the region. The data presented provide a contemporary account of the levels of algal diversity present in these sites at the end of the 20th century. The relevance of phytoplankton communities to assessment of lake status and future monitoring studies in the region is emphasised.

Recent environmental change in North African wetland lakes: diatom and other stratigraphic evidence from nine sites in the CASSARINA Project

All nine wetland lakes in the CASSARINA North African suite of sample sites have been disturbed strongly by human activity during the 20th century. Dated lake sediment core were used to provide evidence of the extent of recent environmental change at each site. Sedimentary diatoms at seven sites were useful for inferring salinity change trends during the last century. At two sites preservation problems severely degraded the sedimentary diatom record. Sediment core integrity was otherwise established.Lithostratigraphic measurements indicated some site specific changes in soil erosion and sediment composition but, for the Egyptian Delta lakes, no physical signal synchronous with Aswan High Dam construction was found. Sedimentary diatom assemblages were generally site characteristic and halophilous taxa were common. At two sites planktonic diatoms indicated some recent eutrophication but generally the assemblages were more indicative of salinity changes. Diatom-inferred salinity trends for the seven sites typically indicated that reductions in water salinity occurred sometime during the early or mid 20th century.Rather than climate, hydrological modification of water resources is implicated as the primary driver of salinity changes during most of the 20th century. In the western North African region these modifications were mainly local land drainage and water diversion programmes to alleviate winter flooding and/or promote summer water availability. In the Delta region, the Nile has been intensively exploited since antiquity and intensively so from the late 19th century to release more fresh water for agriculture. Here, diatom records indicate that freshening began well before the Aswan High Dam but salinity fluctuations have tended to diminish during the latter part of the 20th century. A small reversal in the water freshening trend in the 1980/90s was possibly a response to land subsidence/sea-level change or to reduced freshwater supply.Freshwater supply to the sites is generally diminishing as former freshwater surpluses switch to deficit. One site (Merja Bokka, Morocco) became completely dry in 1998 as agriculture encroached and Megene Chitane, the only acid lake in Tunisia, is currently affected by excessive inflow abstraction. At the beginning of the 21st century, eight of the nine CASSARINA sites persist as viable but modified aquatic ecosystems. They nevertheless continue to support valuable aquatic biodiversity, especially in the Delta sites and in Chitane. The modern diatom communities are clearly tolerant of considerable environmental change but the remaining sites are increasingly threatened by major hydrological disturbance. Base-line floristic data for the late 20th century are given but continuous biomonitoring combined with effective management is needed urgently to help conserve North Africas diminishing natural wetland lake resources.

Terrestrial pollen record of recent land-use changes around nine North African lakes in the CASSARINA Project

Pollen analyses and related plant macrofossil records are presented from short cores from nine North African lakes in the EU-funded CASSARINA project. Terrestrial pollen reflects human impact on the vegetation and landscape over the last 150–100 years. Pollen changes, aided by radiometric dating, could be correlated with historical developments. The chronology of the landscape changes date other biostratigraphical records reflecting changes in the aquatic ecosystems.Three lakes in Morocco show gradually intensifying land-use over the last century. Accelerated technological development and landscape modification over the last 20 years culminated in one of the lakes being drained and cultivated during the project period. In Tunisia, a nationally unique acid-water lake is threatened by water withdrawal for increased catchment cultivation. The landscape around two other lakes is being increasingly cultivated and urbanised, and water withdrawal to support this has resulted in deleterious effects on the aquatic ecosystems, particularly at the internationally famous Garaet El Ichkeul where reed-marshes and macrophyte beds have been lost. The three lakes in the Egyptian Nile Delta are in the same hydrological system and show parallel changes in the balance between saltmarsh and reed-marsh. Control of Nile floods and year-round irrigation led to marked increases in cultivation in the delta region since ca. 1920. The Aswan High Dam (1964) had little detectable further effect. Documented planting of dates, palms, and olives and of introduced Casuarina and Eucalyptus trees provided a chronology to supplement the unsatisfactory radiometric dating of the sediments in this low-rainfall area.

Recent environmental change in North African wetland lakes: a baseline study of organochlorine contaminant residues in sediments from nine sites in the CASSARINA project.

Sediment from 9 lakes and lagoons in 3 North African countries was analysed for a suite of organochlorine insecticides and polychlorinated biphenyls (PCBs). Residues of γ-HCH and pp′-DDE were detected in most cores, and radiometric dating of the sediment enabled time profiles to be constructed which are indicative of recent use of the insecticide lindane and previous use of the insecticide DDT in the region. Absolute concentrations of these pesticides were relatively low compared to reported values for other world-wide locations, but exceeded recommended Canadian and Dutch environmental quality standards at several sites. Maximum fluxes of γ-HCH and pp′-DDE (190 and 95 μg m−2 yr−1, respectively) were relatively high and comparable to some sediments in North America and the United Kingdom. Other organochlorine pesticides including dieldrin were detected at low levels in some samples. Selected PCB congeners were detected at trace levels at 2 sites only, indicating low levels of industrial contamination at the sampling locations. Tropical and sub-tropical regions of the world have been suggested to be contemporary sources of globally distributed organochlorine contaminants. These data are discussed with respect to this hypothesis.

Some observations on the age and growth of thin-lipped grey mullet, Liza ramada Risso, 1826 (Pisces, Mugilidae) in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt)

Age and growth characteristics of the thin-lipped Grey Mullet (Liza ramada) were investigated in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt). Age structure of the mullet populations was very similar in all three study lakes. Small differences in growth were indicated, especially for the Moroccan population, where growth tended to be slower than for the other two populations. The fastest growth was observed in the Edku population while the best condition was observed in the Ichkeul population. Compared with some European populations, the sampled North African populations have faster growth and better condition factors.